51. What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold
on the the constraint can be enforced by simply enforcing the domain constraint and
key constraint on the relation.
52. What are partial, alternate,, artificial, compound and natural key?
Partial Key:
It is a set of attributes that can uniquely identify weak entities and that are related
to same owner entity. It is sometime called as Discriminator.
Alternate Key:
All Candidate Keys excluding the Primary Key are known as Alternate Keys.
Artificial Key:
If no obvious key, either stand alone or compound is available, then the last resort is
to simply create a key, by assigning a unique number to each record or occurrence.
Then this is known as developing an artificial key.
Compound Key:
If no single data element uniquely identifies occurrences within a construct, then
combining multiple elements to create a unique identifier for the construct is known
as creating a compound key.
Natural Key:
When one of the data elements stored within a construct is utilized as the primary
key, then it is called the natural key.
53. What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:
Ø Binary search style indexing
Ø B-Tree indexing
Ø Inverted list indexing
Ø Memory resident table
Ø Table indexing
54. What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about
every relation and index that it contains. This information is stored in a collection of
relations maintained by the system called metadata. It is also called data dictionary.
55. What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has
the least estimated cost is referred to as query optimization.
56. What is join dependency and inclusion dependency?
Join Dependency:
A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ...,
Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join
decomposition of R . There is no set of sound and complete inference rules for JD.
Inclusion Dependency:
An Inclusion Dependency is a statement of the form that some columns of a relation
are contained in other columns. A foreign key constraint is an example of inclusion
dependency.
57. What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its
effects should persist even if the system crashes before all its changes are reflected
on disk. This property is called durability.
58. What do you mean by atomicity and aggregation?
Atomicity:
Either all actions are carried out or none are. Users should not have to worry about
the effect of incomplete transactions. DBMS ensures this by undoing the actions of
incomplete transactions.
Aggregation:
A concept which is used to model a relationship between a collection of entities and
relationships. It is used when we need to express a relationship among relationships.
59. What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might
cause the deadlock detection algorithms to identify deadlocks that do not really exist.
Such situations are called phantom deadlocks and they lead to unnecessary aborts.
60. What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS
can reduce the amount of work to be done during restart in the event of subsequent
crashes.
61. What are the different phases of transaction?
Different phases are
Ø Analysis phase
Ø Redo Phase
Ø Undo phase
62. What do you mean by flat file database?
It is a database in which there are no programs or user access languages. It has no
cross-file capabilities but is user-friendly and provides user-interface management.
63. What is "transparent DBMS"?
It is one, which keeps its Physical Structure hidden from user.
64. Brief theory of Network, Hierarchical schemas and their properties
Network schema uses a graph data structure to organize records example for such a
database management system is CTCG while a hierarchical schema uses a tree data
structure example for such a system is IMS.
65. What is a query?
A query with respect to DBMS relates to user commands that are used to interact
with a data base. The query language can be classified into data definition language
and data manipulation language.
66. What do you mean by Correlated subquery?
Subqueries, or nested queries, are used to bring back a set of rows to be used by the
parent query. Depending on how the subquery is written, it can be executed once for
the parent query or it can be executed once for each row returned by the parent
query. If the subquery is executed for each row of the parent, this is called a
correlated subquery.
A correlated subquery can be easily identified if it contains any references to the
parent subquery columns in its WHERE clause. Columns from the subquery cannot be
referenced anywhere else in the parent query. The following example demonstrates a
non-correlated subquery.
E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where
CUST.CNUM = ORDER.CNUM)
67. What are the primitive operations common to all record management systems?
Addition, deletion and modification.
68. Name the buffer in which all the commands that are typed in are stored
‘Edit’ Buffer
69. What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.
70. Are the resulting relations of PRODUCT and JOIN operation the same?
No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.
