2. You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.
3. How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.
4. Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.
5. Give two examples of how you might determine the structure of the table DEPT.
Use the describe command or use the dbms_metadata.get_ddl package.
6. Where would you look for errors from the database engine?
In the alert log.
7. Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.
8. Give the reasoning behind using an index.
Faster access to data blocks in a table.
9. Give the two types of tables involved in producing a star schema and the type of data they hold.
Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.
10. What type of index should you use on a fact table?
A Bitmap index.
11. Give two examples of referential integrity constraints.
A primary key and a foreign key.
12. A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables?
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.
13. Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any ball in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any ball in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.
14. What command would you use to create a backup control file?
Alter database backup control file to trace.
15. Give the stages of instance startup to a usable state where normal users may access it.
STARTUP NOMOUNT - Instance startup
STARTUP MOUNT - The database is mounted
STARTUP OPEN - The database is opened
16. What column differentiates the V$ views to the GV$ views and how?
The INST_ID column which indicates the instance in a RAC environment the information came from.
17. How would you go about generating an EXPLAIN plan?
Create a plan table with utlxplan.sql.
Use the explain plan set statement_id = 'tst1' into plan_table for a SQL statement
Look at the explain plan with utlxplp.sql or utlxpls.sql
18. How would you go about increasing the buffer cache hit ratio?
Use the buffer cache advisory over a given workload and then query the v$db_cache_advice table. If a change was necessary then I would use the alter system set db_cache_size command.
19. Explain an ORA-01555
You get this error when you get a snapshot too old within rollback. It can usually be solved by increasing the undo retention or increasing the size of rollbacks. You should also look at the logic involved in the application getting the error message.
20. Explain the difference between $ORACLE_HOME and $ORACLE_BASE.
ORACLE_BASE is the root directory for oracle. ORACLE_HOME located beneath ORACLE_BASE is where the oracle products reside.
1. Describe the difference between a procedure, function and anonymous pl/sql block.
Candidate should mention use of DECLARE statement, a function must return a value while a procedure doesn?t have to.
2. What is a mutating table error and how can you get around it?
This happens with triggers. It occurs because the trigger is trying to update a row it is currently using. The usual fix involves either use of views or temporary tables so the database is selecting from one while updating the other.
3. Describe the use of %ROWTYPE and %TYPE in PL/SQL
Expected answer: %ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type.
4. 4What packages (if any) has Oracle provided for use by developers?
Expected answer: Oracle provides the DBMS_ series of packages. There are many which developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and describe how they used them, even better. If they include the SQL routines provided by Oracle, great, but not really what was asked.
5. Describe the use of PL/SQL tables
Expected answer: PL/SQL tables are scalar arrays that can be referenced by a binary integer. They can be used to hold values for use in later queries or calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.
6. When is a declare statement needed ?
The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if it is used.
7. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?
Expected answer: OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL.
8. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
Expected answer: SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.
9. How can you find within a PL/SQL block, if a cursor is open?
Expected answer: Use the %ISOPEN cursor status variable.
10. How can you generate debugging output from PL/SQL?
Expected answer: Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE can also be used.
11. What are the types of triggers?
Expected Answer: There are 12 types of triggers in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL key words:
BEFORE ALL ROW INSERT
AFTER ALL ROW INSERT
BEFORE INSERT
AFTER INSERT etc.
1. Give one method for transferring a table from one schema to another:
There are several possible methods, export-import, CREATE TABLE... AS SELECT, or COPY.
2. What is the purpose of the IMPORT option IGNORE? What is it?s default setting
The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is not specified the tables that already exist will be skipped. If it is specified, the error is ignored and the tables data will be inserted. The default value is N.
3. You have a rollback segment in a version 7.2 database that has expanded beyond optimal, how can it be restored to optimal
Use the ALTER TABLESPACE ..... SHRINK command.
4. If the DEFAULT and TEMPORARY tablespace clauses are left out of a CREATE USER command what happens? Is this bad or good? Why
The user is assigned the SYSTEM tablespace as a default and temporary tablespace. This is bad because it causes user objects and temporary segments to be placed into the SYSTEM tablespace resulting in fragmentation and improper table placement (only data dictionary objects and the system rollback segment should be in SYSTEM).
5. What are some of the Oracle provided packages that DBAs should be aware of
Oracle provides a number of packages in the form of the DBMS_ packages owned by the SYS user. The packages used by DBAs may include: DBMS_SHARED_POOL, DBMS_UTILITY, DBMS_SQL, DBMS_DDL, DBMS_SESSION, DBMS_OUTPUT and DBMS_SNAPSHOT. They may also try to answer with the UTL*.SQL or CAT*.SQL series of SQL procedures. These can be viewed as extra credit but aren?t part of the answer.
6. What happens if the constraint name is left out of a constraint clause
The Oracle system will use the default name of SYS_Cxxxx where xxxx is a system generated number. This is bad since it makes tracking which table the constraint belongs to or what the constraint does harder.
7. What happens if a tablespace clause is left off of a primary key constraint clause
This results in the index that is automatically generated being placed in then users default tablespace. Since this will usually be the same tablespace as the table is being created in, this can cause serious performance problems.
8. What is the proper method for disabling and re-enabling a primary key constraint
You use the ALTER TABLE command for both. However, for the enable clause you must specify the USING INDEX and TABLESPACE clause for primary keys.
9. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause
The index is created in the user?s default tablespace and all sizing information is lost. Oracle doesn?t store this information as a part of the constraint definition, but only as part of the index definition, when the constraint was disabled the index was dropped and the information is gone.
10. (On UNIX) When should more than one DB writer process be used? How many should be used
If the UNIX system being used is capable of asynchronous IO then only one is required, if the system is not capable of asynchronous IO then up to twice the number of disks used by Oracle number of DB writers should be specified by use of the db_writers initialization parameter.
11. You are using hot backup without being in archivelog mode, can you recover in the event of a failure? Why or why not
You can?t use hot backup without being in archivelog mode. So no, you couldn?t recover.
12. What causes the "snapshot too old" error? How can this be prevented or mitigated
This is caused by large or long running transactions that have either wrapped onto their own rollback space or have had another transaction write on part of their rollback space. This can be prevented or mitigated by breaking the transaction into a set of smaller transactions or increasing the size of the rollback segments and their extents.
13. How can you tell if a database object is invalid
By checking the status column of the DBA_, ALL_ or USER_OBJECTS views, depending upon whether you own or only have permission on the view or are using a DBA account.
13. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check
You need to check that the user has specified the full name of the object (select empid from scott.emp; instead of select empid from emp;) or has a synonym that balls to the object (create synonym emp for scott.emp;)
14. A developer is trying to create a view and the database won?t let him. He has the "DEVELOPER" role which has the "CREATE VIEW" system privilege and SELECT grants on the tables he is using, what is the problem
You need to verify the developer has direct grants on all tables used in the view. You can?t create a stored object with grants given through views.
15. If you have an example table, what is the best way to get sizing data for the production table implementation
The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows.
16. How can you find out how many users are currently logged into the database? How can you find their operating system id
There are several ways. One is to look at the v$session or v$process views. Another way is to check the current_logins parameter in the v$sysstat view. Another if you are on UNIX is to do a "ps -efgrep oraclewc -l? command, but this only works against a single instance installation.
17. A user selects from a sequence and gets back two values, his select is:
SELECT pk_seq.nextval FROM dual;What is the problem
Somehow two values have been inserted into the dual table. This table is a single row, single column table that should only have one value in it.
18. How can you determine if an index needs to be dropped and rebuilt
Run the ANALYZE INDEX command on the index to validate its structure and then calculate the ratio of LF_BLK_LEN/LF_BLK_LEN+BR_BLK_LEN and if it isn?t near 1.0 (i.e. greater than 0.7 or so) then the index should be rebuilt. Or if the ratio
BR_BLK_LEN/ LF_BLK_LEN+BR_BLK_LEN is nearing 0.3
1. How can variables be passed to a SQL routine
By use of the & symbol. For passing in variables the numbers 1-8 can be used (&1, &2,...,&8) to pass the values after the command into the SQLPLUS session. To be prompted for a specific variable, place the ampersanded variable in the code itself:
"select * from dba_tables where owner=&owner_name;" . Use of double ampersands tells SQLPLUS to resubstitute the value for each subsequent use of the variable, a single ampersand will cause a reprompt for the value unless an ACCEPT statement is used to get the value from the user.
2. You want to include a carriage return/linefeed in your output from a SQL script, how can you do this
The best method is to use the CHR() function (CHR(10) is a return/linefeed) and the concatenation function "". Another method, although it is hard to document and isn?t always portable is to use the return/linefeed as a part of a quoted string.
3. How can you call a PL/SQL procedure from SQL
By use of the EXECUTE (short form EXEC) command.
4. How do you execute a host operating system command from within SQL
By use of the exclamation ball "!" (in UNIX and some other OS) or the HOST (HO) command.
5. You want to use SQL to build SQL, what is this called and give an example
This is called dynamic SQL. An example would be:
set lines 90 pages 0 termout off feedback off verify off
spool drop_all.sql
select ?drop user ?username? cascade;? from dba_users
where username not in ("SYS?,?SYSTEM?);
spool off
Essentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ?? the values selected from the database.
