Chapter 4 Building Conceptual Data Models


Defining relationships in a CDM

A relationship is a link between entities. For example, in a CDM that manages human resources, the relationship Member links the entities Employee and Team, because employees can be members of teams. This relationship expresses that each employee works in a team and that each team has employees.

An occurrence of a relationship corresponds to one instance of each of the two entities involved in the relationship. For example, the employee Martin working in the Marketing team is one occurrence of the relationship Member.

Relationships and association

Relationships are used in the Entity Relationship (ER) and IDEF1X modeling methodologies. In PowerDesigner you can also use associations used in the Merise methodology to link entities. You can use either relationships or associations exclusively, or combine the two methodologies in the same model.

For more information on using associations, see section Defining associations in a CDM.

This section analyzes relationships in the Entity Relationship methodology, for more information on IDEF1X, see section CDM Options in chapter Conceptual Data Model Basics.

 


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