71. What is RDBMS KERNEL?
Two important pieces of RDBMS architecture are the kernel, which is the software,
and the data dictionary, which consists of the system-level data structures used by
the kernel to manage the database
You might think of an RDBMS as an operating system (or set of subsystems),
designed specifically for controlling data access; its primary functions are storing,
retrieving, and securing data. An RDBMS maintains its own list of authorized users
and their associated privileges; manages memory caches and paging; controls
locking for concurrent resource usage; dispatches and schedules user requests; and
manages space usage within its table-space structures
.
72. Name the sub-systems of a RDBMS
I/O, Security, Language Processing, Process Control, Storage Management, Logging
and Recovery, Distribution Control, Transaction Control, Memory Management, Lock
Management
73. Which part of the RDBMS takes care of the data dictionary? How
Data dictionary is a set of tables and database objects that is stored in a special area
of the database and maintained exclusively by the kernel.
74. What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence of the objects, provides
access to them, and maps the actual physical storage location.
75. Not only RDBMS takes care of locating data it also
determines an optimal access path to store or retrieve the data
76. How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query Language (SQL)
77. Define SQL and state the differences between SQL and other conventional
programming Languages
SQL is a nonprocedural language that is designed specifically for data access
operations on normalized relational database structures. The primary difference
between SQL and other conventional programming languages is that SQL statements
specify what data operations should be performed rather than how to perform them.
78. Name the three major set of files on disk that compose a database in Oracle
There are three major sets of files on disk that compose a database. All the files are
binary. These are
Ø Database files
Ø Control files
Ø Redo logs
The most important of these are the database files where the actual data resides.
The control files and the redo logs support the functioning of the architecture itself.
All three sets of files must be present, open, and available to Oracle for any data on
the database to be useable. Without these files, you cannot access the database, and
the database administrator might have to recover some or all of the database using
a backup, if there is one.
79. What is an Oracle Instance?
The Oracle system processes, also known as Oracle background processes, provide
functions for the user processes—functions that would otherwise be done by the user
processes themselves
Oracle database-wide system memory is known as the SGA, the system global area
or shared global area. The data and control structures in the SGA are shareable, and
all the Oracle background processes and user processes can use them.
The combination of the SGA and the Oracle background processes is known as an
Oracle instance
80. What are the four Oracle system processes that must always be up and running
for the database to be useable
The four Oracle system processes that must always be up and running for the
database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON
(System Monitor), and PMON (Process Monitor).
81. What are database files, control files and log files. How many of these files
should a database have at least? Why?
Database Files
The database files hold the actual data and are typically the largest in size.
Depending on their sizes, the tables (and other objects) for all the user accounts can
go in one database file—but that's not an ideal situation because it does not make
the database structure very flexible for controlling access to storage for different
users, putting the database on different disk drives, or backing up and restoring just
part of the database.
You must have at least one database file but usually, more than one files are used.
In terms of accessing and using the data in the tables and other objects, the number
(or location) of the files is immaterial.
The database files are fixed in size and never grow bigger than the size at which they
were created
Control Files
The control files and redo logs support the rest of the architecture. Any database
must have at least one control file, although you typically have more than one to
guard against loss. The control file records the name of the database, the date and
time it was created, the location of the database and redo logs, and the
synchronization information to ensure that all three sets of files are always in step.
Every time you add a new database or redo log file to the database, the information
is recorded in the control files.
Redo Logs
Any database must have at least two redo logs. These are the journals for the
database; the redo logs record all changes to the user objects or system objects. If
any type of failure occurs, the changes recorded in the redo logs can be used to
bring the database to a consistent state without losing any committed transactions.
In the case of non-data loss failure, Oracle can apply the information in the redo logs
automatically without intervention from the DBA.
The redo log files are fixed in size and never grow dynamically from the size at which
they were created.
82. What is ROWID?
The ROWID is a unique database-wide physical address for every row on every table.
Once assigned (when the row is first inserted into the database), it never changes
until the row is deleted or the table is dropped.
The ROWID consists of the following three components, the combination of which
uniquely identifies the physical storage location of the row.