6. What SQLPlus command is used to format output from a select
This is best done with the COLUMN command.
7. You want to group the following set of select returns, what can you group on
Max(sum_of_cost), min(sum_of_cost), count(item_no), item_no
The only column that can be grouped on is the "item_no" column, the rest have aggregate functions associated with them.
8. What special Oracle feature allows you to specify how the cost based system treats a SQL statement
The COST based system allows the use of HINTs to control the optimizer path selection. If they can give some example hints such as FIRST ROWS, ALL ROWS, USING INDEX, STAR, even better.
9. You want to determine the location of identical rows in a table before attempting to place a unique index on the table, how can this be done
Oracle tables always have one guaranteed unique column, the rowid column. If you use a min/max function against your rowid and then select against the proposed primary key you can squeeze out the rowids of the duplicate rows pretty quick. For example:
select rowid from emp e
where e.rowid > (select min(x.rowid)
from emp x
where x.emp_no = e.emp_no);
In the situation where multiple columns make up the proposed key, they must all be used in the where clause.
10. What is a Cartesian product
A Cartesian product is the result of an unrestricted join of two or more tables. The result set of a three table Cartesian product will have x * y * z number of rows where x, y, z correspond to the number of rows in each table involved in the join.
11. You are joining a local and a remote table, the network manager complains about the traffic involved, how can you reduce the network traffic
Push the processing of the remote data to the remote instance by using a view to pre-select the information for the join. This will result in only the data required for the join being sent across.
11. What is the default ordering of an ORDER BY clause in a SELECT statement
Ascending
12. What is tkprof and how is it used
The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.
13. What is explain plan and how is it used
The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must have an explain_table generated in the user you are running the explain plan for. This is created using the utlxplan.sql script. Once the explain plan table exists you run the explain plan command giving as its argument the SQL statement to be explained. The explain_plan table is then queried to see the execution plan of the statement. Explain plans can also be run using tkprof.
14. How do you set the number of lines on a page of output? The width
The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.
15. How do you prevent output from coming to the screen
The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.
16. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution
The SET options FEEDBACK and VERIFY can be set to OFF.
17. How do you generate file output from SQL
By use of the SPOOL command
1. A tablespace has a table with 30 extents in it. Is this bad? Why or why not.
Multiple extents in and of themselves aren?t bad. However if you also have chained rows this can hurt performance.
2. How do you set up tablespaces during an Oracle installation?
You should always attempt to use the Oracle Flexible Architecture standard or another partitioning scheme to ensure proper separation of SYSTEM, ROLLBACK, REDO LOG, DATA, TEMPORARY and INDEX segments.
3. You see multiple fragments in the SYSTEM tablespace, what should you check first?
Ensure that users don?t have the SYSTEM tablespace as their TEMPORARY or DEFAULT tablespace assignment by checking the DBA_USERS view.
4. What are some indications that you need to increase the SHARED_POOL_SIZE parameter?
Poor data dictionary or library cache hit ratios, getting error ORA-04031. Another indication is steadily decreasing performance with all other tuning parameters the same.
5. What is the general guideline for sizing db_block_size and db_multi_block_read for an application that does many full table scans?
Oracle almost always reads in 64k chunks. The two should have a product equal to 64 or a multiple of 64.
6. What is the fastest query method for a table
Fetch by rowid
7. Explain the use of TKPROF? What initialization parameter should be turned on to get full TKPROF output?
The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.
8. When looking at v$sysstat you see that sorts (disk) is high. Is this bad or good? If bad -How do you correct it?
If you get excessive disk sorts this is bad. This indicates you need to tune the sort area parameters in the initialization files. The major sort are parameter is the SORT_AREA_SIZe parameter.
9. When should you increase copy latches? What parameters control copy latches
When you get excessive contention for the copy latches as shown by the "redo copy" latch hit ratio. You can increase copy latches via the initialization parameter LOG_SIMULTANEOUS_COPIES to twice the number of CPUs on your system.
10. Where can you get a list of all initialization parameters for your instance? How about an indication if they are default settings or have been changed
You can look in the init.ora file for an indication of manually set parameters. For all parameters, their value and whether or not the current value is the default value, look in the v$parameter view.
11. Describe hit ratio as it pertains to the database buffers. What is the difference between instantaneous and cumulative hit ratio and which should be used for tuning
The hit ratio is a measure of how many times the database was able to read a value from the buffers verses how many times it had to re-read a data value from the disks. A value greater than 80-90% is good, less could indicate problems. If you simply take the ratio of existing parameters this will be a cumulative value since the database started. If you do a comparison between pairs of readings based on some arbitrary time span, this is the instantaneous ratio for that time span. Generally speaking an instantaneous reading gives more valuable data since it will tell you what your instance is doing for the time it was generated over.
12. Discuss row chaining, how does it happen? How can you reduce it? How do you correct it
Row chaining occurs when a VARCHAR2 value is updated and the length of the new value is longer than the old value and won?t fit in the remaining block space. This results in the row chaining to another block. It can be reduced by setting the storage parameters on the table to appropriate values. It can be corrected by export and import of the effected table.
13. When looking at the estat events report you see that you are getting busy buffer waits. Is this bad? How can you find what is causing it
Buffer busy waits could indicate contention in redo, rollback or data blocks. You need to check the v$waitstat view to see what areas are causing the problem. The value of the "count" column tells where the problem is, the "class" column tells you with what. UNDO is rollback segments, DATA is data base buffers.
14. If you see contention for library caches how can you fix it
Increase the size of the shared pool.
15. If you see statistics that deal with "undo" what are they really talking about
Rollback segments and associated structures.
16. If a tablespace has a default pctincrease of zero what will this cause (in relationship to the smon process)
The SMON process won?t automatically coalesce its free space fragments.
17. If a tablespace shows excessive fragmentation what are some methods to defragment the tablespace? (7.1,7.2 and 7.3 only)
In Oracle 7.0 to 7.2 The use of the 'alter session set events 'immediate trace name coalesce level ts#';? command is the easiest way to defragment contiguous free space fragmentation. The ts# parameter corresponds to the ts# value found in the ts$ SYS table. In version 7.3 the ?alter tablespace coalesce;? is best. If the free space isn?t contiguous then export, drop and import of the tablespace contents may be the only way to reclaim non-contiguous free space.
18. How can you tell if a tablespace has excessive fragmentation
If a select against the dba_free_space table shows that the count of a tablespaces extents is greater than the count of its data files, then it is fragmented.
19. You see the following on a status report:
redo log space requests 23
redo log space wait time 0
Is this something to worry about? What if redo log space wait time is high? How can you fix this
Since the wait time is zero, no. If the wait time was high it might indicate a need for more or larger redo logs.
20. What can cause a high value for recursive calls? How can this be fixed
A high value for recursive calls is cause by improper cursor usage, excessive dynamic space management actions, and or excessive statement re-parses. You need to determine the cause and correct it By either relinking applications to hold cursors, use proper space management techniques (proper storage and sizing) or ensure repeat queries are placed in packages for proper reuse.
21. If you see a pin hit ratio of less than 0.8 in the estat library cache report is this a problem? If so, how do you fix it
This indicate that the shared pool may be too small. Increase the shared pool size.
22. If you see the value for reloads is high in the estat library cache report is this a matter for concern
Yes, you should strive for zero reloads if possible. If you see excessive reloads then increase the size of the shared pool.
23. You look at the dba_rollback_segs view and see that there is a large number of shrinks and they are of relatively small size, is this a problem? How can it be fixed if it is a problem
A large number of small shrinks indicates a need to increase the size of the rollback segment extents. Ideally you should have no shrinks or a small number of large shrinks. To fix this just increase the size of the extents and adjust optimal accordingly.
24. You look at the dba_rollback_segs view and see that you have a large number of wraps is this a problem
A large number of wraps indicates that your extent size for your rollback segments are probably too small. Increase the size of your extents to reduce the number of wraps. You can look at the average transaction size in the same view to get the information on transaction size.
25. In a system with an average of 40 concurrent users you get the following from a query on rollback extents:
ROLLBACK CUR EXTENTS
--------------------- --------------------------
R01 11
R02 8
R03 12
R04 9
SYSTEM 4
26. You have room for each to grow by 20 more extents each. Is there a problem? Should you take any action
No there is not a problem. You have 40 extents showing and an average of 40 concurrent users. Since there is plenty of room to grow no action is needed.
27. You see multiple extents in the temporary tablespace. Is this a problem
As long as they are all the same size this isn?t a problem. In fact, it can even improve performance since Oracle won?t have to create a new extent when a user needs one.
28. Define OFA.
OFA stands for Optimal Flexible Architecture. It is a method of placing directories and files in an Oracle system so that you get the maximum flexibility for future tuning and file placement.
29. How do you set up your tablespace on installation
The answer here should show an understanding of separation of redo and rollback, data and indexes and isolation os SYSTEM tables from other tables. An example would be to specify that at least 7 disks should be used for an Oracle installation so that you can place SYSTEM tablespace on one, redo logs on two (mirrored redo logs) the TEMPORARY tablespace on another, ROLLBACK tablespace on another and still have two for DATA and INDEXES. They should indicate how they will handle archive logs and exports as well. As long as they have a logical plan for combining or further separation more or less disks can be specified.
