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RE: A possible structure of the datatype system for OWL 2 (related to ISSUE-126)

From: Michel_Dumontier <Michel_Dumontier@carleton.ca>
Date: Wed, 9 Jul 2008 12:29:03 -0400
Message-ID: <AB349814F1ECB143A5D4CD29C7A6456902EB31E9@CCSEXB10.CUNET.CARLETON.CA>
To: "OWL Working Group WG" <public-owl-wg@w3.org>

Boris,
  Indeed, from a user's perspective, I would prefer a single datatype. I
find your proposal very reasonable from that perspective. 

Thanks,

-=Michel=-



> -----Original Message-----
> From: Boris Motik [mailto:boris.motik@comlab.ox.ac.uk]
> Sent: July 9, 2008 3:32 AM
> To: 'Michel_Dumontier'; 'OWL Working Group WG'
> Subject: RE: A possible structure of the datatype system for OWL 2
> (related to ISSUE-126)
> 
> Hello,
> 
> This is mainly because that's the way how things work in RDF. In RDF,
you
> have plain literals which can have a language tag or not.
> owl:internationalizedString corresponds to plain literals with a
language
> tag, and xsd:string corresponds to plain literals without
> a language tag.
> 
> I see that this is rather silly from a user's perspective, and there
might
> be a way of unifying things; however, it requires a
> change to the value space of xsd:string. We could have the following
> definitions:
> 
> - The value space of owl:internationalizedString is a set of pairs of
the
> form ("string",langTag), where langTag includes all ISO
> language tags, as well as a special 'null' language tag.
> - The value space of xsd:string is a set of pairs of the form
> (string,'null').
> 
> In this way, we've made xsd:string a subset of
> owl:internationalizedString. Strictly speaking, that is a backwards
> incompatible
> change; however, I don't believe that it is detectable in any way (in
RDF
> or in OWL 1), mainly because in RDF and OWL 1 there was no
> way to refer to the set of all internationalized strings.
> 
> Let me know how everyone feels about this.
> 
> Regards,
> 
> 	Boris
> 
> > -----Original Message-----
> > From: public-owl-wg-request@w3.org
[mailto:public-owl-wg-request@w3.org]
> On Behalf Of
> > Michel_Dumontier
> > Sent: 08 July 2008 19:57
> > To: OWL Working Group WG
> > Subject: RE: A possible structure of the datatype system for OWL 2
> (related to ISSUE-126)
> >
> >
> > Hi Boris,
> >   I'm concerned about the disjoint spaces for xsd:string and
> > owl:internationalizedString. What reasons do you have for the
> > distinction? I view the latter as a specialization of a more generic
> > string datatype. Can we not propose one owl:string that supports
both?
> >
> > Cheers,
> >
> > -=Michel=-
> >
> >
> >
> > > -----Original Message-----
> > > From: public-owl-wg-request@w3.org
> > [mailto:public-owl-wg-request@w3.org]
> > > On Behalf Of Boris Motik
> > > Sent: July 8, 2008 12:16 PM
> > > To: 'OWL Working Group WG'
> > > Subject: A possible structure of the datatype system for OWL 2
> > (related to
> > > ISSUE-126)
> > >
> > >
> > > Hello,
> > >
> > > After a very in-depth discussion about the issues related to
datatypes
> > > (thanks everyone involved!), I thought it would be good to
> > > summarize some of the outcomes of a discussion and to outline a
> > possible
> > > structure of the datatype system. Thus, in this e-mail,
> > > I'll try to (semi-)formally define a datatype map -- the "thing"
that
> > > defines how datatypes would work in OWL 2.
> > >
> > > 1. Datatype Map
> > > ----------------
> > >
> > > A datatype map consists of the following things:
> > >
> > > - a set of datatypes
> > >   - each datatype provides a set of allowed facets
> > > - a possibly infinite set of constants (likely to be renamed to
> > literals,
> > > but I'll stick to "constant" for the moment)
> > >   - each constant consists of a lexicalValue and a typeURI
> > >   - it is written as "lexicalValue"^^typeURI
> > >
> > > Each datatype DT is assigned a value space DT^D, which is just a
> > nonempty
> > > set.
> > >
> > > Each constant c is assigned a value c^D, which is just an object
from
> > the
> > > union of the value spaces of all datatypes.
> > >
> > >
> > > Thus, a datatype can be thought as a class with a predefined
> > extension.
> > > Note that this definition does not assume any relationship
> > > between the set of supported typeURIs (which determine the allowed
> > > constants) and the set of datatypes (which determine the allowed
> > > sets of values).
> > >
> > > 2. Allowed datatypes
> > > ---------------------
> > >
> > > Comformant OWL 2 implementations would be required to support the
> > > following base datatypes, each of whose value spaces would be
> > > disjoint:
> > >
> > > - owl:number - the value space is the set of all real numbers
> > > - xsd:string - the value space is the set of all Unicode strings
in
> > normal
> > > form C
> > > - owl:internationalizedString - the value space set is the set of
> > pairs of
> > > the form (string,langTag)
> > > - xsd:hexBinary - the value space is the set of all finite
sequences
> > of
> > > octets
> > >
> > > The following datatype would also be supported in OWL 2:
> > >
> > > - xsd:integer - the value space is the subset of the value space
of
> > > owl:number containing all integers
> > >
> > > Finally, we might support the following "shortcut" datatypes,
whose
> > value
> > > spaces can be defined from the value spaces of the above
> > > mentioned datatypes using facets
> > >
> > > - various xsd:integer derivatives, such as xsd:int and xsd:long
> > > - various xsd:string derivatives, such as xsd:Name
> > >
> > > 3. Allowed constants
> > > ---------------------
> > >
> > > Conformant OWL 2 implementations are required to support the
following
> > > constant types:
> > >
> > > - "nnn"^^xsd:int and all derivatives that fall within xsd:int -
all
> > such
> > > constants are to be interpreted as elements of owl:number
> > > - "aaEbb"^^xsd:float - all such constants save for NaN and +-inf
are
> > to be
> > > interpreted as elements of owl:number
> > > - "abc"^^xsd:string - interpreted as "abc"
> > > - "abc"@langTag - interpreted as a pair ("abc",langTag)
> > >
> > >
> > > 4. Discussion
> > > --------------
> > >
> > > The set of constants is chosen such that implementations don't
need to
> > > support numbers with arbitrary precision, which might be
> > > quite cumbersome. In fact, implementations are only required to
> > support 32
> > > bit integers and single precision floating point numbers.
> > > There are efficient ways to represent these on virtually all
systems.
> > >
> > > The set of datatypes, however, allows one to refer to the sets of
all
> > > integers and real numbers. This allows one to specify the
> > > ontology in a way that makes reasoning easy.
> > >
> > > Implementations are free to support other constants as well. Note
that
> > > these extensions do not necessarily mean that we need new
> > > datatypes (i.e., new value spaces). For example, an implementation
> > might
> > > choose to support arbitrary precision numbers via constants
> > > of the form "123.03"^^xsd:decimal. Note that the proposed list of
> > > datatypes already contains the appropriate value space for such
> > > constants (i.e., owl:number).
> > >
> > > The open issues are what to do with NaN and +-inf and with
date-time
> > > datatypes.
> > >
> > > Regards,
> > >
> > > 	Boris
> > >
> > >
> >
> 
Received on Wednesday, 9 July 2008 16:29:43 UTC

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