Definition

The following constraints apply to link objects:

1. Under any single <Aggregate Feature> instance or <Aggregate Geometry> instance, the link objects (if any) shall have non-identical field values or components, as appropriate. In the case of <Separating Plane Related Geometry> instances, this constraint applies to the link objects of the <Separating Plane Relations> components of the aggregate, as the aggregate itself does not have link objects.

2. Under any single topology hierarchy, whether a <Feature Topology Hierarchy> instance or <Geometry Topology Hierarchy> instance, the link objects shall have non-identical field values or components, as appropriate.

3. Under any single model instance, whether a <Feature Model Instance> instance or a <Geometry Model Instance> instance, the index field values of the <Model Instance Template Index> link objects shall be distinct.

Rationale

Discriminators shall be distinct in order to allow the user to discriminate between the branches they represent.

However, this does not apply to link objects that exist only to specify sides of a <Separating Plane> instance.

For model instances, the indexes into the <Variable> instances associated with an <Interface Template> instance shall be distinct because no <Variable> instance can be set to more than one value at a time.

Example

1. For a level of detail related aggregation, no two <Base LOD Data> link objects may be identical.

2. For a time related aggregation, two <Time Constraints Data> link objects may overlap, but not be identical.

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