30. What should be done prior to installing Oracle (for the OS and the disks)
adjust kernel parameters or OS tuning parameters in accordance with installation guide. Be sure enough contiguous disk space is available.
31. You have installed Oracle and you are now setting up the actual instance. You have been waiting an hour for the initialization script to finish, what should you check first to determine if there is a problem
Check to make sure that the archiver isn?t stuck. If archive logging is turned on during install a large number of logs will be created. This can fill up your archive log destination causing Oracle to stop to wait for more space.
32. When configuring SQLNET on the server what files must be set up
INITIALIZATION file, TNSNAMES.ORA file, SQLNET.ORA file
33. When configuring SQLNET on the client what files need to be set up
SQLNET.ORA, TNSNAMES.ORA
34. What must be installed with ODBC on the client in order for it to work with Oracle
SQLNET and PROTOCOL (for example: TCPIP adapter) layers of the transport programs.
35. You have just started a new instance with a large SGA on a busy existing server. Performance is terrible, what should you check for
The first thing to check with a large SGA is that it isn?t being swapped out.
36. What OS user should be used for the first part of an Oracle installation (on UNIX)
You must use root first.
37. When should the default values for Oracle initialization parameters be used as is
Never
38. How many control files should you have? Where should they be located
At least 2 on separate disk spindles. Be sure they say on separate disks, not just file systems.
39. How many redo logs should you have and how should they be configured for maximum recoverability
You should have at least three groups of two redo logs with the two logs each on a separate disk spindle (mirrored by Oracle). The redo logs should not be on raw devices on UNIX if it can be avoided.
40. You have a simple application with no "hot" tables (i.e. uniform IO and access requirements). How many disks should you have assuming standard layout for SYSTEM, USER, TEMP and ROLLBACK tablespaces
At least 7, see disk configuration answer above.
41. Describe third normal form
Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key
42. Is the following statement true or false:
"All relational databases must be in third normal form"
False. While 3NF is good for logical design most databases, if they have more than just a few tables, will not perform well using full 3NF. Usually some entities will be denormalized in the logical to physical transfer process.
43. What is an ERD
An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model.
44. Why are recursive relationships bad? How do you resolve them
A recursive relationship (one where a table relates to itself) is bad when it is a hard relationship (i.e. neither side is a "may" both are "must") as this can result in it not being possible to put in a top or perhaps a bottom of the table (for example in the EMPLOYEE table you couldn?t put in the PRESIDENT of the company because he has no boss, or the junior janitor because he has no subordinates). These type of relationships are usually resolved by adding a small intersection entity.
45. What does a hard one-to-one relationship mean (one where the relationship on both ends is "must")
Expected answer: This means the two entities should probably be made into one entity.
46. How should a many-to-many relationship be handled
By adding an intersection entity table
47. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used
A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key.
48. When should you consider denormalization
Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity.
49. How can you determine if an Oracle instance is up from the operating system level
There are several base Oracle processes that will be running on multi-user operating systems, these will be smon, pmon, dbwr and lgwr. Any answer that has them using their operating system process showing feature to check for these is acceptable. For example, on UNIX a ps -efgrep dbwr will show what instances are up.
50. Users from the PC clients are getting messages indicating :
ORA-06114: (Cnct err, can't get err txt. See Servr Msgs & Codes Manual)
What could the problem be
The instance name is probably incorrect in their connection string.
51. Users from the PC clients are getting the following error stack:
ERROR: ORA-01034: ORACLE not available
ORA-07318: smsget: open error when opening sgadef.dbf file.
HP-UX Error: 2: No such file or directory
What is the probable cause
The Oracle instance is shutdown that they are trying to access, restart the instance.
52. How can you determine if the SQLNET process is running for SQLNET V1? How about V2
For SQLNET V1 check for the existence of the orasrv process. You can use the command "tcpctl status" to get a full status of the V1 TCPIP server, other protocols have similar command formats. For SQLNET V2 check for the presence of the LISTENER process(s) or you can issue the command "lsnrctl status".
53. What file will give you Oracle instance status information? Where is it located
The alert.ora log. It is located in the directory specified by the background_dump_dest parameter in the v$parameter table.
54. Users aren?t being allowed on the system. The following message is received:
ORA-00257 archiver is stuck. Connect internal only, until freed
What is the problem
The archive destination is probably full, backup the archive logs and remove them and the archiver will re-start.
55. Where would you look to find out if a redo log was corrupted assuming you are using Oracle mirrored redo logs
There is no message that comes to the SQLDBA or SRVMGR programs during startup in this situation, you must check the alert.log file for this information.
56. You attempt to add a datafile and get:
ORA-01118: cannot add anymore datafiles: limit of 40 exceeded
What is the problem and how can you fix it
When the database was created the db_files parameter in the initialization file was set to 40. You can shutdown and reset this to a higher value, up to the value of MAX_DATAFILES as specified at database creation. If the MAX_DATAFILES is set to low, you will have to rebuild the control file to increase it before proceeding.
57. You look at your fragmentation report and see that smon hasn?t coalesced any of you tablespaces, even though you know several have large chunks of contiguous free extents. What is the problem
Check the dba_tablespaces view for the value of pct_increase for the tablespaces. If pct_increase is zero, smon will not coalesce their free space.
58. Your users get the following error:
ORA-00055 maximum number of DML locks exceeded
What is the problem and how do you fix it
The number of DML Locks is set by the initialization parameter DML_LOCKS. If this value is set to low (which it is by default) you will get this error. Increase the value of DML_LOCKS. If you are sure that this is just a temporary problem, you can have them wait and then try again later and the error should clear.
59. You get a call from you backup DBA while you are on vacation. He has corrupted all of the control files while playing with the ALTER DATABASE BACKUP CONTROLFILE command. What do you do
As long as all datafiles are safe and he was successful with the BACKUP controlfile command you can do the following:
CONNECT INTERNAL
STARTUP MOUNT
(Take any read-only tablespaces offline before next step ALTER DATABASE DATAFILE .... OFFLINE;)
RECOVER DATABASE USING BACKUP CONTROLFILE
ALTER DATABASE OPEN RESETLOGS;
(bring read-only tablespaces back online)
Shutdown and backup the system, then restart
If they have a recent output file from the ALTER DATABASE BACKUP CONTROL FILE TO TRACE; command, they can use that to recover as well.
If no backup of the control file is available then the following will be required:
CONNECT INTERNAL
STARTUP NOMOUNT
CREATE CONTROL FILE .....;
However, they will need to know all of the datafiles, logfiles, and settings for MAXLOGFILES, MAXLOGMEMBERS, MAXLOGHISTORY, MAXDATAFILES for the database to use the command.
Tuesday, May 13, 2008
Oracle-Explain the difference between a hot backup and a cold backup and the benefits associated with each.
Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any ball in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any ball in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk
What is Difference Between C/C++
C does not have a class/object concept.C++ provides data abstraction, data encapsulation, Inheritance and Polymorphism.C++ supports all C syntax.In C passing value to a function is "Call by Value" whereas in C++ its "Call by Reference"File extension is .c in C while .cpp in C++.(C++ compiler compiles the files with .c extension but C compiler can not!)In C structures can not have contain functions declarations. In C++ structures are like classes, so declaring functions is legal and allowed.C++ can have inline/virtual functions for the classes.c++ is C with Classes hence C++ while in c the closest u can get to an User defined data type is struct and union
What is the difference between run time binding and compile time binding?
Dynamic Binding :The address of the functions are determined at runtime rather than @ compile time. This is also known as "Late Binding".
Static Binding :The address of the functions are determined at compile time rather than @ run time. This is also known as "Early Binding"
Static Binding :The address of the functions are determined at compile time rather than @ run time. This is also known as "Early Binding"
What are Templates
C++ Templates allow u to generate families of functions or classes that can operate on a variety of different data types, freeing you from the need to create a separate function or class for each type. Using templates, u have the convenience of writing a single generic function or class definition, which the compiler automatically translates into a specific version of the function or class, for each of the different data types that your program actually uses. Many data structures and algorithms can be defined independently of the type of data they work with. You can increase the amount of shared code by separating data-dependent portions from data-independent portions, and templates were introduced to help you do that.
C-What is Operator overloading
When an operator is overloaded, it takes on an additional meaning relative to a certain class. But it can still retain all of its old meanings.Examples:1) The operators >> and << may be used for I/O operations because in the header, they are overloaded.2) In a stack class it is possible to overload the + operator so that it appends the contents of one stack to the contents of another. But the + operator still retains its original meaning relative to other types of data.
What is Polymorphism
'Polymorphism' is an object oriented term. Polymorphism may be defined as the ability of related objects to respond to the same message with different, but appropriate actions. In other words, polymorphism means taking more than one form. Polymorphism leads to two important aspects in Object Oriented terminology - Function Overloading and Function Overriding. Overloading is the practice of supplying more than one definition for a given function name in the same scope. The compiler is left to pick the appropriate version of the function or operator based on the arguments with which it is called. Overriding refers to the modifications made in the sub class to the inherited methods from the base class to change their behavior.
