Relative IRIs may clash with terms

[niklasl]

Altough we've removed @base, the issue remains where relative IRIs (who seem to be still supported) and terms may clash. For instance, consider this data (assuming it is located at http://example.org/):

{
  "@context": {"homepage": "http://xmlns.com/foaf/0.1/homepage"},
  "@id": "homepage#me",
  "homepage": {"@id": "homepage"}
}

Currently, the triple for this data would become:

<http://example.org/homepage#me>
    <http://xmlns.com/foaf/0.1/homepage> <http://xmlns.com/foaf/0.1/homepage> .

Not the intended:

<http://example.org/homepage#me>
    <http://xmlns.com/foaf/0.1/homepage> <http://example.org/homepage> .

This is because the @id given for homepage would be found among the terms and not be resolved against "http://example.org/".

There are various ways of resolving this:

1. Only allow full IRIs. That will probably be problematic since there are many good use cases for them, e.g. for referencing contexts, and if nothing else it is most certainly common practise for linking on the web.
2. Not allow relative IRIs that might be confused with terms, e.g. by requiring non-full IRI paths to start with either "/" (i.e. be absolute) or "./" (which is already a requirement in the URI spec if the first segment contains a colon, to disambiguate from a protocol). This could work but perhaps suffers in part of the problems of 1 (since it isn't uncommon for relative links to be given as only the leaf segment of a path).
3. Don't allow terms or CURIEs as values in @id (including for coerced values). That's problematic since there are many needs for these, both in contexts and in certain instance data cases for referencing e.g. classes and properties (and as @type is basically defined as {"@id": "rdf:type", "@type": "@id"}). We could have two different keywords, one for taking TERMorCURIEorAbsIRI values (mainly used in coercion, possibly named @term), and one for only IRIs or perhaps CURIEorIRI. (See RDFa 1.1 for the definitions of these.)

[lanthaler]

I don't think option 1 is not viable since often it's difficult for a service to figure out its base IRI. E.g. this would make serving a collection of JSON-LD documents over CDN impossible.

Option 2 seems to be a good idea as because it makes the intent very clear. I, e.g., would have classified the above example as correct - I would have seen that as my intent. But that's probably just because of the strange value "homepage".

Option 3 could work but, as you said, is problematic.

So summarized I tend to support option 2. Relative IRIs seem to be problematic also in another instance, see issue #56. Option 2 could solve this problem as well I think. The only open problem would then be a the use of an unspecified prefix which would be interpreted as a schema, but I can't see anything we could do about that.

Btw, I think misread the URI spec - if I'm not completely off:

relative-ref = relative-part ...
relative-part = ... / path-no-scheme / ..
path-no-scheme = segment-nz-nc ( "/" segment )
segment-nz-nc = 1( unreserved / pct-encoded / sub-delims / "@" )
; non-zero-length segment without any colon ":"
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"

So it can start with any character. The first segment just can't contain a colon.

-----Original Message-----
From: Niklas Lindström [mailto:reply+i-2793880-
7ce675672543f0c89f7683a1586ab8e5b60dfc8f-456407@reply.github.com]
Sent: Wednesday, January 11, 2012 1:16 AM
To: Markus Lanthaler
Subject: [json-ld.org] Relative IRIs may clash with terms (#49)

Altough we've removed @base, the issue remains where relative IRIs
(who seem to be still supported) and terms may clash. For instance,
consider this data (assuming it is located at http://example.org/):

{
  "@context": {"homepage": "http://xmlns.com/foaf/0.1/homepage"},
  "@id": "homepage#me",
  "homepage": {"@id": "homepage"}
}

Currently, the triple for this data would become:

<http://example.org/homepage#me>
    <http://xmlns.com/foaf/0.1/homepage>

http://xmlns.com/foaf/0.1/homepage .

Not the intended:

<http://example.org/homepage#me>
    <http://xmlns.com/foaf/0.1/homepage>

http://example.org/homepage .

This is because the @id given for homepage would be found among the
terms and not be resolved against "http://example.org/".

There are various ways of resolving this:

1. Only allow full IRIs. That will probably be problematic since there
   are many good use cases for them, e.g. for referencing contexts, and if
   nothing else it is most certainly common practise for linking on the
   web.
2. Not allow relative IRIs that might be confused with terms, e.g. by
   requiring non-full IRI paths to start with either "/" (i.e. be
   absolute) or "./" (which is already a requirement in the URI
   spec if the first
   segment contains a colon, to disambiguate from a protocol). This could
   work but perhaps suffers in part of the problems of 1 (since it isn't
   uncommon for relative links to be given as only the leaf segment of a
   path).
3. Don't allow terms or CURIEs as values in @id (including for
   coerced values). That's problematic since there are many needs for
   these, both in contexts and in certain instance data cases for
   referencing e.g. classes and properties (and as @type is basically
   defined as {"@id": "rdf:type", "@type": "@id"}). We could have two
   different keywords, one for taking TERMorCURIEorAbsIRI values (mainly
   used in coercion, possibly named @term), and one for only IRIs or
   perhaps CURIEorIRI. (See [RDFa 1.1](http://www.w3.org/TR/rdfa-
   core/#s_datatypes) for the definitions of these.)

---

Reply to this email directly or view it on GitHub:
#49

[dlongley]

+1 for option 2.

[lanthaler]

Issue #46 might be related to this, especially the need for IRI normalization.

[lanthaler]

2012-01-24 Telecon:

RESOLVED: The lexical space for keys in JSON-LD key-value statements is if a term: NCName, if a prefix: NCName for the prefix, otherwise the lexical space for an IRI.

RESOLVED: The lexical space for keys in JSON-LD Context key-value statements is if a term: NCName, if a prefix: NCName for the prefix, otherwise the lexical space for an absolute IRI.

[gkellogg]

Also completed in d3c4996.