Use of Extended E-R Features

We have seen weak entity sets, generalization and aggregation. Designers must decide when these features are appropriate.

• Strong entity sets and their dependent weak entity sets may be regarded as a single ``object'' in the database, as weak entities are existence-dependent on a strong entity.
• It is possible to treat an aggregated entity set as a single unit without concern for its inner structure details.

• Generalization contributes to modularity by allowing common attributes of similar entity sets to be represented in one place in an E-R diagram.