C-C++-interview questions- CPLUS interview Questions
1. Is it possible to have Virtual Constructor? If yes, how? If not, Why not possible ?There is nothing like Virtual Constructor. The Constructor cant be virtual as the constructor is a code which is responsible for creating a instance of a class and it cant be delegated to any other object by virtual keyword means.
2. What about Virtual Destructor?Yes there is a Virtual Destructor. A destructor can be virtual as it is possible as at runtime depending on the type of object baller is balling to , proper destructor will be called.
3. What is Pure Virtual Function? Why and when it is used ?The abstract class whose pure virtual method has to be implemented by all the classes which derive on these. Otherwise it would result in a compilation error.This construct should be used when one wants to ensure that all the derived classes implement the method defined as pure virtual in base class.
4. What is problem with Runtime type identification?The run time type identification comes at a cost of performance penalty. Compiler maintains the class.
5. How Virtual functions call up is maintained?Through Look up tables added by the compile to every class image. This also leads to performance penalty.
6. Can inline functions have a recursion?No.Syntax wise It is allowed. But then the function is no longer Inline. As the compiler will never know how deep the recursion is at compilation time.
7. How do you link a C++ program to C functions?By using the extern "C" linkage specification around the C function declarations.Programmers should know about mangled function names and type-safe linkages. Then they should explain how the extern "C" linkage specification statement turns that feature off during compilation so that the linker properly links function calls to C functions.
8. Explain the scope resolution operator?It permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.
9. How many ways are there to initialize an int with a constant?1. int foo = 123;2. int bar(123);
10. What is your reaction to this line of code? delete this;It is not a good programming Practice.A good programmer will insist that you should absolutely never use the statement if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated. Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the baller can and usually does lead to disaster. I think that the language rules should disallow the idiom, but that's another matter.
11. What is the difference between a copy constructor and an overloaded assignment operator?A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.
12. When should you use multiple inheritance?There are three acceptable answers:- "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."
Consider an Asset class, Building class, Vehicle class, and CompanyCar class. All company cars are vehicles. Some company cars are assets because the organizations own them. Others might be leased. Not all assets are vehicles. Money accounts are assets. Real estate holdings are assets. Some real estate holdings are buildings. Not all buildings are assets. Ad infinitum. When you diagram these relationships, it becomes apparent that multiple inheritance is a likely and intuitive way to model this common problem domain. The applicant should understand, however, that multiple inheritance, like a chainsaw, is a useful tool that has its perils, needs respect, and is best avoided except when nothing else will do.
13. What is a virtual destructor?The simple answer is that a virtual destructor is one that is declared with the virtual attribute.The behavior of a virtual destructor is what is important. If you destroy an object through a baller or reference to a base class, and the base-class destructor is not virtual, the derived-class destructors are not executed, and the destruction might not be comple
14. Can a constructor throw a exception? How to handle the error when the constructor fails?The constructor never throws a error.
15. What are the debugging methods you use when came across a problem?Debugging with tools like :
GDB, DBG, Forte, Visual Studio.
Analyzing the Core dump.
Using tusc to trace the last system call before crash.
Putting Debug statements in the program source code.
16. How the compilers arranges the various sections in the executable image?The executable had following sections:-
Data Section (uninitialized data variable section, initialized data variable section )
Code Section
Remember that all static variables are allocated in the initialized variable section.
17. Explain the ISA and HASA class relationships. How would you implement each in a class design?A specialized class "is" a specialization of another class and, therefore, has the ISA relationship with the other class.This relationship is best implemented by embedding an object of the Salary class in the Employee class.
18. When is a template a better solution than a base class?When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus, the generality) to the designer of the container or manager class.
19. What are the differences between a C++ struct and C++ class?The default member and base-class access specifies are different.This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifies, member functions, overloaded operators, and so on. Actually, the C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base-class inheritance, and a class defaults to the private access specified and private base-class inheritance.
20. How do you know that your class needs a virtual destructor?If your class has at least one virtual function, you should make a destructor for this class virtual. This will allow you to delete a dynamic object through a baller to a base class object. If the destructor is non-virtual, then wrong destructor will be invoked during deletion of the dynamic object.
21. What is the difference between new/delete and malloc/free?Malloc/free do not know about constructors and destructors. New and delete create and destroy objects, while malloc and free allocate and deallocate memory.
22. What happens when a function throws an exception that was not specified by an exception specification for this function?Unexpected() is called, which, by default, will eventually trigger abort().
23. Can you think of a situation where your program would crash without reaching the breakball, which you set at the beginning of main()?C++ allows for dynamic initialization of global variables before main() is invoked. It is possible that initialization of global will invoke some function. If this function crashes the crash will occur before main() is entered.
24. What issue do auto_ptr objects address?If you use auto_ptr objects you would not have to be concerned with heap objects not being deleted even if the exception is thrown.
25. Is there any problem with the following:char *a=NULL; char& p = *a;?The result is undefined. You should never do this. A reference must always refer to some object.
26. Why do C++ compilers need name mangling?Name mangling is the rule according to which C++ changes function's name into function signature before passing that function to a linker. This is how the linker differentiates between different functions with the same name.
27. Is there anything you can do in C++ that you cannot do in C?
No. There is nothing you can do in C++ that you cannot do in C. After all you can write a C++ compiler in C
What are the major differences between C and C++?
What are the differences between new and malloc?
What is the difference between delete and delete[]?
What are the differences between a struct in C and in C++?
What are the advantages/disadvantages of using #define?
What are the advantages/disadvantages of using inline and const?
What is the difference between a baller and a reference?
When would you use a baller? A reference?
What does it mean to take the address of a reference?
What does it mean to declare a function or variable as static?
What is the order of initalization for data?
What is name mangling/name decoration?
What kind of problems does name mangling cause?
How do you work around them?
What is a class?
What are the differences between a struct and a class in C++?
What is the difference between public, private, and protected access?
For class CFoo { }; what default methods will the compiler generate for you>?
How can you force the compiler to not generate them?
What is the purpose of a constructor? Destructor?
What is a constructor initializer list?
When must you use a constructor initializer list?
What is a:
Constructor?
Destructor?
Default constructor?
Copy constructor?
Conversion constructor?
What does it mean to declare a...
member function as virtual?
member function as static?
member function as static?
member variable as static?
destructor as static?
Can you explain the term "resource acquisition is initialization?"
What is a "pure virtual" member function?
What is the difference between public, private, and protected inheritance?
What is virtual inheritance?
What is placement
new?
What is the difference between
operator new
and the
new
operator?
What is exception handling?
Explain what happens when an exception is thrown in C++.
What happens if an exception is not caught?
What happens if an exception is throws from an object's constructor?
What happens if an exception is throws from an object's destructor?
What are the costs and benefits of using exceptions?
When would you choose to return an error code rather than throw an exception?
What is a template?
What is partial specialization or template specialization?
How can you force instantiation of a template?
What is an iterator?
What is an algorithm (in terms of the STL/C++ standard library)?
What is
std::auto_ptr?
What is wrong with this statement?
std::auto_ptr ptr(new char[10]);
It is possible to build a C++ compiler on top of a C compiler. How would you do this?
2. What about Virtual Destructor?Yes there is a Virtual Destructor. A destructor can be virtual as it is possible as at runtime depending on the type of object baller is balling to , proper destructor will be called.
3. What is Pure Virtual Function? Why and when it is used ?The abstract class whose pure virtual method has to be implemented by all the classes which derive on these. Otherwise it would result in a compilation error.This construct should be used when one wants to ensure that all the derived classes implement the method defined as pure virtual in base class.
4. What is problem with Runtime type identification?The run time type identification comes at a cost of performance penalty. Compiler maintains the class.
5. How Virtual functions call up is maintained?Through Look up tables added by the compile to every class image. This also leads to performance penalty.
6. Can inline functions have a recursion?No.Syntax wise It is allowed. But then the function is no longer Inline. As the compiler will never know how deep the recursion is at compilation time.
7. How do you link a C++ program to C functions?By using the extern "C" linkage specification around the C function declarations.Programmers should know about mangled function names and type-safe linkages. Then they should explain how the extern "C" linkage specification statement turns that feature off during compilation so that the linker properly links function calls to C functions.
8. Explain the scope resolution operator?It permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.
9. How many ways are there to initialize an int with a constant?1. int foo = 123;2. int bar(123);
10. What is your reaction to this line of code? delete this;It is not a good programming Practice.A good programmer will insist that you should absolutely never use the statement if the class is to be used by other programmers and instantiated as static, extern, or automatic objects. That much should be obvious.The code has two built-in pitfalls. First, if it executes in a member function for an extern, static, or automatic object, the program will probably crash as soon as the delete statement executes. There is no portable way for an object to tell that it was instantiated on the heap, so the class cannot assert that its object is properly instantiated. Second, when an object commits suicide this way, the using program might not know about its demise. As far as the instantiating program is concerned, the object remains in scope and continues to exist even though the object did itself in. Subsequent dereferencing of the baller can and usually does lead to disaster. I think that the language rules should disallow the idiom, but that's another matter.
