When you create an object, Creo Elements/Direct Modeling assigns a unique identifier, called the SysID, to the object. The SysID of an object is a primary key and never changes even if the object is modified many times in different sessions. Creo Elements/Direct Modeling uses the symbolic version of an object as a secondary key to distinguish between different versions of the same object in a session. Finally, the symbolic name is an alternative (primary) key. The symbolic name allows Creo Elements/Direct Modeling to recognize semantically-similar objects for substitution.

As objects are stored in separate files, parent-child relationships between objects are represented by external references. Every parent object stores references to its direct child objects. Child objects do not store any information about their parent objects.

When an assembly is loaded from multiple files, the assembly structure needs to be rebuilt in the session. The references need to be resolved, that is, the references must be mapped to the appropriate child objects. This process is only based on the SysID, symbolic name, and symbolic version. Neither the filenames nor the names of the objects play any role in resolving the references.

The highest criterion to map a reference to its object is a matching SysID. Symbolic versions are then used to resolve further ambiguities, if any. If a matching SysID is not found, symbolic names are used to locate alternative objects.