IRI expansion within @context requires terms to be previously defined about json-ld.org

[gkellogg]

The problem comes to play when an author wants to create a context both defining terms and using them in @datatype. For example:

@context: {
  "xsd": "http://www.w3.org/2001/XMLSchema#",
  "date": {"@iri": "http://purl.org/dc/terms/date", "@datatype": "xsd:date"}
}

This requires two passes over @context, first to resolve prefixes, and second to use those prefixes in @datatype declarations. Note that before, when @Coerce was a separate object, this processing was in effect; it was lost when we folded in datatypes with prefix definitions.

As a related issue, we could consdier the following:

@context: {
  "xsd": "http://www.w3.org/2001/XMLSchema#",
  "dc": "http://purl.org/dc/terms/",
  "date": {"@iri": "dc:date", "@datatype": "xsd:date"}
}

This adds another layer of complication, as it may require more than two passes to resolve the use of CURIEs in @iri definitions, so I would not go this far, although the use of a CURIE should be allowed, if it is defined in an outer context.

I believe that we should adopt the first form, as it is a natural way to create a context for authors, and there is a reasonable possibility that there will be errors if authors do not separate prefix definitions from the usage in datatypes.

I propose that we formally say that context object traversal is a two-pass operation, where first IRIs for defined terms are identified and then @datatype and @list processing occurs, so that prefixes defined within a context can be used for @datatype definitions.

As an alternative, we could define a set of terms that are defined in a global "default" context, similar to RDFa's default context. There we could define mappings for xsd, rdf, dc, foaf, schema and others. This would eliminate most need for doing two-pass processing of contexts.

[lanthaler]

Demo in PHP supporting CURIEs in @iri and @datatype: https://github.com/lanthaler/JSON-LD-experiments/blob/master/context-coerce-merge.php

-----Original Message-----
From: Gregg Kellogg [mailto:reply+i-2273041-
[email protected]]
Sent: Friday, November 18, 2011 4:00 AM
To: Markus Lanthaler
Subject: [json-ld.org] IRI expansion within @context requires terms to
be previously defined (#41)

The spec describes defining an @context in terms of having an "active
context". This allows terms and prefixes to be used within a @context
definition, if they are defined earlier.

Update the spec to ensure that this is clear, and to allow both from
contexts defined in a higher object, and those that precede within an
array of contexts.

---

Reply to this email directly or view it on GitHub:
#41

[lanthaler]

@gkellogg, what about using prefixes defined in the local context in @iri? Is that allowed or not? In my opinion it would make sense to allow that as well.

[gkellogg]

That creates some circularity, as you may need to process n-1 times to resolve everything. It was easier to just require full IRis. If you can think of reasonable language in Context handling, we could consider this.

[lanthaler]

OK, I will try to come up with something. I'm not sure though if I'll be able to do that before Christmas..

-----Original Message-----
From: Gregg Kellogg [mailto:reply+i-2273041-
[email protected]]
Sent: Thursday, December 15, 2011 10:38 PM
To: Markus Lanthaler
Subject: Re: [json-ld.org] IRI expansion within @context requires terms
to be previously defined (#41)

That creates some circularity, as you may need to process n-1 times to
resolve everything. It was easier to just require full IRis. If you can
think of reasonable language in Context handling, we could consider
this.

---

Reply to this email directly or view it on GitHub:
#41 (comment)

[lanthaler]

RESOLVED: IRI expansion should work in @context for prefixes and terms used on the right-hand side of prefix/term declarations, including @type and @id. The IRI expansion algorithm SHOULD be recursive, in that it continues to execute as long as one prefix/term is expanded in the current cycle. If a cycle is detected during resolution, then an exception MUST be thrown.

[msporny]

http://json-ld.org/spec/ED/json-ld-syntax/20120122/#iri-expansion-within-a-context