When thinking about what constitutes an entity, it is important not to confuse an aggregate concept, such as an inventory or a medical history, with a single entity.
These aggregates actually represent groups of entities and not single, discrete entities.
Just as business objects have characteristics that describe them, entities are described by their attributes
When we represent an entity in a database, what we actually store are that entitys attributes.
In a nutshell, attributes store data values
- describe or
- identify entities.
Data entered at the intersection of a row (record) and column (field); the data describes or identifies the subject of the record.
Attributes that describe a person (for instance, customer, employee, student, etc.) would include such things as name, address, and telephone number.
Attributes that identify a person would include such things as social security number or any combination of letters and numbers that uniquely identify a person.
- Attributes that describe entities are called non-key attributes.
- Attributes that identify entities (entity identifiers) are called key attributes.
The next lesson explains the purpose of entity identifiers.
Before moving on to the next lesson, click the Exercise link below to test your understanding of entities and attributes.
Entities Attributes - Exercise