Ø Oracle database file number, which contains the block with the rows
Ø Oracle block address, which contains the row
Ø The row within the block (because each block can hold many rows)
The ROWID is used internally in indexes as a quick means of retrieving rows with a
particular key value. Application developers also use it in SQL statements as a quick
way to access a row once they know the ROWID
83. What is Oracle Block? Can two Oracle Blocks have the same address?
Oracle "formats" the database files into a number of Oracle blocks when they are
first created—making it easier for the RDBMS software to manage the files and
easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of
the block size, the entire block is not available for holding data; Oracle takes up
some space to manage the contents of the block. This block header has a minimum
size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size
can improve performance, but it should be done only when the database is first
created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two
blocks can have the same block address if they are in different database files.
84. What is database Trigger?
A database trigger is a PL/SQL block that can defined to automatically execute for
insert, update, and delete statements against a table. The trigger can e defined to
execute once for the entire statement or once for every row that is inserted,
updated, or deleted. For any one table, there are twelve events for which you can
define database triggers. A database trigger can call database procedures that are
also written in PL/SQL.
85. Name two utilities that Oracle provides, which are use for backup and recovery.
Along with the RDBMS software, Oracle provides two utilities that you can use to
back up and restore the database. These utilities are Export and Import.
The Export utility dumps the definitions and data for the specified part of the
database to an operating system binary file. The Import utility reads the file
produced by an export, recreates the definitions of objects, and inserts the data
If Export and Import are used as a means of backing up and recovering the
database, all the changes made to the database cannot be recovered since the
export was performed. The best you can do is recover the database to the time when
the export was last performed.
86. What are stored-procedures? And what are the advantages of using them.
Stored procedures are database objects that perform a user defined operation. A
stored procedure can have a set of compound SQL statements. A stored procedure
executes the SQL commands and returns the result to the client. Stored procedures
are used to reduce network traffic.
87. How are exceptions handled in PL/SQL? Give some of the internal exceptions'
name
PL/SQL exception handling is a mechanism for dealing with run-time errors
encountered during procedure execution. Use of this mechanism enables execution
to continue if the error is not severe enough to cause procedure termination.
The exception handler must be defined within a subprogram specification. Errors
cause the program to raise an exception with a transfer of control to the exceptionhandler
block. After the exception handler executes, control returns to the block in
which the handler was defined. If there are no more executable statements in the
block, control returns to the caller.
User-Defined Exceptions
PL/SQL enables the user to define exception handlers in the declarations area of
subprogram specifications. User accomplishes this by naming an exception as in the
following example:
ot_failure EXCEPTION;
In this case, the exception name is ot_failure. Code associated with this handler is
written in the EXCEPTION specification area as follows:
EXCEPTION
when OT_FAILURE then
out_status_code := g_out_status_code;
out_msg := g_out_msg;
The following is an example of a subprogram exception:
EXCEPTION
when NO_DATA_FOUND then
g_out_status_code := 'FAIL';
RAISE ot_failure;
Within this exception is the RAISE statement that transfers control back to the
ot_failure exception handler. This technique of raising the exception is used to invoke
all user-defined exceptions.
System-Defined Exceptions
Exceptions internal to PL/SQL are raised automatically upon error. NO_DATA_FOUND
is a system-defined exception. Table below gives a complete list of internal
exceptions.
PL/SQL internal exceptions.
PL/SQL internal exceptions.
Exception Name Oracle Error
CURSOR_ALREADY_OPEN ORA-06511
DUP_VAL_ON_INDEX ORA-00001
INVALID_CURSOR ORA-01001
INVALID_NUMBER ORA-01722
LOGIN_DENIED ORA-01017
NO_DATA_FOUND ORA-01403
NOT_LOGGED_ON ORA-01012
PROGRAM_ERROR ORA-06501
STORAGE_ERROR ORA-06500
TIMEOUT_ON_RESOURCE ORA-00051
TOO_MANY_ROWS ORA-01422
TRANSACTION_BACKED_OUT ORA-00061
VALUE_ERROR ORA-06502
ZERO_DIVIDE ORA-01476
In addition to this list of exceptions, there is a catch-all exception named OTHERS
that traps all errors for which specific error handling has not been established.
