Define TD Fragment

[mlagally]

Adding TD Fragment definition as proposed in arch call 2 weeks ago.
May need some minor editorial changes.

resolves #574

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[mmccool]

Note: "JSON Fragment" has been defined as a JSON element that is not an object or array, e.g. a basic value like a string or number. A TD Fragment could be a JSON Fragment (i.e. just a string) but it MIGHT also be an object or array (eg a DataSchema) (at least in the Discovery use case).

We have to decide if the name will be confusing because of this. If we feel it would be, we might want to pick another name. Options might include "TD Component", "TD Element", or "TD Node". "Component" may conflict with names we might want to use later for modularity, though. "Node" may conflict with use of this term in RDF. So if we DO have to change the name, I'd vote for "TD Element". We might also want to see if there is a definition in JSON for the concept we want and use that to align better with JSON.

Update: I looked at various JSON docs and it seems "Element" is used with the meaning we want (superclass of Arrays, Objects, and (JSON) Fragments).

[mmccool]

Should replace reference to "chapter 5" with a link that uses the section name (eg "Information Model"). Also, the link should probably not be an actual link, but a reference.

[mlagally]

@mmccool Please provide an appropriate link

[mmccool]

Direct link should be a reference. It might also be helpful to mention a particular section or link to an example.

[mlagally]

@mmccool Please provide an appropriate link

[danielpeintner]

Question. Is the following a valid TD fragment? It is not valid JSON...

"status": {
    "type": "string"
}

[mmccool]

"the fragment" perhaps should be "the TD Fragment" to be consistent with other usages

[mmccool]

BTW, some refs for JSON, although I can't find definitions of "JSON fragment" or "JSON element" in there. I will do a bit more research; these do seem to be common terms, but may not be in the official standards:

• IETF RFC 8259
• ECMA-404

[mlagally]

BTW, some refs for JSON, although I can't find definitions of "JSON fragment" or "JSON element" in there. I will do a bit more research; these do seem to be common terms, but may not be in the official standards:

• IETF RFC 8259
• ECMA-404

ECMA-404 defines the "JSON Value" grammar, which I think is what we want to call "JSON Element"

I came across the following "JSON fragment" definition (https://medium.com/grand-parade/creating-type-safe-json-in-swift-74a612991893), which may be useful:

A JSON fragment is a JSON that does not have an Object or an Array as the root.

[danielpeintner]

I came across the following "JSON fragment" definition (https://medium.com/grand-parade/creating-type-safe-json-in-swift-74a612991893), which may be useful:

A JSON fragment is a JSON that does not have an Object or an Array as the root.

I think there are different interpretations what a fragment is.

• part of a TD (not complete according to JSON schema)
• sub-part of a a TD (a inner element like just a given property)
• a JSON that per se is not valid (e.g., multiple objects on root level OR "status": {"type": "string"} )
• combinations of the aforementioned

[mlagally]

Arch call on 11.2.
We merged the definition from the later MR #580 , this MR is obsolete but the branch will be kept for documentation purposes.