Question 1. What Is Rdbms?
Answer
: Relational Data Base
Management Systems (RDBMS) are database management systems that maintain data
records and indices in tables. Relationships may be created and maintained
across and among the data and tables. In a relational database, relationships
between data items are expressed by means of tables. Interdependencies among
these tables are expressed by data values rather than by pointers. This allows
a high degree of data independence. An RDBMS has the capability to recombine
the data items from different files, providing powerful tools for data usage.
Question
2. What Is Normalization?
Answer
: Database normalization
is a data design and organization process applied to data structures based on
rules that help build relational databases. In relational database design, the
process of organizing data to minimize redundancy. Normalization usually
involves dividing a database into two or more tables and defining relationships
between the tables. The objective is to isolate data so that additions,
deletions, and modifications of a field can be made in just one table and then
propagated through the rest of the database via the defined relationships.
Question
3. What Are Different Normalization Forms?
Answer
:
1NF: Eliminate Repeating Groups Make a separate table for each set of
related attributes, and give each table a primary key. Each field contains at
most one value from its attribute domain.
2NF: Eliminate Redundant Data If an attribute depends on only
part of a multi-valued key, remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key If attributes do not
contribute to a description of the key, remove them to a separate table. All
attributes must be directly dependent on the primary key.
BCNF: Boyce-Codd Normal Form If there are non-trivial dependencies
between candidate key attributes, separate them out into distinct tables.
4NF: Isolate Independent Multiple Relationships No table may
contain two or more 1:n or n:m relationships that are not directly related.
5NF: Isolate Semantically Related Multiple Relationships There may be
practical constrains on information that justify separating logically related
many-to-many relationships.
ONF: Optimal Normal Form A model limited to only simple
(elemental) facts, as expressed in Object Role Model notation.
DKNF: Domain-Key Normal Form A model free from all modification
anomalies. Remember, these normalization guidelines are cumulative. For a
database to be in 3NF, it must first fulfill all the criteria of a 2NF and 1NF
database.
Question
4. What Is Stored Procedure?
Answer
: A stored procedure is a
named group of SQL statements that have been previously created and stored in
the server database. Stored procedures accept input parameters so that a single
procedure can be used over the network by several clients using different input
data. And when the procedure is modified, all clients automatically get the new
version. Stored procedures reduce network traffic and improve performance.
Stored procedures can be used to help ensure the integrity of the database.
e.g.
sp_helpdb, sp_renamedb, sp_depends etc.
Question
5. What Is Trigger?
Answer
: A trigger is a SQL
procedure that initiates an action when an event (INSERT, DELETE or UPDATE)
occurs. Triggers are stored in and managed by the DBMS. Triggers are used to
maintain the referential integrity of data by changing the data in a systematic
fashion. A trigger cannot be called or executed; the DBMS automatically fires
the trigger as a result of a data modification to the associated table.
Triggers can be viewed as similar to stored procedures in that both consist of
procedural logic that is stored at the database level. Stored procedures,
however, are not event-drive and are not attached to a specific table as
triggers are. Stored procedures are explicitly executed by invoking a CALL to
the procedure while triggers are implicitly executed. In addition, triggers can
also execute stored procedures.
Question
6. What Is View?
Answer
: A simple view can be
thought of as a subset of a table. It can be used for retrieving data, as well
as updating or deleting rows. Rows updated or deleted in the view are updated
or deleted in the table the view was created with. It should also be noted that
as data in the original table changes, so does data in the view, as views are
the way to look at part of the original table. The results of using a view are
not permanently stored in the database. The data accessed through a view is
actually constructed using standard T-SQL select command and can come from one
to many different base tables or even other views.
Question
7. What Is Index?
Answer
: An index is a physical
structure containing pointers to the data. Indices are created in an existing
table to locate rows more quickly and efficiently. It is possible to create an
index on one or more columns of a table, and each index is given a name. The
users cannot see the indexes, they are just used to speed up queries. Effective
indexes are one of the best ways to improve performance in a database
application. A table scan happens when there is no index available to help a
query. In a table scan SQL Server examines every row in the table to satisfy
the query results. Table scans are sometimes unavoidable, but on large tables,
scans have a terrific impact on performance. Clustered indexes define the
physical sorting of a database table’s rows in the storage media. For this
reason, each database table may have only one clustered index. Non-clustered
indexes are created outside of the database table and contain a sorted list of
references to the table itself.
