Database Reference
In-Depth Information
5.1.1 Database Model
The database model is the blueprint for the database design. Database modeling is
therefore the preparation of that blueprint. In database modeling, we construct a
representation of the database that will be useful towards the design and construction of
the database. Various approaches to database modeling have been proposed by different
authors; the prominent ones are:
•
The Entity-Relationship (E-R) Model
•
The Object-Relationship (O-R) Model
•
The Extended Relational Model
The E-R and O-R models were introduced in chapter 3 (sections 3.5.1 and 3.5.2).
Chapter 3 also introduced the Relation-Attributes List (RAL) and the Relationship List
(RL section 3.6) as an alternative to the E-R model in situations where E-R modeling is
impractical. We will revisit the E-R model later in this chapter, and then introduce the
extended relational model.
5.1.2 Database Design
The database design is the (final) specification that will be used to construct the actual
database. Database designing is therefore the preparation of this specification. In
preparing the database specification, the database model is used as input. As such, the
guidelines given in chapter 3 (section 3.5.4) on implementing relationships are applicable.
Five approaches to database design that will be discussed later in this chapter are:
•
Database Design via the E-R Model
•
Database Design via the Extended Relational Model
•
Database Design via the UML Model
•
Database Design via the Entity/Object Specification Grid
•
Database Design via Normalization Theory
5.2 The E-R Model Revisited
Recall that in chapter 3, the similarity and differences between an entity and a relation
were noted. If we assume the similarity, then the E-R model can be construed as merely a
specific interpretation of the relational model.
