Relationship property sheet Cardinalities tab

Chapter 3 Building Conceptual Data Models

Relationship property sheet Cardinalities tab

The Cardinalities tab contains the following properties:

Property	Description
Cardinality	Specifies the number of instances (none, one, or many) of an entity in relation to another entity. You can choose from the following values: One-to-one (symbol: <1..1>) - One instance of the first entity can correspond to only one instance of the second entity One-to-many (symbol: <1..n>) - One instance of the first entity can correspond to more than one instance of the second entity Many-to-one (symbol: <n..1>) - More than one instance of the first entity can correspond to the same one instance of the second entity Many-to-many (symbol: <n..n>) - More than one instance of the first entity can correspond to more than one instance of the second entity

Property

Description

Cardinality

Specifies the number of instances (none, one, or many) of an entity in relation to another entity. You can choose from the following values:

One-to-one (symbol: <1..1>) - One instance of the first entity can correspond to only one instance of the second entity
One-to-many (symbol: <1..n>) - One instance of the first entity can correspond to more than one instance of the second entity
Many-to-one (symbol: <n..1>) - More than one instance of the first entity can correspond to the same one instance of the second entity
Many-to-many (symbol: <n..n>) - More than one instance of the first entity can correspond to more than one instance of the second entity

In addition, this tab contains a groupbox for both directions of the relationship, each of which contains the following properties:

Property	Description
Dominant role	In a One to One relationship, indicates to generate a reference in the PDM for this direction of the relationship only.
Role name	Text that describes the relationship of EntityA to EntityB.
Dependent	Indicates that each instance of the EntityA is identified by an instance of EntityB.
Mandatory	Indicates that each instance of the EntityA requires an instance of the EntityB.
Cardinality	Specifies the maximum and minimum number of instances of EntityA in relation to EntityB (if mandatory, at least 1). You can choose from the following values: 0..1 – Zero to one instances 0..n – Zero to many instances 1..1 – Exactly one instance 1..n – one to many instances

Termination points

In a diagram, termination points indicate cardinality at each end of a relationship. A termination with a single contact point denotes a cardinality of one. A termination with three contact points denotes a cardinality of many.

Termination point	Cardinality
	One
	Many

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

Example

The Cardinalities page below indicates that an employee must belong to one and only one division, while a division must include one or more employees.