Question
8. What Is Database?
Answer
: 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.
Question
9. What Is Dbms?
Answer
: 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.
Question
10. What Is A Database System?
Answer
: The database and DBMS
software together is called as Database system.
Question
11. Advantages Of Dbms?
Answer
:
Redundancy
is controlled.
Unauthorised
access is restricted.
Providing
multiple user interfaces.
Enforcing
integrity constraints.
Providing
backup and recovery.
Question
12. Disadvantage In File Processing System?
Answer
:
Data
redundancy & inconsistency.
Difficult
in accessing data.
Data
isolation.
Data
integrity.
Concurrent
access is not possible.
Security
Problems.
Question
13. Describe The Three Levels Of Data Abstraction?
Answer
:There are three levels of
abstraction:
Physical
level: The lowest level of abstraction describes how data are
stored.
Logical level: The next higher level of abstraction, describes what data
are stored in database and what relationship among those data.
View
level: The highest level of abstraction describes only part of
entire database.
Question
14. Define The "integrity Rules"?
Answer
:There are two Integrity
rules.
Entity
Integrity: States that “Primary key cannot have NULL value”.
Referential
Integrity: States that “Foreign Key can be either a NULL value or should be
Primary Key value of other relation.
Question
15. What Is Extension And Intension?
Answer
:
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.
Question
16. What Is System R? What Are Its Two Major Subsystems?
Answer
: 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
Research
Storage
System
Relational Data System.
Question
17. How Is The Data Structure Of System R Different From The Relational
Structure?
Answer
:Unlike Relational
systems in System R
Domains
are not supported
Enforcement
of candidate key uniqueness is optional
Enforcement
of entity integrity is optional
Referential
integrity is not enforced
Question
18. What Is Data Independence?
Answer
: 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:
Physical
Data Independence: Modification in physical level should not affect the logical
level.
Logical
Data Independence: Modification in logical level should affect the view level.
Question
19. What Is A View? How It Is Related To Data Independence?
Answer
: 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.
Question
20. What Is Data Model?
Answer
: A collection of
conceptual tools for describing data, data relationships data semantics and
constraints.
Question
21. What Is E-r Model?
Answer
: 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.
Question
22. What Is Object Oriented Model?
Answer
: This model is based on
collection of objects. An object contains values stored in instance variables
with in 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.
Question
23. What Is An Entity?
Answer
: It is a 'thing' in the
real world with an independent existence.
Question
24. What Is An Entity Type?
Answer
: It is a collection (set)
of entities that have same attributes.
Question
25. What Is An Entity Set?
Answer
: It is a collection of
all entities of particular entity type in the database.
Question
26. What Is An Extension Of Entity Type?
Answer
: The collections of
entities of a particular entity type are grouped together into an entity set.
Question
27. What Is Weak Entity Set?
Answer
: 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.
Question
28. What Is An Attribute?
Answer
:It is a particular
property, which describes the entity.
Question
29. What Is A Relation Schema And A Relation?
Answer
: 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).
Question
30. What Is Degree Of A Relation?
Answer
: It is the number of
attribute of its relation schema.
Question
31. What Is Relationship?
Answer
: It is an association
among two or more entities.
Question
32. What Is Relationship Set?
Answer
: The collection (or set)
of similar relationships.
Question
33. What Is Relationship Type?
Answer
: Relationship type
defines a set of associations or a relationship set among a given set of entity
types.
Question
34. What Is Degree Of Relationship Type?
Answer
: It is the number of
entity type participating.
Question
35. What Is Ddl (data Definition Language)?
Answer
: A data base schema is
specifies by a set of definitions expressed by a special language called DDL.
Question
36. What Is Vdl (view Definition Language)?
Answer
: It specifies user views
and their mappings to the conceptual schema.