11. What is the difference between a copy constructor and an overloaded assignment operator?A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.
12. When should you use multiple inheritance?There are three acceptable answers:- "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."
Consider an Asset class, Building class, Vehicle class, and CompanyCar class. All company cars are vehicles. Some company cars are assets because the organizations own them. Others might be leased. Not all assets are vehicles. Money accounts are assets. Real estate holdings are assets. Some real estate holdings are buildings. Not all buildings are assets. Ad infinitum. When you diagram these relationships, it becomes apparent that multiple inheritance is a likely and intuitive way to model this common problem domain. The applicant should understand, however, that multiple inheritance, like a chainsaw, is a useful tool that has its perils, needs respect, and is best avoided except when nothing else will do.
13. What is a virtual destructor?The simple answer is that a virtual destructor is one that is declared with the virtual attribute.The behavior of a virtual destructor is what is important. If you destroy an object through a baller or reference to a base class, and the base-class destructor is not virtual, the derived-class destructors are not executed, and the destruction might not be comple
14. Can a constructor throw a exception? How to handle the error when the constructor fails?The constructor never throws a error.
15. What are the debugging methods you use when came across a problem?Debugging with tools like :
GDB, DBG, Forte, Visual Studio.
Analyzing the Core dump.
Using tusc to trace the last system call before crash.
Putting Debug statements in the program source code.
16. How the compilers arranges the various sections in the executable image?The executable had following sections:-
Data Section (uninitialized data variable section, initialized data variable section )
Code Section
Remember that all static variables are allocated in the initialized variable section.
17. Explain the ISA and HASA class relationships. How would you implement each in a class design?A specialized class "is" a specialization of another class and, therefore, has the ISA relationship with the other class.This relationship is best implemented by embedding an object of the Salary class in the Employee class.
18. When is a template a better solution than a base class?When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus, the generality) to the designer of the container or manager class.
19. What are the differences between a C++ struct and C++ class?The default member and base-class access specifies are different.This is one of the commonly misunderstood aspects of C++. Believe it or not, many programmers think that a C++ struct is just like a C struct, while a C++ class has inheritance, access specifies, member functions, overloaded operators, and so on. Actually, the C++ struct has all the features of the class. The only differences are that a struct defaults to public member access and public base-class inheritance, and a class defaults to the private access specified and private base-class inheritance.
20. How do you know that your class needs a virtual destructor?If your class has at least one virtual function, you should make a destructor for this class virtual. This will allow you to delete a dynamic object through a baller to a base class object. If the destructor is non-virtual, then wrong destructor will be invoked during deletion of the dynamic object.
21. What is the difference between new/delete and malloc/free?Malloc/free do not know about constructors and destructors. New and delete create and destroy objects, while malloc and free allocate and deallocate memory.
22. What happens when a function throws an exception that was not specified by an exception specification for this function?Unexpected() is called, which, by default, will eventually trigger abort().
23. Can you think of a situation where your program would crash without reaching the breakball, which you set at the beginning of main()?C++ allows for dynamic initialization of global variables before main() is invoked. It is possible that initialization of global will invoke some function. If this function crashes the crash will occur before main() is entered.
24. What issue do auto_ptr objects address?If you use auto_ptr objects you would not have to be concerned with heap objects not being deleted even if the exception is thrown.
25. Is there any problem with the following:char *a=NULL; char& p = *a;?The result is undefined. You should never do this. A reference must always refer to some object.
26. Why do C++ compilers need name mangling?Name mangling is the rule according to which C++ changes function's name into function signature before passing that function to a linker. This is how the linker differentiates between different functions with the same name.
27. Is there anything you can do in C++ that you cannot do in C?
No. There is nothing you can do in C++ that you cannot do in C. After all you can write a C++ compiler in C
What are the major differences between C and C++?
What are the differences between new and malloc?
What is the difference between delete and delete[]?
What are the differences between a struct in C and in C++?
What are the advantages/disadvantages of using #define?
What are the advantages/disadvantages of using inline and const?
What is the difference between a baller and a reference?
When would you use a baller? A reference?
What does it mean to take the address of a reference?
What does it mean to declare a function or variable as static?
What is the order of initalization for data?
What is name mangling/name decoration?
What kind of problems does name mangling cause?
How do you work around them?
What is a class?
What are the differences between a struct and a class in C++?
What is the difference between public, private, and protected access?
For class CFoo { }; what default methods will the compiler generate for you>?
How can you force the compiler to not generate them?
What is the purpose of a constructor? Destructor?
What is a constructor initializer list?
When must you use a constructor initializer list?
What is a:
Constructor?
Destructor?
Default constructor?
Copy constructor?
Conversion constructor?
What does it mean to declare a...
member function as virtual?
member function as static?
member function as static?
member variable as static?
destructor as static?
Can you explain the term "resource acquisition is initialization?"
What is a "pure virtual" member function?
What is the difference between public, private, and protected inheritance?
What is virtual inheritance?
What is placement
new?
What is the difference between
operator new
and the
new
operator?
What is exception handling?
Explain what happens when an exception is thrown in C++.
What happens if an exception is not caught?
What happens if an exception is throws from an object's constructor?
What happens if an exception is throws from an object's destructor?
What are the costs and benefits of using exceptions?
When would you choose to return an error code rather than throw an exception?
What is a template?
What is partial specialization or template specialization?
How can you force instantiation of a template?
What is an iterator?
What is an algorithm (in terms of the STL/C++ standard library)?
What is
std::auto_ptr?
What is wrong with this statement?
std::auto_ptr ptr(new char[10]);
It is possible to build a C++ compiler on top of a C compiler. How would you do this?
Thursday, April 17, 2008
Graph Matrix
A graph matrix is a square matrix whose size is equivalent to the number of nodes in the flow graph. Each row and column correspond to a particular node and the matrix corresponds to the connections (edges) between nodes. By adding a link weight to each matrix entry, more information about the control flow can be captured. In its simplest form, the link weight is 1 if an edge exists and 0 if it does not. But other types of link weights can be represented:1. the probability that an edge will be executed,2. the processing time expended during link traversal,3. the memory required during link traversal, or 4. the resources required during link traversal.Graph theory algorithms can be applied to these graph matrices to help in the analysis necessary to produce the basis set.
Syntax Testing
In syntax testing, the test-cases, i.e. the input to the software, are created based on the specifications of languages understood by the interfaces of a software. Interfaces have many formats: command-line prompts, files, environment variables, pipes, sockets, etc. An interface has a language which defines what legal input to the interface is and what is not. This language may be hidden or open. The existence of a hidden language is not explicitly realised by developers of the software, but a piece of software might nevertheless read some input data, parse it, and act accordingly. In a broader sense, hidden languages exist also in data structures used to transfer information from a software module to another. An open language is appropriately specified in the software documentation.
The motivation for syntax testing springs from the fact that each interface has a language, whether it is hidden or open, from which effective tests can be created with a relatively small effort. Syntax testing is more likely to find faults from the portions of software responsible for hidden language handling, because open languages must have been explicitly considered by the programmer and thus the input handling portion is likely to be better.
Automated syntax testing requires a formal description of the input language in machine readable format. If the language is hidden, the tester must create a specification for it. Common choices are BNF (Backus-Naur form) and regular expressions. Both are notations to define context-free grammar languages. A sentence is a sequence of bytes which are arranged according to the rules of the language. Context-free languages have traditionally been used in compilers of various sorts to create parsers for input sentences. In syntax testing, a context-free language is the base used to generate sentences. These sentences are then fed, or injected, into the software being tested to see if it accepts them, rejects them or fails to process them altogether.
The selection of test-cases in syntax testing could start with single-error sentences. This is likely to reveal most faults assuming the faults are mutually independent and a fault is triggered by one error in a sentence. After all the sentences with one error are tried, the testing proceeds to pairs of errors, three error combinations, and so on. The number of test-cases grows exponentially by the number of combined errors. Several different kinds of errors can be produced in syntax testing:
Syntax errors
Syntax errors violate the grammar of the underlying language. They are created by removing an element, adding an extra element and providing the elements in wrong order. Syntax errors can exist on different levels in the grammar hierarchy: top-level, intermediate-level and field-level.
Delimiter errors
Delimiters mark the separation of fields in a sentence. In ASCII-coded languages the fields are normally characters and letters, and delimiter are white space characters (space, tab, line-feed, etc.), or other delimiters characters (commas, semicolons, etc.) or their combinations. Delimiters can be omitted, multiplied or replaced by other unusual characters. Paired delimiters, such as braces, can be left unbalanced.
Field-value errors
A field-value error is an illegal field in a sentence. Normally, a field value has a range or many disjoint ranges of allowable values. Field errors can include values which are one-below, one-above and totally out-of-range. Values exactly at the range boundary should also be checked.
Context-dependent errors
A context-dependent error violates some property of a sentence which cannot, in practice, be described by context-free grammar.
State dependency error
Not all sentences are acceptable in every possible state of a software component. A state dependency error is generated by inputting a correct sentence during an incorrect state.