88. Does PL/SQL support "overloading"? Explain
The concept of overloading in PL/SQL relates to the idea that you can define
procedures and functions with the same name. PL/SQL does not look only at the
referenced name, however, to resolve a procedure or function call. The count and
data types of formal parameters are also considered.
PL/SQL also attempts to resolve any procedure or function calls in locally defined
packages before looking at globally defined packages or internal functions. To further
ensure calling the proper procedure, you can use the dot notation. Prefacing a
procedure or function name with the package name fully qualifies any procedure or
function reference.
89. Tables derived from the ERD
a) Are totally unnormalised
b) Are always in 1NF
c) Can be further denormalised
d) May have multi-valued attributes
90. Spurious tuples may occur due to
i. Bad normalization
ii. Theta joins
iii. Updating tables from join
a) i & ii b) ii & iii
c) i & iii d) ii & iii
(a) i & iii because theta joins are joins made on keys that are not primary keys.
91. A B C is a set of attributes. The functional dependency is as follows
AB -> B
AC -> C
C -> B
a) is in 1NF
b) is in 2NF
c) is in 3NF
d) is in BCNF
(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the primary key. Since C B is a FD
given, where neither C is a Key nor B is a prime attribute, this it is not in 3NF.
Further B is not functionally dependent on key AC thus it is not in 2NF. Thus the
given FDs is in 1NF.
92. In mapping of ERD to DFD
a) entities in ERD should correspond to an existing entity/store in DFD
b) entity in DFD is converted to attributes of an entity in ERD
c) relations in ERD has 1 to 1 correspondence to processes in DFD
d) relationships in ERD has 1 to 1 correspondence to flows in DFD
(a) entities in ERD should correspond to an existing entity/store in DFD
93. A dominant entity is the entity
a) on the N side in a 1 : N relationship
b) on the 1 side in a 1 : N relationship
c) on either side in a 1 : 1 relationship
d) nothing to do with 1 : 1 or 1 : N relationship
(b) on the 1 side in a 1 : N relationship
94. Select 'NORTH', CUSTOMER From CUST_DTLS Where REGION = 'N' Order By
CUSTOMER Union Select 'EAST', CUSTOMER From CUST_DTLS Where REGION = 'E'
Order By CUSTOMER
The above is
a) Not an error
b) Error - the string in single quotes 'NORTH' and 'SOUTH'
c) Error - the string should be in double quotes
d) Error - ORDER BY clause
(d) Error - the ORDER BY clause. Since ORDER BY clause cannot be used in UNIONS
95. What is Storage Manager?
It is a program module that provides the interface between the low-level data stored
in database, application programs and queries submitted to the system.
96. What is Buffer Manager?
It is a program module, which is responsible for fetching data from disk storage into
main memory and deciding what data to be cache in memory.
97. What is Transaction Manager?
It is a program module, which ensures that database, remains in a consistent state
despite system failures and concurrent transaction execution proceeds without
conflicting.
98. What is File Manager?
It is a program module, which manages the allocation of space on disk storage and
data structure used to represent information stored on a disk.
99. What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction of integrity constraint and
checks the authority of user to access data.
100. What are stand-alone procedures?
Procedures that are not part of a package are known as stand-alone because they
independently defined. A good example of a stand-alone procedure is one written in
a SQL*Forms application. These types of procedures are not available for reference
from other Oracle tools. Another limitation of stand-alone procedures is that they are
compiled at run time, which slows execution.
A relation is said to be in DKNF if all constraints and dependencies that should hold
on the the constraint can be enforced by simply enforcing the domain constraint and
key constraint on the relation.
52. What are partial, alternate,, artificial, compound and natural key?
Partial Key:
It is a set of attributes that can uniquely identify weak entities and that are related
to same owner entity. It is sometime called as Discriminator.
