About Reference Types
A reference is indicated by an arrow between two objects in the Parent/Child graph. When there is more than one reference, the number of references appears on the arrow. With the Reference Viewer you can investigate the following reference types:
Regular References
Regular references are created between features in the context of a single part or in the context of an assembly. Feature references can be local or external. Local references are created by features that only reference geometry of the model in which they were created. When you create an assembly feature, local references are created to geometry of assembly components. External references are created by a feature referencing geometry that does not belong to the model where the feature is created.
External references are indicated by a gray dot on the reference arrow in the Parent/Child graph.
Relation References
Relation references are equations written between dimensions and parameters to define relationships within features or parts, or among assembly components. You can investigate model and feature relations, and you can investigate local and external references created by relations.
Placement References
Placement references are used to place a component in an assembly. When a part is added to an assembly, the system creates a component feature called a Placement folder. The folder stores the part name and the part and assembly entities that were used to place the part.
System References
As opposed to explicit references created when you select a reference, system references are created implicitly following a feature definition or topology dependency. One exception to this is an external copy geometry feature. Following are two examples of operations that create system references.
When you create a hole on a surface and later create another hole that intersects the first hole. The geometry of the second hole is affected by the geometry of the first hole, automatically generating a system reference.
When you select one edge of a chain, all edges of the chain are automatically collected following the request to select a chain. Despite the fact that these edges were not explicitly selected, the feature depends on them and they are considered system references.