Question
37. What Is Sdl (storage Definition Language)?
Answer
: This language is to
specify the internal schema. This language may specify the mapping between two
schemas.
Question
38. What Is Data Storage - Definition Language?
Answer
: 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.
Question
39. What Is Dml (data Manipulation Language)?
Answer
: This language that
enable user to access or manipulate data as organized by appropriate data
model.
Procedural
DML or Low level: DML requires a user to specify what data are needed and how
to get those data.
Non-Procedural
DML or High level: DML requires a user to specify what data are needed
without specifying how to get those data.
Question
40. What Is Dml Compiler?
Answer
: It translates DML
statements in a query language into low-level instruction that the query
evaluation engine can understand.
Question
41. What Is Query Evaluation Engine?
Answer
: It executes low-level
instruction generated by compiler.
Question
42. What Is Ddl Interpreter?
Answer
: It interprets DDL
statements and record them in tables containing metadata.
Question
43. What Is Record-at-a-time?
Answer
: 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.
Question
44. What Is Set-at-a-time Or Set-oriented?
Answer
: 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.
Question
45. What Is Relational Algebra?
Answer
: 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.
Question
46. What Is Relational Calculus?
Answer : 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.
Question
47. How Does Tuple-oriented Relational Calculus Differ From Domain-oriented
Relational Calculus?
Answer
: 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.
Question
48. What Is Functional Dependency?
Answer
: 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.
Question
49. When Is A Functional Dependency F Said To Be Minimal?
Answer
:
Every
dependency in F has a single attribute for its right hand side.
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 remove any dependency from F and still have set of dependency that is
equivalent to F.
Question
50. What Is Multivalued Dependency?
Answer
: 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
t3[x]
= t4[X] = t1[X] = t2[X]
t3[Y]
= t1[Y] and t4[Y] = t2[Y]
t3[Z]
= t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
Question
51. What Is Lossless Join Property?
Answer
: It guarantees that the
spurious tuple generation does not occur with respect to relation schemas after
decomposition.
Question
52. What Is 1 Nf (normal Form)?
Answer
: The domain of attribute
must include only atomic (simple, indivisible) values.
Question
53. What Is Fully Functional Dependency?
Answer
: 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.
Question
54. What Is 2nf?
Answer
: 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.
Question
55. What Is 3nf?
Answer
: A relation schema R is
in 3NF if it is in 2NF and for every FD X A either of the following is true
X
is a Super-key of R.
A
is a prime attribute of R.
In other words, if every
non prime attribute is non-transitively dependent on primary key.
Question
56. What Is Bcnf (boyce-codd Normal Form)?
Answer
: 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.
Question
57. What Is 4nf?
Answer
: 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
X
is subset or equal to (or) XY = R.
X
is a super key.
Question
58. What Is 5nf?
Answer
: 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
Ri
= R for some i.
The
join dependency is implied by the set of FD, over R in which the left side is
key of R.
Question
59. What Is Domain-key Normal Form?
Answer
: A relation is said to be
in DKNF if all constraints and dependencies that should hold on the constraint
can be enforced by simply enforcing the domain constraint and key constraint on
the relation.
Question
60. What Are Partial, Alternate, Artificial, Compound And Natural Key?
Answer
:
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.
Question
61. What Is Indexing And What Are The Different Kinds Of Indexing?
Answer:
Indexing is a technique
for determining how quickly specific data can be found.
Types:
Binary
search style indexing
B-Tree
indexing
Inverted
list indexing
Memory
resident table
Table
indexing
Question
62. What Is System Catalog Or Catalog Relation? How Is Better Known As?
Answer
: 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.
Question
63. What Is Meant By Query Optimization?
Answer
: The phase that
identifies an efficient execution plan for evaluating a query that has the
least estimated cost is referred to as query optimization.
Question
64. What Is Join Dependency And Inclusion Dependency?
Answer
:
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.
Question
65. What Is Durability In Dbms?
Answer
: 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.
Question
66. What Do You Mean By Atomicity And Aggregation?
Answer
:
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.
Question
67. What Is A Phantom Deadlock?
Answer
: 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.
Question
68. What Is A Checkpoint And When Does It Occur?
Answer
: 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.
