Primary Keys for Relationship Sets

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Primary Keys for Relationship Sets

The attributes of a relationship set are the attributes that comprise the primary keys of the entity sets involved in the relationship set.

For example:

This is enough information to enable us to relate an account to a person.

If the relationship has descriptive attributes, those are also included in its attribute set. For example, we might add the attribute date to the above relationship set, signifying the date of last access to an account by a particular customer.

Note that this attribute cannot instead be placed in either entity set as it relates to both a customer and an account, and the relationship is many-to-many.

The primary key of a relationship set depends on the mapping cardinality and the presence of descriptive attributes.

With no descriptive attributes:

Descriptive attributes may be added, depending on the mapping cardinality and the semantics involved (see text).

Page created and maintained by Osmar R. Zaï ane
Last Update: Sun Sep 10 17:02:35 PDT 1995