Alternate Key:
All Candidate Keys excluding the Primary Key are known as Alternate Keys.
Artificial Key:
If no obvious key, either stand alone or compound is available, then the last resort is
to simply create a key, by assigning a unique number to each record or occurrence.
Then this is known as developing an artificial key.
Compound Key:
If no single data element uniquely identifies occurrences within a construct, then
combining multiple elements to create a unique identifier for the construct is known
as creating a compound key.
Natural Key:
When one of the data elements stored within a construct is utilized as the primary
key, then it is called the natural key.
53. What is indexing and what are the different kinds of indexing?
Indexing is a technique for determining how quickly specific data can be found.
Types:
Ø Binary search style indexing
Ø B-Tree indexing
Ø Inverted list indexing
Ø Memory resident table
Ø Table indexing
54. What is system catalog or catalog relation? How is better known as?
A RDBMS maintains a description of all the data that it contains, information about
every relation and index that it contains. This information is stored in a collection of
relations maintained by the system called metadata. It is also called data dictionary.
55. What is meant by query optimization?
The phase that identifies an efficient execution plan for evaluating a query that has
the least estimated cost is referred to as query optimization.
56. What is join dependency and inclusion dependency?
Join Dependency:
A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ...,
Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join
decomposition of R . There is no set of sound and complete inference rules for JD.
Inclusion Dependency:
An Inclusion Dependency is a statement of the form that some columns of a relation
are contained in other columns. A foreign key constraint is an example of inclusion
dependency.
57. What is durability in DBMS?
Once the DBMS informs the user that a transaction has successfully completed, its
effects should persist even if the system crashes before all its changes are reflected
on disk. This property is called durability.
58. What do you mean by atomicity and aggregation?
Atomicity:
Either all actions are carried out or none are. Users should not have to worry about
the effect of incomplete transactions. DBMS ensures this by undoing the actions of
incomplete transactions.
Aggregation:
A concept which is used to model a relationship between a collection of entities and
relationships. It is used when we need to express a relationship among relationships.
59. What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might
cause the deadlock detection algorithms to identify deadlocks that do not really exist.
Such situations are called phantom deadlocks and they lead to unnecessary aborts.
60. What is a checkpoint and When does it occur?
A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS
can reduce the amount of work to be done during restart in the event of subsequent
crashes.
61. What are the different phases of transaction?
Different phases are
Ø Analysis phase
Ø Redo Phase
Ø Undo phase
62. What do you mean by flat file database?
It is a database in which there are no programs or user access languages. It has no
cross-file capabilities but is user-friendly and provides user-interface management.
63. What is "transparent DBMS"?
It is one, which keeps its Physical Structure hidden from user.
64. Brief theory of Network, Hierarchical schemas and their properties
Network schema uses a graph data structure to organize records example for such a
database management system is CTCG while a hierarchical schema uses a tree data
structure example for such a system is IMS.
65. What is a query?
A query with respect to DBMS relates to user commands that are used to interact
with a data base. The query language can be classified into data definition language
and data manipulation language.
66. What do you mean by Correlated subquery?
Subqueries, or nested queries, are used to bring back a set of rows to be used by the
parent query. Depending on how the subquery is written, it can be executed once for
the parent query or it can be executed once for each row returned by the parent
query. If the subquery is executed for each row of the parent, this is called a
correlated subquery.
A correlated subquery can be easily identified if it contains any references to the
parent subquery columns in its WHERE clause. Columns from the subquery cannot be
referenced anywhere else in the parent query. The following example demonstrates a
non-correlated subquery.
E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where
CUST.CNUM = ORDER.CNUM)
67. What are the primitive operations common to all record management systems?
Addition, deletion and modification.
68. Name the buffer in which all the commands that are typed in are stored
‘Edit’ Buffer
69. What are the unary operations in Relational Algebra?
PROJECTION and SELECTION.
70. Are the resulting relations of PRODUCT and JOIN operation the same?
No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.
