Technical Note on DBMS

DBMS Notes:
By: Vedanand Singh
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?
1. Redundancy is controlled.
2. Unauthorised access is restricted.
3. Providing multiple user interfaces.
4. Enforcing integrity constraints.
5. Providing backup and recovery.
5. What are the disadvantage in File Processing
System?
1. Data redundancy and inconsistency.
2. Difficult in accessing data.
3. Data isolation.
4. Data integrity.
5. Concurrent access is not possible.

6. Security Problems.
6. Describe the three levels of data abstraction?
The are three levels of abstraction:
1. Physical level: The lowest level of abstraction
describes how data are stored.
2. Logical level: The next higher level of abstraction,
describes what data are stored in database and what
relationship among those data.
3. View level: The highest level of abstraction describes
only part of entire database.
7. Define the "integrity rules"?
There are two Integrity rules.
1. Entity Integrity: States that "Primary key cannot
have NULL value"
2. 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?
1. Extension: It is the number of tuples present in a
table at any instance. This is time dependent.
2. 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
1. Research Storage
2. System Relational Data System.
10. How is the data structure of System R different
from the relational structure?
Unlike Relational systems in System R
1. Domains are not supported
2. Enforcement of candidate key uniqueness is optional
3. Enforcement of entity integrity is optional
4. 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:
1. Physical Data Independence: Modification in
physical level should not affect the logical level.
2. 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 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.
1. Procedural DML or Low level: DML requires a user
to specify what data are needed and how to get those
data.
2. 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?

1. The tuple-oriented calculus uses a tuple variables
i.e., variable whose only permitted values are tuples
of that relation. E.g. QUEL
2. 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
1. X is a Super-key of R.
2. 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?
1. 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.
2. Alternate Key: All Candidate Keys excluding the
Primary Key are known as Alternate Keys.
3. 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.
4. 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.
5. 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:
1. Binary search style indexing
2. B-Tree indexing
3. Inverted list indexing

4. Memory resident table
5. 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?
1. 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.
2. 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 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.
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 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
85. What is cold backup and hot backup (in case of
Oracle)?
1. 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.
2. 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.
1. Proactive Update: The updates that are applied to
database before it becomes effective in real world.
2. Retroactive Update: The updates that are applied to
database after it becomes effective in real world.
3. Simulatneous Update: The updates that are applied
to database at the same time when it becomes
effective in real world.

Technical Note on DBMS

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Technical Note on DBMS