Database Reference
In-Depth Information
4. What do you mean by a relation?
5. What is ER diagram?
6. What is the goal of ER Modeling?
7. What do you mean by domain of Attributes?
8. What do you mean by Relationships?
9. Explain following terms
a. 1:1 relationships
b. 1:M relationships
c. M:1 relationships
d. M:M relationships
e. Unary Relationships
10. What is mapping?
11. Explain various mapping rules for Entity Diagram with suitable examples.
12. How do you map relationships?
Chapter 4
RELATIONAL MODEL
4.1 INTRODUCTION
The relational data model is unusual in being largely due to the efforts of one man, E.F.
Codd. In 1970 E.F. Codd published a seminal paper which laid the foundation for prob-
ably the most popular of the contemporary data models. A database is effectively a set of
data structures for organising and storing data. In any data model, and consequently in any
DBMS, we must have a set of principles for exploiting such data structures for information
systems applications with in organisations. Data definition is the process of exploiting the
inherent data structures of a data model for a particular organisational application.
4.2 DOMAINS
Each column of a table there is a set of possible values called its domain. The primary unit
of data in the relational data model is the data-item. Such data-items are said to be non-de-
composable or atomic. A set of such data-items of the same type is said to be a domain.
Domains are therefore pools of values from which actual values appearing in the columns
of a table are drawn.
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