ENTITY RELATIONSHIP MODEL
CONTENT
- Entities, Attributes and Relationships
- Additional Features of Entity Model
Entities, Attributes and Relationships
The rectangle in the diagram above are called entity type and the ovals are called attributes. The entities are the ‘things’ in the business environment about which we want to store data. The attributes provide us with a means of organizing and structuring the data.
Entities
Entities are drawn as rectangular boxes containing a noun in the singular form.
You will see later that each entity you draw ultimately becomes a table in your database. You might want to keep this transformation from entity to table in mind when selecting the names of your entities. E.g. your entity names should be short but descriptive.
Relationship
A relationship between entities is drawn as a line bisected by a diamond. The diamond contains a verb (or short verb phrase) that describes the nature of the relationship between the entities.
Named relationships are used to make the ERDs more readable. However, unlike entity names, relationship names never show up in the final database.
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