71. What is RDBMS KERNEL?
Two important pieces of RDBMS architecture are the kernel, which is the software,
and the data dictionary, which consists of the system-level data structures used by
the kernel to manage the database
You might think of an RDBMS as an operating system (or set of subsystems),
designed specifically for controlling data access; its primary functions are storing,
retrieving, and securing data. An RDBMS maintains its own list of authorized users
and their associated privileges; manages memory caches and paging; controls
locking for concurrent resource usage; dispatches and schedules user requests; and
manages space usage within its table-space structures
.
72. Name the sub-systems of a RDBMS
I/O, Security, Language Processing, Process Control, Storage Management, Logging
and Recovery, Distribution Control, Transaction Control, Memory Management, Lock
Management
73. Which part of the RDBMS takes care of the data dictionary? How
Data dictionary is a set of tables and database objects that is stored in a special area
of the database and maintained exclusively by the kernel.
74. What is the job of the information stored in data-dictionary?
The information in the data dictionary validates the existence of the objects, provides
access to them, and maps the actual physical storage location.
75. Not only RDBMS takes care of locating data it also
determines an optimal access path to store or retrieve the data
76. How do you communicate with an RDBMS?
You communicate with an RDBMS using Structured Query Language (SQL)
77. Define SQL and state the differences between SQL and other conventional
programming Languages
SQL is a nonprocedural language that is designed specifically for data access
operations on normalized relational database structures. The primary difference
between SQL and other conventional programming languages is that SQL statements
specify what data operations should be performed rather than how to perform them.
78. Name the three major set of files on disk that compose a database in Oracle
There are three major sets of files on disk that compose a database. All the files are
binary. These are
Ø Database files
Ø Control files
Ø Redo logs
The most important of these are the database files where the actual data resides.
The control files and the redo logs support the functioning of the architecture itself.
All three sets of files must be present, open, and available to Oracle for any data on
the database to be useable. Without these files, you cannot access the database, and
the database administrator might have to recover some or all of the database using
a backup, if there is one.
79. What is an Oracle Instance?
The Oracle system processes, also known as Oracle background processes, provide
functions for the user processes—functions that would otherwise be done by the user
processes themselves
Oracle database-wide system memory is known as the SGA, the system global area
or shared global area. The data and control structures in the SGA are shareable, and
all the Oracle background processes and user processes can use them.
The combination of the SGA and the Oracle background processes is known as an
Oracle instance
80. What are the four Oracle system processes that must always be up and running
for the database to be useable
The four Oracle system processes that must always be up and running for the
database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON
(System Monitor), and PMON (Process Monitor).
81. What are database files, control files and log files. How many of these files
should a database have at least? Why?
Database Files
The database files hold the actual data and are typically the largest in size.
Depending on their sizes, the tables (and other objects) for all the user accounts can
go in one database file—but that's not an ideal situation because it does not make
the database structure very flexible for controlling access to storage for different
users, putting the database on different disk drives, or backing up and restoring just
part of the database.
You must have at least one database file but usually, more than one files are used.
In terms of accessing and using the data in the tables and other objects, the number
(or location) of the files is immaterial.
The database files are fixed in size and never grow bigger than the size at which they
were created
Control Files
The control files and redo logs support the rest of the architecture. Any database
must have at least one control file, although you typically have more than one to
guard against loss. The control file records the name of the database, the date and
time it was created, the location of the database and redo logs, and the
synchronization information to ensure that all three sets of files are always in step.
Every time you add a new database or redo log file to the database, the information
is recorded in the control files.
Redo Logs
Any database must have at least two redo logs. These are the journals for the
database; the redo logs record all changes to the user objects or system objects. If
any type of failure occurs, the changes recorded in the redo logs can be used to
bring the database to a consistent state without losing any committed transactions.
In the case of non-data loss failure, Oracle can apply the information in the redo logs
automatically without intervention from the DBA.
The redo log files are fixed in size and never grow dynamically from the size at which
they were created.
82. What is ROWID?
The ROWID is a unique database-wide physical address for every row on every table.
