Relationship Property Sheet Cardinalities Tab

The Cardinalities tab allows you to specify the nature of the relationship between the two entities.

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 entity A can correspond to only one instance of entity B. One-to-many (symbol: <1..n>) - One instance of entity A can correspond to more than one instance of entity B. Many-to-one (symbol: <n..1>) - More than one instance of entity A can correspond to the same one instance of entity B. Many-to-many (symbol: <n..n>) - More than one instance of entity A can correspond to more than one instance of entity B. To use n..n relationships in an LDM, see Enabling many-to-many relationships in an LDM.
Dominant role	[one-to-one relationships only] Specifies one direction of the relationship as dominant. If you define a dominant direction, the one-to-one relationship generates one reference in a PDM, with the dominant entity as the parent table. If you do not define a dominant direction, the one-to-one relationship generates two references. In the following example, the author is the dominant entity: In a PDM, this relationship generates a reference with Author as the parent table, and its primary key migrated to the Picture table as a foreign key:

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 entity A can correspond to only one instance of entity B.
One-to-many (symbol: <1..n>) - One instance of entity A can correspond to more than one instance of entity B.
Many-to-one (symbol: <n..1>) - More than one instance of entity A can correspond to the same one instance of entity B.
Many-to-many (symbol: <n..n>) - More than one instance of entity A can correspond to more than one instance of entity B. To use n..n relationships in an LDM, see Enabling many-to-many relationships in an LDM.

Dominant role

[one-to-one relationships only] Specifies one direction of the relationship as dominant. If you define a dominant direction, the one-to-one relationship generates one reference in a PDM, with the dominant entity as the parent table. If you do not define a dominant direction, the one-to-one relationship generates two references.

In the following example, the author is the dominant entity:

In a PDM, this relationship generates a reference with Author as the parent table, and its primary key migrated to the Picture table as a foreign key:

For information about the termination points of the relationships in each of the supported notations, see Supported CDM/LDM Notations.

In addition, this tab contains a groupbox for each direction of the relationship, containing the following properties:

Property	Description
Role name	Text that describes the relationship of EntityA to EntityB, and which is used to generate the assertion statements displayed at the top of this tab. You should use the infinitive phrase that describes the relationship of one entity to the other. For example, `Each Order may contain one or more line.`, and `Each line must belong to one and only one Order.` To modify the sentences generated from your role names, edit your model's assertion template (see Assertion Template).
Dependent	Specifies that the entity is dependent on and partially identified by the other entity. In the following example, the task entity is dependent on the project entity. Each task is a part of a project and each project can contain zero or more tasks:
Mandatory	Specifies that each instance of the entity requires at least one instance of the other entity. For example, the subcontract relationship is optional from customer to project, but mandatory from project to customer. Each project must have a customer, but each customer does not have to have a project. Implied by dependent
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