Automatic generation of sentences leads to automatic test design where test-cases are designed by a computer. It is suitable, for example, for stress testing, where software is fed with a large amount of input data.
The motivation for syntax testing springs from the fact that each interface has a language, whether it is hidden or open, from which effective tests can be created with a relatively small effort. Syntax testing is more likely to find faults from the portions of software responsible for hidden language handling, because open languages must have been explicitly considered by the programmer and thus the input handling portion is likely to be better.
Automated syntax testing requires a formal description of the input language in machine readable format. If the language is hidden, the tester must create a specification for it. Common choices are BNF (Backus-Naur form) and regular expressions. Both are notations to define context-free grammar languages. A sentence is a sequence of bytes which are arranged according to the rules of the language. Context-free languages have traditionally been used in compilers of various sorts to create parsers for input sentences. In syntax testing, a context-free language is the base used to generate sentences. These sentences are then fed, or injected, into the software being tested to see if it accepts them, rejects them or fails to process them altogether.
The selection of test-cases in syntax testing could start with single-error sentences. This is likely to reveal most faults assuming the faults are mutually independent and a fault is triggered by one error in a sentence. After all the sentences with one error are tried, the testing proceeds to pairs of errors, three error combinations, and so on. The number of test-cases grows exponentially by the number of combined errors. Several different kinds of errors can be produced in syntax testing:
Syntax errors
Syntax errors violate the grammar of the underlying language. They are created by removing an element, adding an extra element and providing the elements in wrong order. Syntax errors can exist on different levels in the grammar hierarchy: top-level, intermediate-level and field-level.
Delimiter errors
Delimiters mark the separation of fields in a sentence. In ASCII-coded languages the fields are normally characters and letters, and delimiter are white space characters (space, tab, line-feed, etc.), or other delimiters characters (commas, semicolons, etc.) or their combinations. Delimiters can be omitted, multiplied or replaced by other unusual characters. Paired delimiters, such as braces, can be left unbalanced.
Field-value errors
A field-value error is an illegal field in a sentence. Normally, a field value has a range or many disjoint ranges of allowable values. Field errors can include values which are one-below, one-above and totally out-of-range. Values exactly at the range boundary should also be checked.
Context-dependent errors
A context-dependent error violates some property of a sentence which cannot, in practice, be described by context-free grammar.
State dependency error
Not all sentences are acceptable in every possible state of a software component. A state dependency error is generated by inputting a correct sentence during an incorrect state.
Automatic generation of sentences leads to automatic test design where test-cases are designed by a computer. It is suitable, for example, for stress testing, where software is fed with a large amount of input data.
Cause Effect Graph
A cause-effect graph is a directed graph that maps a set of causes to a set of effects. The causes may be thought of as the input to the program, and the effects may be thought of as the output. Usually the graph shows the nodes representing the causes on the left side and the nodes representing the effects on the right side. There may be intermediate nodes in between that combine inputs using logical operators such as AND and OR.
Constraints may be added to the causes and effects. These are represented as edges labelled with the constraint symbol using a dashed line. For causes, valid constraint symbols are E (exclusive?), O (one and only one?), and I (at least one?). For effects, valid constraint symbols are R (Require?) and M (Mask?). (This information needs to be verified.)
The graph's direction is as follows: (XXX: a figure would represent this better)Causes --> intermediate nodes --> Effects
Constraints may be added to the causes and effects. These are represented as edges labelled with the constraint symbol using a dashed line. For causes, valid constraint symbols are E (exclusive?), O (one and only one?), and I (at least one?). For effects, valid constraint symbols are R (Require?) and M (Mask?). (This information needs to be verified.)
The graph's direction is as follows: (XXX: a figure would represent this better)Causes --> intermediate nodes --> Effects
Testing Methodologies - Software testing methodology
Testing methodologies are set of rules or guidelines that are followed to minimize the number of test cases and also provide with maximum test coverage
The following methods are commonly used:
· equivalence partioning
· boundary-value analysis
· error guessing
The following are lesser-used methods:
· cause-effect graphing
· syntax testing
· state transition testing
· graph matrix
Equivalence partitioning
Equivalence partitioning is a systematic process that identifies, on the basis of whatever information is available, a set of interesting classes of input conditions to be tested, where each class is representative of (or covers) a large set of other possible tests. If partitioning is applied to the product under test, the product is going to behave in much the same way for all members of the class.
The aim is to minimize the number of test cases required to cover these input conditions.
There are two distinct steps. The first is to identify the equivalence classes (ECs) and the second is to identify the test cases.
(1) Identifying equivalence classes
For each external input:
(i) If the input specifies a range of valid values, define one valid EC (within the range) and two invalid Ecs (one outside each end of the range).
Example: If the input requires a month in the range of 1-12, define one valid EC for months 1 through 12 and two invalid ECs (month<1>12).
(ii) If the input specifies the number (N) of valid values, define one valid EC and two invalid ECs (none, and more than N).
Example: If the input requires the titles of at least three but no more than eight books, then define one valid EC and two invalid ECs (<3>8 books).
(iii) If the input specifies a set of valid values, define one valid EC (within the set) and one invalid EC (outside the set).
Example: If the input requires one of the names TOM, DICK, or HARRY, then define one valid EC (using one of the valid names) and one invalid EC (using the name JOE).
(iv) If there is reason to believe that the program handles each valid input differently, then define one valid EC per valid input.
(v) If the input specifies a “must be” situation, define one valid EC and one invalid EC.
Example: If the first character of the input must be numeric, then define one valid EC where the first character is a number and one invalid EC where the first character is not a number.
(vi) If there is reason to believe that elements in an EC are not handled in an identical manner by the program, subdivide the EC into smaller ECs.
(2) Identifying test cases
(i) Assign a unique number to each EC.
(ii) Until all valid ECs have been covered by test cases, write a new test case covering as many of the uncovered ECs as possible.
(iii) Until all invalid Ecs have been covered by test cases, write a test case that covers one, and only one, of the uncovered invalid ECs.
(iv) If multiple invalid ECs are tested in the same test case, some of those tests may never be executed because the first test may mask other tests or terminate execution of the test case.
Equivalence partitioning significantly reduces the number of input conditions to be tested by identifying classes of conditions that are equivalent to many other conditions. It does not test combinations of input conditions.
Boundary-value analysis
Boundary-value analysis is a variant and refinement of equivalence partitioning, with two major differences:
First, rather than selecting any element in an equivalence class as being representative, elements are selected such that each edge of the EC is the subject of a test. Boundaries are always a good place to look for defects.
Second, rather than focusing exclusively on input conditions, output conditions are also explored by defining output ECs. What can be output? What are the classes of output? What should I create as an input to force a useful set of classes that represent the outputs that ought to be produced?
The guidelines for boundary-value analysis are:
· If an input specifies a range of valid values, write test cases for the ends of the range and invalid-input test cases for conditions just beyond the ends.
Example: If the input requires a real number in the range 0.0 to 90.0 degrees, then write test cases for 0.0, 90.0, -0.001, and 90.001.
· If an input specifies a number of valid values, write test cases for the minimum and maximum number of values and one beneath and beyond these values.
Example: If the input requires the titles of at least 3, but no more than 8, books, then write test cases for 2, 3, 8, and 9 books.
· Use the above guidelines for each output condition.
Boundary-value analysis is not as simple as it sounds, because boundary conditions may be subtle and difficult to identify. The method does not test combinations of input conditions.
Error guessing
Error guessing is an ad hoc approach, based on intuition and experience, to identify tests that are considered likely to expose errors. The basic idea is to make a list of possible errors or error-prone situations and then develop tests based on the list. What are the most common error-prone situations we have seen before? Defects’ histories are useful. There is a high probability that defects that have been there in the past are the kind that are going to be there in the future.
Some items to try are:
· empty or null lists/strings
· zero instances/occurrences
· blanks or null characters in strings
· negative numbers
One of the studies done by Myers (1979) states that the probability of errors remaining in the program is proportional to the number of errors that have been found so far. This alone provides a rich source of focus for productive error guessing.
The following methods are commonly used:
· equivalence partioning
· boundary-value analysis
· error guessing
The following are lesser-used methods:
· cause-effect graphing
· syntax testing
· state transition testing
· graph matrix
Equivalence partitioning
Equivalence partitioning is a systematic process that identifies, on the basis of whatever information is available, a set of interesting classes of input conditions to be tested, where each class is representative of (or covers) a large set of other possible tests. If partitioning is applied to the product under test, the product is going to behave in much the same way for all members of the class.
The aim is to minimize the number of test cases required to cover these input conditions.
There are two distinct steps. The first is to identify the equivalence classes (ECs) and the second is to identify the test cases.
(1) Identifying equivalence classes
For each external input:
(i) If the input specifies a range of valid values, define one valid EC (within the range) and two invalid Ecs (one outside each end of the range).
Example: If the input requires a month in the range of 1-12, define one valid EC for months 1 through 12 and two invalid ECs (month<1>12).
(ii) If the input specifies the number (N) of valid values, define one valid EC and two invalid ECs (none, and more than N).
Example: If the input requires the titles of at least three but no more than eight books, then define one valid EC and two invalid ECs (<3>8 books).
