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 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 in order to support the business.
2. The Entity-Relationship Diagram is also used to identify the data required to derive and generate 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

Entities: Entities are objects or concepts within the data model. Each entity is represented by a box with in the ERD.  An entity might be considered a container that holds all of the instances of a particular thing in a system.

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.

Relationship: A relationship is an association among the instances of one or more entity types that is of interest to the organization. A relationship is the association between entities or entity occurrence

Cardinality: The cardinality defines the relationship between the entities in terms of numbers.

EVALUATION

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

Types of cardinality relationship

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

• One-to-One Relationship
• One-to-Many Relationship
• Many-to-Many Relationship

GENERAL EVALUATION

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

READING ASSIGNMENT

Data Processing for Senior Secondary Education Hiit Plc. Chapter Four Pgs69 – 70.

WEEKEND ASSIGNMENT

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

1. ____ is the unique, distinguishing characteristic of the entity.
2. Entity         B. Relationship             C. Attribute     D. cardinality
3. Another name for data Element is ____.
4. Attribute   B. Key               C. Entity           D. Relationship
5. ____ are objects or concepts within the data model.
6. Attributes  B. Relationship             C. Cardinality               D. Entity
7. A roof covering a building will be considered in relationship as?
8. One-to-Many
9. Many-to-Many
10. One-to-One
11. Many-to-One
12. A pastor preaching to his congregation will be considered in relationship as?
13. One-to-Many
14. Many-to-Many
15. One-to-One
16. Many-to-One

SECTION B

1. List with example, the types of cardinal relationship.
2. State the uses of entity-relationship diagram.