Re: [Asdf] Extension point mechanism thoughts

[Michael Koster <[e-mail]>]

Is there a well defined way to merge schema fragments into a schema at schema-defined places? For JSO we could use JSON pointer (JSON path would be more robust...) and JSON merge-patch behavior; what about cddl?

> On Mar 30, 2022, at 8:20 AM, Michael Koster <[e-mail]> wrote:
> 
> One more point, the schema extension mechanism provides for the first stage of development for new language features to be deployed in an organized way. 
> 
> For example, ext:meta could be the larval stage of a proposal for a built-in category "sdfMeta" in a later version of SDF. 
> 
> 
>> On Mar 30, 2022, at 8:08 AM, Michael Koster <[e-mail] <mailto:[e-mail]>> wrote:
>> 
>> I intended to add another entity to the schema that works in the same way as sdfData and can be applied to any definition, but is intended to provide named metadata items to any definition.
>> 
>> It'sr a way of adding a category as an extension, rather than a simple quality.
>> 
>>> On Mar 30, 2022, at 7:51 AM, Michael Koster <[e-mail] <mailto:[e-mail]>> wrote:
>>> 
>>> 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 <https://example.com/sdfextension>" }
>>> 
>>> at https://example.com/sdfextension <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 ):
>>> 
>> should say category, not quality, and it needs to be added to thingqualities, objectqualities, proertyqualities, actionqualities, and eventqualities
>>> {
>>>   id: https://example.com/sdfextension <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.
>>> 
>>> 
>>> 
>> 
>