RDBMS Interview Questions and Answers
1.
What is database?
A database is a logically coherent collection of data
with some inherent meaning, representing some aspect of real world and which is
designed, built and populated with data for a specific purpose.
2.
What is DBMS?
It is a collection of programs that
enables user to create and maintain a database. In other words it is
general-purpose software that provides the users with the processes of defining,
constructing and manipulating the database for various applications.
The database and DBMS software
together is called as Database system.
4.
Advantages of DBMS?
Ø
Redundancy
is controlled.
Ø
Unauthorised
access is restricted.
Ø
Providing
multiple user interfaces.
Ø
Enforcing
integrity constraints.
Ø
Providing
backup and recovery.
5.
Disadvantage in File Processing
System?
Ø
Data
redundancy & inconsistency.
Ø
Difficult
in accessing data.
Ø
Data
isolation.
Ø
Data
integrity.
Ø
Concurrent
access is not possible.
Ø
Security
Problems.
6.
Describe the three levels of data
abstraction?
The are three levels of abstraction:
Ø
Physical
level: The lowest level of abstraction describes how data are stored.
Ø
Logical
level: The next higher level of abstraction, describes what data are stored in
database and what relationship among those data.
Ø
View
level: The highest level of abstraction describes only part of entire database.
7. Define the "integrity
rules"?
There
are two Integrity rules.
Ø Entity
Integrity: States that “Primary key
cannot have NULL value”
Ø Referential
Integrity: States that “Foreign Key
can be either a NULL value or should be Primary Key value of other relation.
8. What is extension and intension?
Extension -
It
is the number of tuples present in a table at any instance. This is time
dependent.
Intension -
It
is a constant value that gives the name, structure of table and the constraints
laid on it.
9. What is System R? What are its two
major subsystems?
System
R was designed and developed over a period of 1974-79 at IBM San Jose Research
Center. It is a prototype and its purpose was to demonstrate that it is
possible to build a Relational System that can be used in a real life
environment to solve real life problems, with performance at least comparable
to that of existing system.
Its two subsystems are
Ø Research
Storage
Ø System
Relational Data System.
10. How is the data structure of System
R different from the relational structure?
Unlike
Relational systems in System R
Ø Domains
are not supported
Ø Enforcement
of candidate key uniqueness is optional
Ø Enforcement
of entity integrity is optional
Ø Referential
integrity is not enforced
11.
What is Data Independence?
Data
independence means that “the application is independent of the storage
structure and access strategy of data”. In other words, The ability to modify
the schema definition in one level should not affect the schema definition in
the next higher level.
Two types of Data Independence:
Ø
Physical
Data Independence: Modification in physical level should not affect the logical
level.
Ø
Logical
Data Independence: Modification in logical level should affect the view level.
NOTE:
Logical Data Independence is more difficult to achieve
12. What is a view? How it is related to
data independence?
A
view may be thought of as a virtual table, that is, a table that does not
really exist in its own right but is instead derived from one or more
underlying base table. In other words, there is no stored file that direct
represents the view instead a definition of view is stored in data dictionary.
Growth
and restructuring of base tables is not reflected in views. Thus the view can
insulate users from the effects of restructuring and growth in the database.
Hence accounts for logical data independence.
13.
What is Data Model?
A collection of conceptual tools for
describing data, data relationships data semantics and constraints.
14.
What is E-R model?
This data model is based on real
world that consists of basic objects called entities and of relationship among
these objects. Entities are described in a database by a set of attributes.
15.
What is Object Oriented model?
This model is based on collection of
objects. An object contains values stored in instance variables within the object.
An object also contains bodies of code that operate on the object. These bodies
of code are called methods. Objects that contain same types of values and the
same methods are grouped together into classes.
16.
What is an Entity?
It is a 'thing' in the real world
with an independent existence.
17.
What is an Entity type?
It is a collection (set) of entities
that have same attributes.
18.
What is an Entity set?
It is a collection of all entities
of particular entity type in the database.
19.
What is an Extension of entity type?
The collections of entities of a
particular entity type are grouped together into an entity set.
20.
What is Weak Entity set?
An entity set may not have
sufficient attributes to form a primary key, and its primary key compromises of
its partial key and primary key of its parent entity, then it is said to be
Weak Entity set.
21.
What is an attribute?
It is a particular property, which
describes the entity.
22.
What is a Relation Schema and a
Relation?
A relation Schema denoted by R(A1,
A2, …, An) is made up of the relation name R and the list of attributes Ai that
it contains. A relation is defined as a set of tuples. Let r be the relation
which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list
of n-values t=(v1,v2, ..., vn).
