ER diagrams.

used to represent data entities, entity attributes , relationships

Entity is an object we keep information about.

Example. Students, Subjects, Marks

Attributes are Properties of entities. 

Student Name, Age, Index No are attributes of Student Entity



Types of Attributes

Simple attribute : cannot be divided further. phone number is 10 digits.

Composite attribute : made of more than one simple attribute. The student's full name has a first and last name.

Derived attribute: the attributes that do not exist in the physical database, but their values are derived from other attributes present in the database. Age can be derived from the date of birth.

Single-value attribute : contain single value. ID Number.

Multi-value attribute : contain more than one values.
home phone number, work phone number

Relationships:
Relationships are logical links between two or more entities.
Teching is a relationship that can exist between a teacher and student



1. Describe 3  Entities 
2. Describe 5 entities for each
3. For each entity identify simple, composite, derived and multi-valued entities.
4. Describe relationships between entities.