Once assigned (when the row is first inserted into the database), it never changes
until the row is deleted or the table is dropped.
The ROWID consists of the following three components, the combination of which
uniquely identifies the physical storage location of the row.
Ø Oracle database file number, which contains the block with the rows
Ø Oracle block address, which contains the row
Ø The row within the block (because each block can hold many rows)
The ROWID is used internally in indexes as a quick means of retrieving rows with a
particular key value. Application developers also use it in SQL statements as a quick
way to access a row once they know the ROWID
83. What is Oracle Block? Can two Oracle Blocks have the same address?
Oracle "formats" the database files into a number of Oracle blocks when they are
first created—making it easier for the RDBMS software to manage the files and
easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of
the block size, the entire block is not available for holding data; Oracle takes up
some space to manage the contents of the block. This block header has a minimum
size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size
can improve performance, but it should be done only when the database is first
created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two
blocks can have the same block address if they are in different database files.
84. What is database Trigger?
A database trigger is a PL/SQL block that can defined to automatically execute for
insert, update, and delete statements against a table. The trigger can e defined to
execute once for the entire statement or once for every row that is inserted,
updated, or deleted. For any one table, there are twelve events for which you can
define database triggers. A database trigger can call database procedures that are
also written in PL/SQL.
85. Name two utilities that Oracle provides, which are use for backup and recovery.
Along with the RDBMS software, Oracle provides two utilities that you can use to
back up and restore the database. These utilities are Export and Import.
The Export utility dumps the definitions and data for the specified part of the
database to an operating system binary file. The Import utility reads the file
produced by an export, recreates the definitions of objects, and inserts the data
If Export and Import are used as a means of backing up and recovering the
database, all the changes made to the database cannot be recovered since the
export was performed. The best you can do is recover the database to the time when
the export was last performed.
86. What are stored-procedures? And what are the advantages of using them.
Stored procedures are database objects that perform a user defined operation. A
stored procedure can have a set of compound SQL statements. A stored procedure
executes the SQL commands and returns the result to the client. Stored procedures
are used to reduce network traffic.
87. How are exceptions handled in PL/SQL? Give some of the internal exceptions'
name
PL/SQL exception handling is a mechanism for dealing with run-time errors
encountered during procedure execution. Use of this mechanism enables execution
to continue if the error is not severe enough to cause procedure termination.
The exception handler must be defined within a subprogram specification. Errors
cause the program to raise an exception with a transfer of control to the exceptionhandler
block. After the exception handler executes, control returns to the block in
which the handler was defined. If there are no more executable statements in the
block, control returns to the caller.
User-Defined Exceptions
PL/SQL enables the user to define exception handlers in the declarations area of
subprogram specifications. User accomplishes this by naming an exception as in the
following example:
ot_failure EXCEPTION;
In this case, the exception name is ot_failure. Code associated with this handler is
written in the EXCEPTION specification area as follows:
EXCEPTION
when OT_FAILURE then
out_status_code := g_out_status_code;
out_msg := g_out_msg;
The following is an example of a subprogram exception:
EXCEPTION
when NO_DATA_FOUND then
g_out_status_code := 'FAIL';
RAISE ot_failure;
Within this exception is the RAISE statement that transfers control back to the
ot_failure exception handler. This technique of raising the exception is used to invoke
all user-defined exceptions.
System-Defined Exceptions
Exceptions internal to PL/SQL are raised automatically upon error. NO_DATA_FOUND
is a system-defined exception. Table below gives a complete list of internal
exceptions.
PL/SQL internal exceptions.
PL/SQL internal exceptions.
