Page 243 - DCAP405_SOFTWARE_ENGINEERING

Software Engineering

Notes 14.1 Data Models

To design any system, we require a mathematical model. Similarly, for DB Systems there are
several models being used as given below:

Hierarchical Model
Network Model

Relational Model
Object-relational Model
Object Model
Out of all the above models, the Relational Model is used by most of the database management
packages, including Oracle, Ingres, Sybase, etc.
Hierarchical, Network, and Relational Models

Data pertaining to the real world applications are not isolated entities rather they are related to
each other in many ways – simple and complex. A data model captures the essence of relation
with the data items. Various data models view data and their relationships in different ways. In
the following section we discuss the first two conventional data models – Hierarchical and
Network – in reverse order.
Relational Model

The model was first introduced by Tod Codd of IBM Research in 1970. It uses the concept of a
mathematical relation. Hence, the database is considered as a collection of relations. A relation
can be thought as a table of values, each row in the table represents a collection of related data
values. In relational model terminology, a row in the table is called a tuple and a column header
is called an attribute.
A relation schema R, denoted by R(A ,...,A ) , is made up of a relation name R and a list of
1 n
attributes A ,...,A . The domain of A , denoted by dom(A ) is the set of all the possible values this
1 n i i
attribute may take.
A relation schema that describes a relation R is called the name of this relation. The degree of a
relation is the number of attributes in its relation schema.

!
Caution A record contains information regarding a single person or thing of interest.

A field stores data regarding a particular aspect of that person or thing. The organization is
illustrated below:

236 LOVELY PROFESSIONAL UNIVERSITY