Entity–Relationship Models

Back to: DATA PROCESSING SS 2

 

Welcome to class! 

In today’s class, we will be talking about entity-relationship models. Enjoy the class!

Entity–Relationship Models

Entity-Relationship is a graphical representation of entities and their relationships to each other. Entity-relationship diagrams (ERDs) illustrate the logical structure of the database. Diagrams created to design these entities and relationships are called entity-relationship diagrams or ER diagram.

Uses of Entity-Relationship diagram

1. The Entity-Relationship Diagram is used to identify the data that must be captured, stored and retrieved to support the business.
2. The Entity-Relationship Diagram is also used to identify the data required to derive and generate a report on the performance measures that an organization should be monitoring.

Components of Entity-Relationship

Entity- Relationship diagrams have three different components;

• Entities
• Attributes
• Relationships

1. Entities: Entities are objects or concepts within the data model. Each entity is represented by a box within the ERD.  An entity might be considered a container that holds all of the instances of a particular thing in a system.
2. Attributes: a key attribute is the unique, distinguishing characteristics of the entity. Primary key is always the attribute of ER. Entities are further described by their attributes (sometimes called data element). These are the smallest units of data that can be described in a meaningful manner.
3. Relationship: A relationship is an association among the instances of one or more entity types that are of interest to the organization. A relationship is an association between entities or entity occurrence
4. Cardinality: The cardinality defines the relationship between the entities in terms of numbers.

Evaluation

1. Define the following; Entity, Attribute and relationship.
2. State the uses of an entity-relationship diagram.

Types of cardinality relationship

There are potentially three types of relationship which can exist between different entities;

1. One-to-One Relationship
2. One-to-Many Relationship
3. Many-to-Many Relationship

General evaluation

1. What is Cardinality?
2. Mention and explain three types of relationship with example.

Weekend assignment

Instruction: Choose the correct option from the ones lettered A to D

1. ____ is the unique, distinguishing characteristic of the entity. A. Entity      B. Relationship  C. Attribute  D. cardinality
2. Another name for data Element is ____. A. Attribute     B. Key     C. Entity        D. Relationship

Section B

1. List with example, the types of cardinal relationship.
2. State the uses of an entity-relationship diagram.
3. Using tables, explain the differences between primary key and foreign key.
4. State two characteristics of suitable relations that support the data requirements of an enterprise.

 

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