DBMS Basics
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
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 disadvantages 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?
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.
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
- 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:
- 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 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 are 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)?
The 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 underlying domains 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
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 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
- 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
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.
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:
Types:
- Binary search style indexing
- B-Tree indexing
- Inverted list indexing
- Memory resident table
- Table indexing
54. What is
system catalogue or catalogue 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
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 sub query?
Sub queries, or nested queries, are used to bring
back a set of rows to be used by the parent query. Depending on how the sub
query 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 sub query is
executed for each row of the parent, this is called a correlated sub query.
A correlated sub query can be easily identified if
it contains any references to the parent sub query columns in its WHERE clause.
Columns from the sub query cannot be referenced anywhere else in the parent
query. The following example demonstrates a non-correlated sub query.
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 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.
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
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 the entire 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
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.
- Simultaneous Update: The updates that are applied to database at
the same time when it becomes effective in real world.
Really nice hardwork thanks for sharing such helpful questions
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