Exception Name Oracle Error
CURSOR_ALREADY_OPEN ORA-06511
DUP_VAL_ON_INDEX ORA-00001
INVALID_CURSOR ORA-01001
INVALID_NUMBER ORA-01722
LOGIN_DENIED ORA-01017
NO_DATA_FOUND ORA-01403
NOT_LOGGED_ON ORA-01012
PROGRAM_ERROR ORA-06501
STORAGE_ERROR ORA-06500
TIMEOUT_ON_RESOURCE ORA-00051
TOO_MANY_ROWS ORA-01422
TRANSACTION_BACKED_OUT ORA-00061
VALUE_ERROR ORA-06502
ZERO_DIVIDE ORA-01476
In addition to this list of exceptions, there is a catch-all exception named OTHERS
that traps all errors for which specific error handling has not been established.
88. Does PL/SQL support "overloading"? Explain
The concept of overloading in PL/SQL relates to the idea that you can define
procedures and functions with the same name. PL/SQL does not look only at the
referenced name, however, to resolve a procedure or function call. The count and
data types of formal parameters are also considered.
PL/SQL also attempts to resolve any procedure or function calls in locally defined
packages before looking at globally defined packages or internal functions. To further
ensure calling the proper procedure, you can use the dot notation. Prefacing a
procedure or function name with the package name fully qualifies any procedure or
function reference.
89. Tables derived from the ERD
a) Are totally unnormalised
b) Are always in 1NF
c) Can be further denormalised
d) May have multi-valued attributes
90. Spurious tuples may occur due to
i. Bad normalization
ii. Theta joins
iii. Updating tables from join
a) i & ii b) ii & iii
c) i & iii d) ii & iii
(a) i & iii because theta joins are joins made on keys that are not primary keys.
91. A B C is a set of attributes. The functional dependency is as follows
AB -> B
AC -> C
C -> B
a) is in 1NF
b) is in 2NF
c) is in 3NF
d) is in BCNF
(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the primary key. Since C B is a FD
given, where neither C is a Key nor B is a prime attribute, this it is not in 3NF.
Further B is not functionally dependent on key AC thus it is not in 2NF. Thus the
given FDs is in 1NF.
92. In mapping of ERD to DFD
a) entities in ERD should correspond to an existing entity/store in DFD
b) entity in DFD is converted to attributes of an entity in ERD
c) relations in ERD has 1 to 1 correspondence to processes in DFD
d) relationships in ERD has 1 to 1 correspondence to flows in DFD
(a) entities in ERD should correspond to an existing entity/store in DFD
93. A dominant entity is the entity
a) on the N side in a 1 : N relationship
b) on the 1 side in a 1 : N relationship
c) on either side in a 1 : 1 relationship
d) nothing to do with 1 : 1 or 1 : N relationship
(b) on the 1 side in a 1 : N relationship
94. Select 'NORTH', CUSTOMER From CUST_DTLS Where REGION = 'N' Order By
CUSTOMER Union Select 'EAST', CUSTOMER From CUST_DTLS Where REGION = 'E'
Order By CUSTOMER
The above is
a) Not an error
b) Error - the string in single quotes 'NORTH' and 'SOUTH'
c) Error - the string should be in double quotes
d) Error - ORDER BY clause
(d) Error - the ORDER BY clause. Since ORDER BY clause cannot be used in UNIONS
95. What is Storage Manager?
It is a program module that provides the interface between the low-level data stored
in database, application programs and queries submitted to the system.
96. What is Buffer Manager?
It is a program module, which is responsible for fetching data from disk storage into
main memory and deciding what data to be cache in memory.
97. What is Transaction Manager?
It is a program module, which ensures that database, remains in a consistent state
despite system failures and concurrent transaction execution proceeds without
conflicting.
98. What is File Manager?
It is a program module, which manages the allocation of space on disk storage and
data structure used to represent information stored on a disk.
99. What is Authorization and Integrity manager?
It is the program module, which tests for the satisfaction of integrity constraint and
checks the authority of user to access data.
100. What are stand-alone procedures?
Procedures that are not part of a package are known as stand-alone because they
independently defined. A good example of a stand-alone procedure is one written in
a SQL*Forms application. These types of procedures are not available for reference
from other Oracle tools. Another limitation of stand-alone procedures is that they are
compiled at run time, which slows execution.
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