Page 96 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Unit 6: Relational Language and Database Design

Notes
Example: We could say < 10 to retrieve sailors with a rating less than 10 or say ¬10 to
retrieve sailors whose rating is not equal to 10. The expression ¬10 in an attribute column is the
same as _= 10. As we will see shortly, ¬ under the relation name denotes (a limited form of) ¬
in the relational calculus sense.

6.5 Overview of Design Process

Our primary focus is the design of the database. The database design process can be divided into
six steps:
Requirements Analysis

The very first step in designing a database application is to understand what data is to be stored
in the database, what applications must be built on the database, and what operations must be
performed on the database. In other words, we must find out what the users want from the
database. This process involves discussions with user groups, a study of the current operating
environment, how it is expected to change an analysis of any available documentation on
existing applications and so on.

Conceptual Database Design

The information gathered in the requirement analysis step is used to develop a high-level
description of the data to be stored in the database, along with the conditions known to hold this
data. The goal is to create a description of the data that matches both—how users and developers
think of the data (and the people and processes to be represented in the data). This facilitates
discussion among all the people involved in the design process i.e., developers and as well as
users who have no technical background. In simple words, the conceptual database design phase
is used in drawing ER model.

Logical Database Design

We must implement our database design and convert the conceptual database design into a
database schema (a description of data) in the data model (a collection of high-level data description
constructs that hide many low-level storage details) of the DBMS. We will consider only relational
DBMSs, and therefore, the task in the logical design step is to convert the conceptual database
design in the form of E-R Schema (Entity-Relationship Schema) into a relational database schema.

Schema Refinement

The fourth step in database design is to analyze the collection, of relations (tables) in our
relational database schema to identify future problems, and to refine (clear) it.
Physical Database Design

This step may simply involve building indexes on some tables and clustering some tables, or it
may involve redesign of parts of the database schema obtained from the earlier design steps.

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