[LC response] To C. M. Sperberg-McQueen

Dear C. M., 

Thank you for your comment 
on the OWL 2 Web Ontology Language last call drafts. 

Point (1): # at the end of namespaces 

Please note that neither OWL 2 nor rdt:text uses XML namespaces. The XML
Namespaces specification uses QNames, which are pairs of the form
(namespace,localName). Thus, when one writes <a:B>, one actually says that the
element's name is a pair whose first element is the URI associated with a, and
whose second element is B. 

RDF (and consequently OWL as well), however, works only with URIs. That is,
resources on the Web are not QNames (i.e., they are not pairs), but are URIs
(i.e., strings of characters). Now RDF/XML says that, when you write <a:B>, you
should generate the URI by concatenating the namespace associated with a with B.
Thus, the RDF suggests that it is using the XML Namespaces specification for URI
abbreviation; however, it is actually using its own mechanism based on
concatenation. This mechanism has later been sanctioned in the CURIE

Because of all that, we are not using the term "namespace" anywhere in either
OWL 2 or rdf:text when we speak about datatype identifiers. Instead, we speak of
prefix URIs, which seem like namespaces, and of prefix names, which seem like
local names. Consequently, to obtain a proper URI after the prefix URI is
concatenated with the prefix name, you need to terminate the prefix URI with #.
After all this, you do get a proper URI that matches Section 3 of XML Schema
Datatypes 1.1 (see [1]). 

Your comment has, however, brought to our attention that XQuery functions are
identified by QNames, rather than URIs. We have therefore changed the
specification to reflect this. The link below summarizes the changes we have


Point (2): Should XSD 1.1 refer to rdf:text? 

We do not believe that XSD 1.1 needs to worry about rdf:text. The main
motivation behind rdf:text was to provide adequate names for the corresponding
sets of plain literals of RDF (we will elaborate more on this below). Thus, the
rdf:text specification is RDF-centric and should not concern much the general
XML datatype architecture. So, while we do not really have objections to you
suggesting a reference from the XML Schema WG, we do not see any need to include
or further tie rdf:text with XSD 1.1. 

Point (3): Required export to plain literals 

First of all, let us note that we lifted this restriction, by changing the MUST
to a SHOULD. We decided that it id better if the equivalence between rdf:text
and plain literals only is relevant for D-entailment, so RDF tools which only do
simple entailment could ignore rdf:text. Still we recommend export to plain
literals. The main goal of rdf:text is to provide names for the set of literals
you already have, not to introduce new types of literals. As the document's
introduction states, names for various sets of literals are often needed in OWL
and RIF (and to some extent in RDFS as well) if you want, for example, to place
appropriate range restrictions on data properties. Consequently, an OWL and RIF
tool vendor will need to support rdf:text. We cannot see how the RDF export
recommendation might dissuade the vendor from supporting rdf:text: with or
without the export restriction, the tool vendor is not gaining any additional

Point (4): rtfn:length function 

The definition says "the number of characters", and we cannot see how this could
be misunderstood. Note that we never talk about various UNICODE encodings, such
as UTF-8, and doing so at this place might come a bit out of the blue. 

Point (5): Internationalization issues 

We agree that these might be important issues; however, they clearly exceed the
scope of rdf:text. The main goal of this specification was to provide adequate
names for the sets of plain literals in RDF, and not to solve all
internationalization problems one might have. 

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Boris Motik
on behalf of the W3C OWL Working Group

Received on Wednesday, 6 May 2009 13:17:04 UTC