Metaschema enhancements

[wendellpiez]

User Story:

Currently we have two small requirements not yet addressed by Metaschema:

• Wiring a field or flag to permit only values enumerated in the Metaschema. This feature should permit specifying only a single value (equivalent of FIXED for attributes in XML) but also a selection of permitted values
• Datatype validation on field values

The use case for the first is in #57 - enabling a document to carry an indicator of the version of the schema to which it conforms. (Maybe also which OSCAL model?)

The use case for the second includes citation/href elements (not attributes), to validate they are syntactically correct URIs.

Goals:

Extend Metaschema functionality in both XML and JSON schemas to support these validations.

Making use of them (for #57 or otherwise) is not in scope for this Issue.

Dependencies:

Stable Metaschema.

Acceptance Criteria

The functionality has been developed and demonstrated in testing. A PR has been made to upgrade the metaschema infrastructure.

[wendellpiez]

My current thinking about these -- 1. Some if not all these validations could and perhaps should make good Schematron examples, rather than wiring them into the XSD layer. 2. An outstanding issue is replicating the functionality on the JSON side (this must be mapped out).

So one option is to push these into #400 and subsequently the constraints declaration layer.

[wendellpiez]

2019-06-04 - Given discussion yesterday our plan for representing schema version (#57) and the use of Schematron (#400), this item is not a blocker and could be pushed to M2 or wontfix (if Schematron is always the place to check enumerated values).

[wendellpiez]

Noting that flags with enumerated values already appear in the profile metaschema; the status of this implementation should be checked when/if the functionality is extended to fields.

[david-waltermire]

This issue has been specified at a greater level of detail in issues #436 and #437. I am closing this issue in favor of the other two.