[Asdf] Extension point mechanism thoughts

[Michael Koster <[e-mail]>]

If we provide a generalized schema extension mechanism, it should be easy to use it to add a generic extension that applies the dataqualities constraint, and reuse that to provide a more developer-friendly interface that doesn't require the developer to add schema extensions for the simple use case of adding custom metadata to definitions.

extensionNamespace: { ext:" https://example.com/sdfextension" }

at https://example.com/sdfextension we define a schema extension that adds the "meta" quality to commonqualities and applies the existing dataqualities constraint to items that are defined by the new extension ( here in jso language but could also be cddl ):

{
  id: https://example.com/sdfextension 
  schemaextension: ...sdfSchema/commonqualities: { additionalProperties: meta: { $ref:dataqualities } }
}


now we can use ext:meta when we want to attach custom metadata to a definition

sdfThing:

  ObjectTemplate:
    ...
    ext:meta:
      TypeID: 
        type: integer
        minimum: 0
        maximum: 65535
      InstanceID:
        type: integer
        minimum: 0
        maximum: 65535
    # resources, etc.
    sdfProperty: {}
    sdfThing: {}


  Timer:
    sdfRef: /#/sdfThing/ObjectTemplate
    ext:meta:
      TypeID: { const: 43000 }
      InstanceID: { default: 0 }
    # resources, etc.


  TimerInstance:
     sdfRef: /#/sdfThing/Timer
    ext:meta:
      InstanceID: { const: 1001 }
    # resources, etc.