1. What is database?
A database is a logically coherent
collection of data with some inherent meaning, representing some aspect ofreal 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.
3. What is a Database system?
The database and DBMS software
together is called as Database system.
4. What are the advantages
of DBMS?
Redundancy is controlled.
Unauthorised access is
restricted.
Providing multiple user interfaces.
Enforcing integrity constraints.
Providing backup and recovery.
5. What are the
disadvantage in File Processing System?
Data redundancy and inconsistency.
Difficult in accessing data.
Data isolation.
Data integrity.
Concurrent access is not possible.
Security Problems.
6. Describe the three
levels of data abstraction?
The 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.
7. Define the "integrity rules"?
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.
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
Its two subsystems are
Research
Storage
System
Relational Data System.
10. How is the data structure of System R different from the
relational structure?
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
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:
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.
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.
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 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.
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.
28. What is DDL (Data Definition Language)?
A
data base schema is specifies by
a set of definitions expressed by a special language called DDL.
29. What is VDL (View Definition Language)?
It
specifies user views and their mappings to the conceptual schema.
30. What is SDL (Storage Definition Language)?
This
language is to specify the internal schema. This language may specify the mapping between two
schemas.
31. 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.
32. What is DML (Data Manipulation Language)?
This
language that enable user to access or manipulate data as organised 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.
33. What is DML Compiler?
It
translates DML statements in a query language into low-level
instruction that the query evaluation engine can understand.
34. What is Query evaluation engine?
It
executes low-level instruction generated by compiler.
35. What is DDL Interpreter?
It
interprets DDL statements and record them in tables containing metadata.
36. 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.
37. 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.
38. 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.
39. 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.
40. 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
underlyingdomains instead of over relation. E.g. ILL, DEDUCE.
41. 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
(1).Minimizing redundancy, (2). Minimizing insertion, deletion and update anomalies.
(1).Minimizing redundancy, (2). Minimizing insertion, deletion and update anomalies.
42. 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.
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 onprimary 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
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.
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.
1.) X is subset or equal to (or) XY = R.
2.) X is a super key.
1.) X is subset or equal to (or) XY = R.
2.) 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 1.) Ri = R for some i.
2.) The join dependency is implied by the set of FD, over R in which the left side is key of R.
2.) 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:
Binary search style indexing
B-Tree
indexing
Inverted
list indexing
Memory
resident table
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 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.
57. 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.
58. 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.
59. 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.
60. What are the different phases of transaction?
Different
phases are
1.) Analysis phase,
2.) Redo Phase,
3.) Undo phase.
1.) Analysis phase,
2.) Redo Phase,
3.) Undo phase.
61. 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.
62. What is "transparent DBMS"?
It
is one, which keeps its Physical Structure hidden from user.
63. 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.
64. 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.
Example: Select
* From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM =
ORDER.CNUM)
65. What are the primitive operations common to all record management systems?
Addition,
deletion and modification.
66. Name the buffer in which all the commands that are typed in
are stored?
'Edit'
Buffer.
67. What are the unary operations in Relational Algebra?
PROJECTION
and SELECTION.
68. 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.
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.
69. 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.
70. 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.
71. 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.
72. 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.
73. How do you communicate with an RDBMS?
You
communicate with an RDBMS using Structured Query Language (SQL).
74. 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 normalizedrelational 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.
75. 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
1.)
Database files
2.) Control files
3.) Redo logs
2.) Control files
3.) 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.
76. 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.
77. 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.
78. 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.
79. 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.
80. 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.
81. 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.
82. 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.
83. 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.
84. 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
1.) Implicit
2.) Explicit
1.) Implicit
2.) Explicit
85. What is cold backup and hot backup (in case of
Oracle)?
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.
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.
86. 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.
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