Canonical URL Restrictions (Round 1)

[snyaggarwal]

Some of the quick wins:

• Always present -- generate/auto-populate
• Unique across system
• Restrict Update? (if editable, then we will have to update all the references in collections)
• Repo Versions to have the exact same canonical URL as HEAD (might already be working, need to write a test for this)

Current state:

• Must be a URI
• No rules to enforce uniqueness of a canonical URL within a namespace
• Updating a canonical URL will likely break things... different repo versions would have different canonical URLs
  • Scenario: Released multiple repo versions and then set/change a canonical URL -- does it apply only to HEAD and new versions, or does it apply to prior versions?
• Some operations are only available if a canonical URL is set:
  • for $resolveReference namespace only relevant if canonical is present
  • some expansion params require canonical (system-version, exclude-system)
• No global canonical URL registry, so evaluation of canonical references may be ambiguous if multiple repos (in different namespaces) share the same canonical