Page 97 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Database Management Systems/Managing Database

Notes Application and Security Design

Any software project that involves a DBMS must consider applications that involve processes
and identify the entities.

Example: Users, user groups, departments, etc. We must describe the role of each entity
in every process. As a security design, for each role, we must identify the parts of the database
that must be accessible and the parts of the database that must not be accessible and we must take
steps to ensure that these access rules are enforced. In general, our division of the design process
into six steps are repeated until the design is satisfactorily known as tuning phase.

6.6 Entity-Relationship Model

The entity-relationship (ER) data model allows us to describe the data involved in real-world
enterprise in terms of objects (entities) and their relationships, and is widely used to develop an
initial database design.
The ER model is important for its role in database design. It provides useful concepts that allows
to change the detailed and informal description of what users want to a precise and formal
description that can be implemented in a DBMS. Within the overall design process, the ER
model is used in a phase called Conceptual database design.
Even though the ER model describes the physical database model, it is basically useful in the
design and communication of the logical database model,

The overall logical structure of a database can be expressed graphically by an E-R diagram as
follows:

Figure 6.1: Entity-relationship Diagram

Attr R1 Attr R1
Attrl 1 Attrl 1 Attr 21 Attr 2k

ENTITY1 RELATIONSHIP ENTITY2

The E-R diagram is built up from the following components:
1. Rectangles: Which represent entity sets.
2. Diamonds: Which represent relationships among entity sets, which are connected to the
rectangles by lines.
3. Ellipses: Which represent attributes, and are connected to the entities or relationship by
lines.

4. Lines: Which link attributes to entity sets and entity sets to relationships.
The rectangles, diamonds and ellipses are labelled with the entity, relationships and attributes,
respectively, that it represents.

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