Model refactoring based on feedback (Session 1)

[david-waltermire]

Committer Notes

Work on multiple issues described by the epic #597.

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you squashed any non-relevant commits and commit messages? [instructions]
• Do all automated CI/CD checks pass?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you included examples of how to use your new feature(s)?
• Have you updated all OSCAL website and readme documentation affected by the changes you made? Changes to the OSCAL website can be made in the docs/content directory of your branch.

[david-waltermire]

I mistakenly referenced #518 when I intended to reference #581.

[bradh]

This doesn't appear at https://www.iana.org/assignments/link-relations/link-relations.xhtml (although the previous one didn't either).

[david-waltermire]

We use rels that are not in the link relations IANA registry. I think we need to come up with a means for the IANA relations and the OSCAL relations to co-exist.

[david-waltermire]

PR #619 includes these changes. Closing this PR.