Question
69. What Are The Different Phases Of Transaction?
Answer
: Different phases are
Analysis
phase
Redo
Phase
Undo
phase
Question
70. What Do You Mean By Flat File Database?
Answer
: 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.
Question
71. What Is "transparent Dbms"?
Answer
: It is one, which keeps
its Physical Structure hidden from user.
Question
72. Brief Theory Of Network, Hierarchical Schemas And Their Properties?
Answer
: 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.
Question
73. What Is A Query?
Answer
: 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.
Question
74. What Do You Mean By Correlated Subquery?
Answer
: 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)
Question
75. What Are The Primitive Operations Common To All Record Management Systems?
Answer
: Addition, deletion and
modification.
Question
76. Name The Buffer In Which All The Commands That Are Typed In Are Stored?
Answer
: ‘Edit’ Buffer.
Question
77. What Are The Unary Operations In Relational Algebra?
Answer
: PROJECTION and
SELECTION.
Question
78. Are The Resulting Relations Of Product And Join Operation The Same?
Answer
: 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.
Question
79. What Is Rdbms Kernel?
Answer
: 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.
Question
80. Name The Sub-systems Of A Rdbms?
Answer
: I/O, Security, Language
Processing, Process Control, Storage Management, Logging and Recovery,
Distribution Control, Transaction Control, Memory Management, Lock Management.
Question
81. Which Part Of The Rdbms Takes Care Of The Data Dictionary? How
Answer
: 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.
Question
82. What Is The Job Of The Information Stored In Data-dictionary?
Answer
: The information in the
data dictionary validates the existence of the objects, provides access to
them, and maps the actual physical storage location.
Question
83. Not Only Rdbms Takes Care Of Locating Data It Also?
Answer
: determines an optimal
access path to store or retrieve the data.
Question
84. How Do You Communicate With An Rdbms?
Answer
: You communicate with an
RDBMS using Structured Query Language (SQL).
Question
85. Define Sql And State The Differences Between Sql And Other Conventional
Programming Languages?
Answer
: 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.
Question
86. Name The Three Major Set Of Files On Disk That Compose A Database In
Oracle?
Answer
: There are three major
sets of files on disk that compose a database. All the files are binary. These
are
Database
files
Control
files
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.
Question
87. What Is An Oracle Instance?
Answer
: 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.
Question
88. What Are The Four Oracle System Processes That Must Always Be Up And
Running For The Database To Be Useable
Answer
: 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).
Question
89. What Is Rowid?
Answer
: 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.
·
Oracle database file number, which contains the block with the
rows
·
Oracle block address, which contains the row
·
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.
Question
90. What Is Oracle Block? Can Two Oracle Blocks Have The Same Address?
Answer
: 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.
Question
91. What Is Database Trigger?
Answer
: 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 be 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.
Question
92. Name Two Utilities That Oracle Provides, Which Are Use For Backup And
Recovery.
Answer
: 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.
Question
93. What Are Stored-procedures? And What Are The Advantages Of Using Them.
Answer
: 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.
Question
94. Does Pl/sql Support "overloading"? Explain
Answer
: 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.
Question
95. What Is Storage Manager?
Answer
: 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.
Question
96. What Is Buffer Manager?
Answer
: 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.
Question
97. What Is Transaction Manager?
Answer
: It is a program module,
which ensures that database, remains in a consistent state despite system
failures and concurrent transaction execution proceeds without conflicting.
Question
98. What Is File Manager?
Answer
: 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.
Question
99. What Is Authorization And Integrity Manager?
Answer
: It is the program
module, which tests for the satisfaction of integrity constraint and checks the
authority of user to access data.
Question
100. What Are Stand-alone Procedures?
Answer
: 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.
Question
101. What Are Cursors Give Different Types Of Cursors.
Answer
: PL/SQL uses cursors for
all database information accesses statements. The language supports the use two
types of cursors.
Implicit
Explicit
Question
102. What Is Meant By Proactive, Retroactive And Simultaneous Update?
Answer
:
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.
Simultaneous Update: The updates that are applied to database at the
same time when it becomes effective in real world.