Conceptual Design Using the ER Model
Design choices:
- Should a concept be modelled as an entity or an attribute?
- Should a concept be modelled as an entity or a relationship?
- Identifying relationships: Binary or ternary?
Constraints in the ER Model:
- A lot of data semantics can (and should) be captured.
- But some constraints cannot be captured in ER diagrams.
Need for further refining the schema:
- Relational schema obtained from ER diagram is a good first step. But ER design subjective & can’t express certain constraints; so this relational schema may need refinement.