(iii) If the input specifies a set of valid values, define one valid EC (within the set) and one invalid EC (outside the set).
Example: If the input requires one of the names TOM, DICK, or HARRY, then define one valid EC (using one of the valid names) and one invalid EC (using the name JOE).
(iv) If there is reason to believe that the program handles each valid input differently, then define one valid EC per valid input.
(v) If the input specifies a “must be” situation, define one valid EC and one invalid EC.
Example: If the first character of the input must be numeric, then define one valid EC where the first character is a number and one invalid EC where the first character is not a number.
(vi) If there is reason to believe that elements in an EC are not handled in an identical manner by the program, subdivide the EC into smaller ECs.
(2) Identifying test cases
(i) Assign a unique number to each EC.
(ii) Until all valid ECs have been covered by test cases, write a new test case covering as many of the uncovered ECs as possible.
(iii) Until all invalid Ecs have been covered by test cases, write a test case that covers one, and only one, of the uncovered invalid ECs.
(iv) If multiple invalid ECs are tested in the same test case, some of those tests may never be executed because the first test may mask other tests or terminate execution of the test case.
Equivalence partitioning significantly reduces the number of input conditions to be tested by identifying classes of conditions that are equivalent to many other conditions. It does not test combinations of input conditions.
Boundary-value analysis
Boundary-value analysis is a variant and refinement of equivalence partitioning, with two major differences:
First, rather than selecting any element in an equivalence class as being representative, elements are selected such that each edge of the EC is the subject of a test. Boundaries are always a good place to look for defects.
Second, rather than focusing exclusively on input conditions, output conditions are also explored by defining output ECs. What can be output? What are the classes of output? What should I create as an input to force a useful set of classes that represent the outputs that ought to be produced?
The guidelines for boundary-value analysis are:
· If an input specifies a range of valid values, write test cases for the ends of the range and invalid-input test cases for conditions just beyond the ends.
Example: If the input requires a real number in the range 0.0 to 90.0 degrees, then write test cases for 0.0, 90.0, -0.001, and 90.001.
· If an input specifies a number of valid values, write test cases for the minimum and maximum number of values and one beneath and beyond these values.
Example: If the input requires the titles of at least 3, but no more than 8, books, then write test cases for 2, 3, 8, and 9 books.
· Use the above guidelines for each output condition.
Boundary-value analysis is not as simple as it sounds, because boundary conditions may be subtle and difficult to identify. The method does not test combinations of input conditions.
Error guessing
Error guessing is an ad hoc approach, based on intuition and experience, to identify tests that are considered likely to expose errors. The basic idea is to make a list of possible errors or error-prone situations and then develop tests based on the list. What are the most common error-prone situations we have seen before? Defects’ histories are useful. There is a high probability that defects that have been there in the past are the kind that are going to be there in the future.
Some items to try are:
· empty or null lists/strings
· zero instances/occurrences
· blanks or null characters in strings
· negative numbers
One of the studies done by Myers (1979) states that the probability of errors remaining in the program is proportional to the number of errors that have been found so far. This alone provides a rich source of focus for productive error guessing.
Types of software Testing
There are many types of testing. Generally it is classified as White box testing and Black box testing.
White Box Testing
Testing of a function with knowing internal structure of the program. Also known as glass box, structural, clear box and open box testing. A software testing technique whereby explicit knowledge of the internal workings of the item being tested are used to select the test data. Unlike black box testing, white box testing uses specific knowledge of programming code to examine outputs. The test is accurate only if the tester knows what the program is supposed to do. He or she can then see if the program diverges from its intended goal. White box testing does not account for errors caused by omission, and all visible code must also be readable.
Black Box Testing
Testing of a function without knowing internal structure of the program. Black-box and white-box are test design methods. Black-box test design treats the system as a "black-box", so it doesn't explicitly use knowledge of the internal structure. Black-box test design is usually described as focusing on testing functional requirements. Synonyms for black-box include: behavioral, functional, opaque-box, and closed-box. White-box test design allows one to peek inside the "box", and it focuses specifically on using internal knowledge of the software to guide the selection of test data. Synonyms for white-box include: structural, glass-box and clear-box. While black-box and white-box are terms that are still in popular use, many people prefer the terms "behavioral" and "structural". Behavioral test design is slightly different from black-box test design because the use of internal knowledge isn't strictly forbidden, but it's still discouraged. In practice, it hasn't proven useful to use a single test design method. One has to use a mixture of different methods so that they aren't hindered by the limitations of a particular one. Some call this "gray-box" or "translucent-box" test design, but others wish we'd stop talking about boxes altogether.
Black Box Testing Types
Unit Testing
In computer programming, a unit test is a method of testing the correctness of a particular module of source code. The idea is to write test cases for every non-trivial function or method in the module so that each test case is separate from the others if possible. It is the first test in the development process. The source code is normally divided into modules, which in turn are divided into smaller units called units. These units have specific behavior. The test done on these units of code is called unit test. It is important to realize that unit-testing will not catch every error in the program. By definition, it only tests the functionality of the units themselves. Therefore, it will not catch integration errors, performance problems and any other system-wide issues. In addition, it may not be trivial to anticipate all special cases of input the program unit under study may receive in reality. Unit testing is only effective if it is used in conjunction with other software testing activities.
Integration Testing Integration testing is the phase of software testing in which individual software modules are combined and tested as a group. It follows unit testing and precedes system testing. It takes as its input modules that have been checked out by unit testing, groups them in larger aggregates, applies tests defined in an Integration test plan to those aggregates, and delivers as its output the integrated system ready for system testing. The overall idea, is the "building block" approach in which verified assemblages are added to a verified base which is then used to support the Integration testing of further assemblages. System Testing
System testing is a type of testing where the testing environment is same as that of the production environment. It can be done only when all the integrated modules work fine without bugs. As a rule, System testing takes, as its input, all of the "integrated" software components that have successfully passed Integration testing and also the software system itself integrated with any applicable hardware systems. The purpose of Integration testing is to detect any inconsistencies between the software units that are integrated together called assemblages or between any of the assemblages and hardware. System testing is more of a limiting type of testing, where it seeks to detect both defects within the "inter-assemblages" and also the system as a whole.
Performance Testing Performance testing is a testing that is performed to determine how fast some aspect of a system performs under a particular workload. Performance testing can serve different purposes. It can demonstrate that the system meets performance criteria. It can compare two systems to find which performs better. Or it can measure what parts of the system or workload cause the system to perform badly. In the diagnostic case, software engineers use performance tools such as Mercury Load runner, Empirix e-load to measure what parts of a device or software contribute most to the poor performance or to establish throughput levels (and thresholds) for maintained acceptable response time. In performance testing, it is often crucial (and often difficult to arrange) for the test conditions to be similar to the expected actual use. Performance testing technology employs one or more PCs to act as injectors – each emulating the presence or numbers of users and each running an automated sequence of interactions (recorded as a script, or as a series of scripts to emulate different types of user interaction) with the host whose performance is being tested. Usually, a separate PC acts as a test conductor, coordinating and gathering metrics from each of the injectors and collating performance data for reporting purposes. The usual sequence is to ramp up the load – starting with a small number of virtual users and increasing the number over a period to some maximum. Performance testing is of various types:
1. Load Testing: It is the testing of an application by applying varying loads. The intention is to find the breaking point of the application where it crashes. The load is applied in multiple factors.
2. Stress Testing: It is a form of testing that is used to determine the stability of a given system or entity. It involves testing beyond normal operational capacity, often to a breaking point, in order to observe the results. For example, a web server may be stress tested using scripts, bots, and various denial of service tools to observe the performance of a web site during peak loads. Stress testing a subset of load testing.
3. Soak Testing: It is a kind of testing where an application under test is put under load over a period of time say 48 to 72 hours to check the stability. Generally there can be memory overflow problem if the session connection is not cleaned from the memory.
4. Volume Testing: It is similar to stress testing but generally done for stand alone application where we check for the system by sending huge volume of data across the system. For example if we consider any banking applications, a back up is created for every 5 seconds to avoid crashing of the data. The data from one system is transferred to another system through an intermediate system which monitors the performance of the transfer and also the speed of transfer.
White Box Testing
Testing of a function with knowing internal structure of the program. Also known as glass box, structural, clear box and open box testing. A software testing technique whereby explicit knowledge of the internal workings of the item being tested are used to select the test data. Unlike black box testing, white box testing uses specific knowledge of programming code to examine outputs. The test is accurate only if the tester knows what the program is supposed to do. He or she can then see if the program diverges from its intended goal. White box testing does not account for errors caused by omission, and all visible code must also be readable.
Black Box Testing
Testing of a function without knowing internal structure of the program. Black-box and white-box are test design methods. Black-box test design treats the system as a "black-box", so it doesn't explicitly use knowledge of the internal structure. Black-box test design is usually described as focusing on testing functional requirements. Synonyms for black-box include: behavioral, functional, opaque-box, and closed-box. White-box test design allows one to peek inside the "box", and it focuses specifically on using internal knowledge of the software to guide the selection of test data. Synonyms for white-box include: structural, glass-box and clear-box. While black-box and white-box are terms that are still in popular use, many people prefer the terms "behavioral" and "structural". Behavioral test design is slightly different from black-box test design because the use of internal knowledge isn't strictly forbidden, but it's still discouraged. In practice, it hasn't proven useful to use a single test design method. One has to use a mixture of different methods so that they aren't hindered by the limitations of a particular one. Some call this "gray-box" or "translucent-box" test design, but others wish we'd stop talking about boxes altogether.
