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Re: CURIE syntax thoughts + @instanceof semantics

From: Mark Birbeck <mark.birbeck@x-port.net>
Date: Sun, 16 Dec 2007 17:52:11 +0000
Message-ID: <a707f8300712160952k4ff71669jffde6e061891607c@mail.gmail.com>
To: "Ivan Herman" <ivan@w3.org>
Cc: "W3C RDFa task force" <public-rdf-in-xhtml-tf@w3.org>

Hi Ivan,

I'll come back to the third part of your post separately, but just on
the first two parts, the syntax you suggest is already allowed.

> just try to share some line of thoughts that (1) came to my mind related
> to edge cases of the CURIE syntax and (2) gave me some new ideas related
> to @instanceof. (I hope I could catch your attention:-)
>
> 1. At present, my reading of the CURIE syntax grammar is that the
> following is illegal:
>
> @attribute="prefix:"
>
> Ie, what is called a "reference" in the syntax is _required_. My first
> question is: why? Why can't we say that the value of "prefix:" is, well,
> the URI that is defined for the prefix? Is there any fundamental reason
> for that?

Although the 'reference' part is required, it's a relative URI, and
since an empty value is valid for a relative URI, you get exactly what
you want.

We tried to draw attention to this 'quirky' usage in the CURIEs spec
[1], by giving the following example (see in section 5.1):

  joseki:

Note that this kind of usage means that you could abbreviate complete
URIs so as to make a document and its metadata easier to read and
edit. For example:

  <div xmlns:ivan="http://ivans-profile" xmlns:mark="http://marks-profile">
    <div about="[ivan:]" rel="foaf:knows" resource="[mark:]" />
    <div about="[mark:]" rel="foaf:knows" resource="[ivan:]" />
  </div>


> 2. If moved along the line of #1 and if we accepted, for a moment, that
> a "prefix:" is a legal CURIE, then the next problem is to define what
> the meaning of "_:" is. Well, there seems to be a perfectly valid answer
> for that: this is a unique identifier chosen by the implementation with
> the restriction that _each_ occurrence of "_:" is a _different_ unique
> identifier. In RDF terms this means that each occurrence of "_:" is a
> _different_ blank node.

It's an interesting idea, but unfortunately, given that the syntax
already works, you might need to find a different way to express your
idea.

In CURIEs the prefix part was meant to be unique but consistent. So it
wasn't that the syntax "_:a" and "_:b" was meant to indicate to a
processor, "please generate bnode a and bnode b"; rather, all a CURIE
processor has to do is to generate some globally unique value, and
place it into the prefix mappings list under the name "_". Then all of
the normal CURIE processing would 'just work'.

I designed it that way so that we could get CURIEs to provide support
for bnodes, without actually talking about bnodes, which seem to me to
be out of scope for a URI abbreviation syntax.

Which means that as things stand, although "_:" is a good idea for
saying "give me a new bnode", in CURIE syntax it would always generate
the same identifier, no matter how many times it was used in a
document. (At least as things stand at the moment.)

Regards,

Mark

[1] <http://www.w3.org/TR/curie/>

-- 
  Mark Birbeck, formsPlayer

  mark.birbeck@formsPlayer.com | +44 (0) 20 7689 9232
  http://www.formsPlayer.com | http://internet-apps.blogspot.com

  standards. innovation.
Received on Sunday, 16 December 2007 17:52:19 GMT

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