Chapter 4 Building Conceptual Data Models

Defining a mandatory relationship

The property Mandatory indicates whether the relationship between entities is mandatory or optional. You define options from the point of view of both entities in the relationship.

Termination points

In the resulting relationship symbol, a bar represents a mandatory relationship. A circle represents an optional relationship.

Termination point	Existence	Cardinality	Description
	Mandatory	One	Must exist one and only one
	Mandatory	Many	Must exist one or more
	Optional	One	May exist one, or none
	Optional	Many	May exist one or more, or none

For more information on IDEF1X existence notation, see section CDM options in chapter Conceptual Data Model Basics.

To define a mandatory relationship:

1. Double-click the relationship symbol to display the relationship property sheet.
2. Click the Cardinalities tab to display the corresponding page.
3. Select the Mandatory check box in one or both of the groupboxes corresponding to a relationship direction.
4. Click OK.

Example

The Cardinalities page below indicates that the subcontract relationship is optional from customer to project, and mandatory from project to customer. Each project must have a customer, while each customer does not have to have a project.

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