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Value space of CURIE datatype

From: Pete Johnston <Pete.Johnston@eduserv.org.uk>
Date: Tue, 13 Mar 2007 15:05:28 -0000
Message-ID: <5639156310BCBA459673B0D709D28C0F2CB3EF@eduwbl01.edu2000.com>
To: <www-html@w3.org>

Hi,

Thanks to the authors/editors for the work on the CURIE Syntax 1.0
document [1]. I have one question/comment.

The definition of "datatype" in XML Schema Part 2: Datatypes [2] says:

[Definition:]  In this specification, a datatype is a 3-tuple,
consisting of a) a set of distinct values, called its *value space*, b)
a set of lexical representations, called its *lexical space*, and c) a
set of *facet*s that characterize properties of the *value space*,
individual values or lexical items.

And all the datatypes defined by the XML Schema Part 2 document are
defined in those terms.

So my questtion is: what is the value space for the CURIE datatype? 

As far as I can see, the current draft does not specify the value space
for the CURIE datatype - though there are "hints" in the text that seem
to offer two (mutually exclusive, I think?) possibilities:

Option 1: the value space for CURIE is the set of URIs (or IRIs?)

This interpretation might be supported by the fact that e.g. the
introduction says:

> This specification addresses the problem by creating a new data type
whose purpose is specifically to allow for the abbreviation of URIs in
exactly this way.

Also section 4 says:

> In all cases a parsed CURIE will produce a IRI.

However, if the value space is the set of IRIs, then I think the
assertion in section 4 that QNames are a subset of CURIEs is incorrect.
According to XML Schema Part 2, the QName datatype is defined as [3]:

[Definition:]   QName represents XML qualified names. The *value space*
of QName is the set of tuples {namespace name, local part}, where
namespace name is an anyURI and local part is an NCName. The *lexical
space* of QName is the set of strings that *match* the QName production
of [Namespaces in XML].

If the value space of CURIE is the set of IRIs, while it's true that the
lexical space of QName is a subset of the lexical space of CURIE, then,
given the differences in the value spaces, I don't think it's correct to
say that QNames are a subset of CURIEs.

Option 2: the value space for CURIE is a set of tuples {IRI, ifragment}

This interpretation might be supported by the fact that e.g. the
introduction says:

> This type is called a "CURIE" or a "Compact URI", and QNames are a
subset of this.

Also section 4 says:

> CURIEs can be used in exactly the same way that QNames are, with the
modification that the format of the strings before and after the colon
are looser.

However, if the value space of CURIE is this set of tuples, then I think
the document needs to be clearer that the interpretation of this tuple
as a single URI or IRI (by concatenation of the two components of the
tuple) is _not_ a characteristic of the datatype itself, but a choice of
some other specification in which the CURIE datatype is deployed
(similarly, for example, to the case for the interpretation of _some_
QNames in RDF/XML). And so I think it is probably inaccurate to say "In
all cases a parsed CURIE will produce a IRI."; that is true only if some
specification other than the CURIE datatype specification licences that
further mapping of the tuple to an IRI by concatenation.

I had a (very brief) exchange with Mark about this on the
public-rdf-in-xhtml-tf list a while back, and, TBH, I should probably
have pursued the question a bit harder back then! I think Mark's reply
to me [4] was confirming that the value space of CURIE was a set of
tuples, not a set of URIs/IRIs i.e. Option 2 above.

I guess my point is that whatever the value space of the CURIE datatype
is, the document which describes/defines it should be clear about what
that value space is, and (to me) the current draft still seems slightly
ambiguous on this point.

(I say this as someone who is interested in making use of CURIEs, I
should add!)

Cheers

Pete

[1] http://www.w3.org/TR/2007/WD-curie-20070307/
[2] http://www.w3.org/TR/xmlschema-2/#datatype
[3] http://www.w3.org/TR/xmlschema-2/#QName
[4]
http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2005Nov/0013.
html

---
Pete Johnston
Technical Researcher, Eduserv Foundation
Web: http://www.eduserv.org.uk/foundation/people/petejohnston/
Weblog: http://efoundations.typepad.com/efoundations/
Email: pete.johnston@eduserv.org.uk 
Tel: +44 (0)1225 474323
Received on Tuesday, 13 March 2007 15:56:05 GMT

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