Page 108 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Unit 6: Relational Language and Database Design

Notes
Figure 1: ER Diagram of COMPANY Database

IName PremAmount
Phone
PolicyNo
Addr PolicyName MatName
Age
Tenure
Customers 1 Hold M Policy
Bonus
M Date
Interact

Phone
StaffID 1
M
StaffName 1 Branches
Staff WorkFor
Age
Branch Addr

Phone BranchName

Managers SectAssts DevOfficers FullTime Agents

Step-3: Relationship Sets

As per the requirements as stated already, the following relationship sets may be identified:
1. WorksFor Staff and Branches N: 1 Total on either side
2. Interacts Staff and Customers 1:N Total on either side

3. Hold Customers and Policy 1: N Total on either side
4. Staff (Managers, SectAssts, DevOfficers) IS-A Relationship
5. Staff (FullTime, Agents) IS-A Relationship

6.12 Summary

Relational algebra is a procedural language. It provides a collection of operations to manipulate
relations. It supports the notion of a query which is a request to retrieve information from a
database. The relational algebra data operations and their corresponding operators are:

Basic Operations:
Selection Select Operator ( )
Projection Project Operator ( )

Cross-product Cartesian product (×)
Union Operator ( )
Set Difference Difference Operator (–)

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