23.
What is degree of a Relation?
It is the number of attribute of its
relation schema.
24.
What is Relationship?
It is an association among two or
more entities.
25.
What is Relationship set?
The collection (or set) of similar
relationships.
26.
What is Relationship type?
Relationship type defines a set of
associations or a relationship set among
a given set of entity types.
27.
What is degree of Relationship type?
It is the number of entity type
participating.
25.
What is DDL (Data Definition
Language)?
A data base schema is specifies by a
set of definitions expressed by a special language called DDL.
26.
What is VDL (View Definition
Language)?
It specifies user views and their
mappings to the conceptual schema.
27.
What is SDL (Storage Definition
Language)?
This language is to specify the
internal schema. This language may specify the mapping between two schemas.
28.
What is Data Storage - Definition
Language?
The storage structures and access
methods used by database system are specified by a set of definition in a
special type of DDL called data storage-definition language.
29.
What is DML (Data Manipulation
Language)?
This language that enable user to
access or manipulate data as organized by appropriate data model.
Ø
Procedural
DML or Low level: DML requires a user to specify what data are needed and how
to get those data.
Ø
Non-Procedural
DML or High level: DML requires a user
to specify what data are needed without specifying how to get those data.
30.What is DML
Compiler?
It translates DML statements in a
query language into low-level instruction that the query evaluation engine can
understand.
31.
What is Query evaluation engine?
It executes low-level instruction generated
by compiler.
32.
What is DDL Interpreter?
It interprets DDL statements and
record them in tables containing metadata.
34.
What is Record-at-a-time?
The Low level or Procedural DML can
specify and retrieve each record from a set of records. This retrieve of a
record is said to be Record-at-a-time.
35.
What is Set-at-a-time or
Set-oriented?
The High level or Non-procedural DML
can specify and retrieve many records in a single DML statement. This retrieve
of a record is said to be Set-at-a-time or Set-oriented.
36.
What is Relational Algebra?
It is procedural query language. It
consists of a set of operations that take one or two relations as input and
produce a new relation.
37. What is Relational Calculus?
It
is an applied predicate calculus specifically tailored for relational databases
proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.
38. How does Tuple-oriented relational
calculus differ from domain-oriented relational calculus
The
tuple-oriented calculus uses a tuple variables i.e., variable whose only
permitted values are tuples of that relation. E.g. QUEL
The
domain-oriented calculus has domain variables i.e., variables that range over
the underlying domains instead of over relation. E.g. ILL, DEDUCE.
39. What is normalization?
It is a process of analysing the
given relation schemas based on their Functional Dependencies (FDs) and primary
key to achieve the properties
Ø
Minimizing
redundancy
Ø
Minimizing
insertion, deletion and update anomalies.
40.
What is Functional Dependency?
A
Functional dependency is denoted by X
Y between two sets of attributes X and Y that are subsets of R specifies
a constraint on the possible tuple that can form a relation state r of R. The
constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have
t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely
determines the value of component Y.
41.
When is a functional dependency F
said to be minimal?
Ø
Every
dependency in F has a single attribute for its right hand side.
Ø
We
cannot replace any dependency X A in F
with a dependency Y A where Y is a
proper subset of X and still have a set of dependency that is equivalent to F.
We
cannot replace any dependency X A in F
with a dependency Y A where Y is a
proper subset of X and still have a set of dependency that is equivalent to F.
Ø
We
cannot remove any dependency from F and still have set of dependency that is
equivalent to F.
42.
What is Multivalued dependency?
Multivalued
dependency denoted by X Y
specified on relation schema R, where X and Y are both subsets of R, specifies
the following constraint on any relation r of R: if two tuples t1 and t2 exist
in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the
following properties
Ø
t3[x]
= t4[X] = t1[X] = t2[X]
Ø t3[Y] =
t1[Y] and t4[Y] = t2[Y]
Ø
t3[Z]
= t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
43.
What is Lossless join property?
It guarantees that the spurious
tuple generation does not occur with respect to relation schemas after
decomposition.
44.
What is 1 NF (Normal Form)?
The domain of attribute must include
only atomic (simple, indivisible) values.
45.
What is Fully Functional dependency?
It
is based on concept of full functional dependency. A functional dependency X
Y is full functional dependency if removal of any attribute A from X
means that the dependency does not hold any more.
46.
What is 2NF?
A relation schema R is in 2NF if it
is in 1NF and every non-prime attribute A in R is fully functionally dependent
on primary key.
47.
What is 3NF?
