CCB-82: Extend Internal_Reference to Support Explicit Relationship Semantics

[jshughes]

🦄 Sibling SCR

NASA-PDS/PDS4-CCB#82

💡 SCR Summary

This SCR proposes an extension to the PDS4 Internal_Reference class to support explicit modeling of relationships between PDS4 objects. The name of proposed extension is "Internal_Relation".

The Internal_Relation extension will augment Internal_Reference and provide a way to represent a relationship as a first-class association object with two explicit endpoints (Parent and Child), where each endpoint defines:
• the participating object,
• the role it plays in the relationship, and
• the allowed number of participants for that role.

Added to parent epic?

Will do