Black Box Testing Types
Unit Testing
In computer programming, a unit test is a method of testing the correctness of a particular module of source code. The idea is to write test cases for every non-trivial function or method in the module so that each test case is separate from the others if possible. It is the first test in the development process. The source code is normally divided into modules, which in turn are divided into smaller units called units. These units have specific behavior. The test done on these units of code is called unit test. It is important to realize that unit-testing will not catch every error in the program. By definition, it only tests the functionality of the units themselves. Therefore, it will not catch integration errors, performance problems and any other system-wide issues. In addition, it may not be trivial to anticipate all special cases of input the program unit under study may receive in reality. Unit testing is only effective if it is used in conjunction with other software testing activities.
Integration Testing Integration testing is the phase of software testing in which individual software modules are combined and tested as a group. It follows unit testing and precedes system testing. It takes as its input modules that have been checked out by unit testing, groups them in larger aggregates, applies tests defined in an Integration test plan to those aggregates, and delivers as its output the integrated system ready for system testing. The overall idea, is the "building block" approach in which verified assemblages are added to a verified base which is then used to support the Integration testing of further assemblages. System Testing
System testing is a type of testing where the testing environment is same as that of the production environment. It can be done only when all the integrated modules work fine without bugs. As a rule, System testing takes, as its input, all of the "integrated" software components that have successfully passed Integration testing and also the software system itself integrated with any applicable hardware systems. The purpose of Integration testing is to detect any inconsistencies between the software units that are integrated together called assemblages or between any of the assemblages and hardware. System testing is more of a limiting type of testing, where it seeks to detect both defects within the "inter-assemblages" and also the system as a whole.
Performance Testing Performance testing is a testing that is performed to determine how fast some aspect of a system performs under a particular workload. Performance testing can serve different purposes. It can demonstrate that the system meets performance criteria. It can compare two systems to find which performs better. Or it can measure what parts of the system or workload cause the system to perform badly. In the diagnostic case, software engineers use performance tools such as Mercury Load runner, Empirix e-load to measure what parts of a device or software contribute most to the poor performance or to establish throughput levels (and thresholds) for maintained acceptable response time. In performance testing, it is often crucial (and often difficult to arrange) for the test conditions to be similar to the expected actual use. Performance testing technology employs one or more PCs to act as injectors – each emulating the presence or numbers of users and each running an automated sequence of interactions (recorded as a script, or as a series of scripts to emulate different types of user interaction) with the host whose performance is being tested. Usually, a separate PC acts as a test conductor, coordinating and gathering metrics from each of the injectors and collating performance data for reporting purposes. The usual sequence is to ramp up the load – starting with a small number of virtual users and increasing the number over a period to some maximum. Performance testing is of various types:
1. Load Testing: It is the testing of an application by applying varying loads. The intention is to find the breaking point of the application where it crashes. The load is applied in multiple factors.
2. Stress Testing: It is a form of testing that is used to determine the stability of a given system or entity. It involves testing beyond normal operational capacity, often to a breaking point, in order to observe the results. For example, a web server may be stress tested using scripts, bots, and various denial of service tools to observe the performance of a web site during peak loads. Stress testing a subset of load testing.
3. Soak Testing: It is a kind of testing where an application under test is put under load over a period of time say 48 to 72 hours to check the stability. Generally there can be memory overflow problem if the session connection is not cleaned from the memory.
4. Volume Testing: It is similar to stress testing but generally done for stand alone application where we check for the system by sending huge volume of data across the system. For example if we consider any banking applications, a back up is created for every 5 seconds to avoid crashing of the data. The data from one system is transferred to another system through an intermediate system which monitors the performance of the transfer and also the speed of transfer.
What if there isn't enough time for thorough testing?
Use risk analysis to determine where testing should be focused.Since it's rarely possible to test every possible aspect of an application, every possible combination of events, every dependency, or everything that could go wrong, risk analysis is appropriate to most software development projects. This requires judgement skills, common sense, and experience. (If warranted, formal methods are also available.) Considerations can include:
• Which functionality is most important to the project's intended purpose? • Which functionality is most visible to the user? • Which functionality has the largest safety impact? • Which functionality has the largest financial impact on users? • Which aspects of the application are most important to the customer? • Which aspects of the application can be tested early in the development cycle? • Which parts of the code are most complex, and thus most subject to errors? • Which parts of the application were developed in rush or panic mode? • Which aspects of similar/related previous projects caused problems? • Which aspects of similar/related previous projects had large maintenance expenses? • Which parts of the requirements and design are unclear or poorly thought out? • What do the developers think are the highest-risk aspects of the application? • What kinds of problems would cause the worst publicity? • What kinds of problems would cause the most customer service complaints? • What kinds of tests could easily cover multiple functionalities? • Which tests will have the best high-risk-coverage to time-required ratio?
• Which functionality is most important to the project's intended purpose? • Which functionality is most visible to the user? • Which functionality has the largest safety impact? • Which functionality has the largest financial impact on users? • Which aspects of the application are most important to the customer? • Which aspects of the application can be tested early in the development cycle? • Which parts of the code are most complex, and thus most subject to errors? • Which parts of the application were developed in rush or panic mode? • Which aspects of similar/related previous projects caused problems? • Which aspects of similar/related previous projects had large maintenance expenses? • Which parts of the requirements and design are unclear or poorly thought out? • What do the developers think are the highest-risk aspects of the application? • What kinds of problems would cause the worst publicity? • What kinds of problems would cause the most customer service complaints? • What kinds of tests could easily cover multiple functionalities? • Which tests will have the best high-risk-coverage to time-required ratio?
How can it be known when to stop testing?
This can be difficult to determine. Many modern software applications are so complex, and run in such an interdependent environment, that complete testing can never be done. Common factors in deciding when to stop are: • Deadlines (release deadlines, testing deadlines, etc.) • Test cases completed with certain percentage passed • Test budget depleted • Coverage of code/functionality/requirements reaches a specified point • Bug rate falls below a certain level • Beta or alpha testing period end
What's a 'test case'?
A test case is a document that describes an input, action, or event and an expected response, to determine if a feature of an application is working correctly. A test case should contain particulars such as test case identifier, test case name, objective, test conditions/setup, input data requirements, steps, and expected results.
Note that the process of developing test cases can help find problems in the requirements or design of an application, since it requires completely thinking through the operation of the application. For this reason, it's useful to prepare test cases early in the development cycle if possible
Note that the process of developing test cases can help find problems in the requirements or design of an application, since it requires completely thinking through the operation of the application. For this reason, it's useful to prepare test cases early in the development cycle if possible
What's a 'test plan ?
A software project test plan is a document that describes the objectives, scope, approach, and focus of a software testing effort. The process of preparing a test plan is a useful way to think through the efforts needed to validate the acceptability of a software product. The completed document will help people outside the test group understand the 'why' and 'how' of product validation. It should be thorough enough to be useful but not so thorough that no one outside the test group will read it. The following are some of the items that might be included in a test plan, depending on the particular project: • Title • Identification of software including version/release numbers • Revision history of document including authors, dates, approvals • Table of Contents • Purpose of document, intended audience • Objective of testing effort • Software product overview • Relevant related document list, such as requirements, design documents, other test plans, etc. • Relevant standards or legal requirements • Traceability requirements • Relevant naming conventions and identifier conventions • Overall software project organization and personnel/contact-info/responsibilties • Test organization and personnel/contact-info/responsibilities • Assumptions and dependencies • Project risk analysis • Testing priorities and focus • Scope and limitations of testing • Test outline - a decomposition of the test approach by test type, feature, functionality, process, system, module, etc. as applicable • Outline of data input equivalence classes, boundary value analysis, error classes • Test environment - hardware, operating systems, other required software, data configurations, interfaces to other systems • Test environment validity analysis - differences between the test and production systems and their impact on test validity. • Test environment setup and configuration issues • Software migration processes • Software CM processes • Test data setup requirements • Database setup requirements • Outline of system-logging/error-logging/other capabilities, and tools such as screen capture software, that will be used to help describe and report bugs • Discussion of any specialized software or hardware tools that will be used by testers to help track the cause or source of bugs • Test automation - justification and overview • Test tools to be used, including versions, patches, etc. • Test script/test code maintenance processes and version control • Problem tracking and resolution - tools and processes • Project test metrics to be used • Reporting requirements and testing deliverables • Software entrance and exit criteria • Initial sanity testing period and criteria • Test suspension and restart criteria • Personnel allocation • Personnel pre-training needs • Test site/location • Outside test organizations to be utilized and their purpose, responsibilties, deliverables, contact persons, and coordination issues • Relevant proprietary, classified, security, and licensing issues. • Open issues • Appendix - glossary, acronyms, etc.
Friday, January 11, 2008
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