A
relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
Ø
X
is a Super-key of R.
Ø
A
is a prime attribute of R.
In other words, if every non prime
attribute is non-transitively dependent on primary key.
48.
What is BCNF (Boyce-Codd Normal
Form)?
A relation schema R is in BCNF if it is
in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.
49.
What is 4NF?
A
relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following
is true
Ø
X
is subset or equal to (or) XY = R.
Ø
X
is a super key.
50.
What is 5NF?
A Relation schema R is said to be
5NF if for every join dependency {R1,
R2, ..., Rn} that holds R, one the following is true
Ø
Ri
= R for some i.
Ø
The
join dependency is implied by the set of FD, over R in which the left side is
key of R.
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
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 files 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 exception-handler 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.
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
(b) Are always in 1NF
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.
101. What are cursors give different
types of cursors.
PL/SQL uses cursors for all database
information accesses statements. The language supports the use two types of
cursors
Ø
Implicit
Ø
Explicit
102. What is cold backup and hot backup
(in case of Oracle)?
Ø
Cold Backup:
It is copying the three sets of
files (database files, redo logs, and control file) when the instance is shut
down. This is a straight file copy, usually from the disk directly to tape. You
must shut down the instance to guarantee a consistent copy.
If a cold backup is performed, the
only option available in the event of data file loss is restoring all the files
from the latest backup. All work performed on the database since the last
backup is lost.
Ø
Hot Backup:
Some sites (such as worldwide
airline reservations systems) cannot shut down the database while making a
backup copy of the files. The cold backup is not an available option.
So different means of backing up
database must be used — the hot backup. Issue a SQL command to indicate to
Oracle, on a tablespace-by-tablespace basis, that the files of the tablespace
are to backed up. The users can continue to make full use of the files,
including making changes to the data. Once the user has indicated that he/she
wants to back up the tablespace files, he/she can use the operating system to
copy those files to the desired backup destination.
The database must be running in
ARCHIVELOG mode for the hot backup option.
If a data loss failure does occur,
the lost database files can be restored using the hot backup and the online and
offline redo logs created since the backup was done. The database is restored
to the most consistent state without any loss of committed transactions.
103. What are Armstrong rules? How do we
say that they are complete and/or sound
The well-known inference rules for
FDs
Ø
Reflexive
rule :
If Y is subset or equal to X then X Y.
Ø
Augmentation
rule:
If X Y then XZ YZ.
Ø
Transitive
rule:
If {X Y, Y
Z} then X Z.
Ø
Decomposition
rule :
If
X
YZ then X Y.
Ø
Union
or Additive rule:
If {X Y, X Z} then X YZ.
Ø
Pseudo
Transitive rule :
If {X Y, WY Z}
then WX Z.
Of these the first three are known as
Amstrong Rules. They are sound because it is enough if a set of FDs satisfy
these three. They are called complete because using these three rules we can
generate the rest all inference rules.
104. How can you find the minimal key of
relational schema?
Minimal
key is one which can identify each tuple of the given relation schema uniquely.
For finding the minimal key it is required to find the closure that is the set
of all attributes that are dependent on any given set of attributes under the
given set of functional dependency.
Algo. I Determining
X+, closure for X, given set of FDs F
1.
Set X+ = X
2.
Set Old X+ = X+
3.
For each FD Y
Z in F and if Y belongs to X+
then add Z to X+
For each FD Y
Z in F and if Y belongs to X+
then add Z to X+
4.
Repeat steps 2 and 3 until Old X+
= X+
Algo.II Determining
minimal K for relation schema R, given set of FDs F
1.
Set K to R that is make K a set of
all attributes in R
2.
For each attribute A in K
a.
Compute (K – A)+ with
respect to F
b.
If
(K – A)+ = R then set K = (K – A)+
105. What do you understand by dependency
preservation?
Given
a relation R and a set of FDs F, dependency preservation states that the
closure of the union of the projection
of F on each decomposed relation Ri is equal to the closure of F. i.e.,
((PR1(F)) U … U (PRn(F)))+
= F+
if decomposition
is not dependency preserving, then some dependency is lost in the
decomposition.
106. What is meant by Proactive,
Retroactive and Simultaneous Update.
Proactive Update:
The updates that are applied to database
before it becomes effective in real world .
Retroactive Update:
The updates that are applied to database
after it becomes effective in real world .
Simulatneous Update:
The updates that are applied to database
at the same time when it becomes effective in real world .
107.
What are the different types of JOIN
operations?
Equi Join: This is the most common type of join which
involves only equality comparisions. The disadvantage in this type of join is
that there
