Week 3

3.2 Attributes

An ATTRIBUTE is a property or characteristic of an entity type. In ER diagrams, attributes are represented as OVALS connected to their entity type.

Attribute Type	Definition and Example
Simple (Atomic)	Cannot be divided further. E.g., StudentID, DateOfBirth, GPA
Composite	Can be divided into smaller sub-parts. E.g., Address → (StreetNo, StreetName, LGA, State). E.g., FullName → (FirstName, MiddleName, LastName)
Multi-valued	Can have multiple values for one entity. E.g., a Lecturer may have multiple PhoneNumbers. Drawn as DOUBLE OVAL.
Derived	Value is computed from other attributes. E.g., Age derived from DateOfBirth; TotalCreditUnits derived from registered courses. Drawn as DASHED OVAL.
Key Attribute	Uniquely identifies each entity instance. E.g., MatricNumber for STUDENT. Underlined in ER diagram.
Null Attribute	May have no value for some instances. E.g., MiddleName may be absent for some students.