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Re: big issue (2001-09-28#13)

From: Jan Grant <Jan.Grant@bristol.ac.uk>
Date: Mon, 1 Oct 2001 12:22:36 +0100 (BST)
To: Sergey Melnik <melnik@db.stanford.edu>
cc: RDFCore WG <w3c-rdfcore-wg@w3.org>
Message-ID: <Pine.GSO.4.31.0110011220590.20841-100000@mail.ilrt.bris.ac.uk>
I've been thinking along very similar lines. See
http://ioctl.org/rdf/literals
which has a mix of related ideas, some good, some bad, some wrong.
Would paste in the relevant text here (apologies for not doing so) but
very slow line to university at the moment.
jan


On Fri, 28 Sep 2001, Sergey Melnik wrote:

> This is a followup clarification regarding the issue #13 assigned to me
> this Friday (what an inspiring number play) and christened "datatypes".
> At the same time, after giving some context information, I'm throwing
> the ball into the game by putting forth some (hopefully, provocative)
> suggestions.
>
> It seems to be generally acknowledged that the following 4 issues are
> closely related and, thus, may need to be resolved simultaneously:
>
> 1. Are literals resources?
>
>   Tracked as: #rdfms-literals-as-resources
>   Dependent issue: #rdfms-literalsubjects, would be resolved immediately
> if literals are resources
>
> 2. Are resource URIs opaque or composed of namespace + local name?
>
>   Tracked as: #rdfms-uri-substructure
>   Intro:
> http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Jul/0270.html
>
> 3. Are literals opaque or composed of unicode string + language ID/URI?
>
>   Tracked as: #rdfms-xmllang
>   Related: #rdfms-literal-is-xml-structure
>   Summary:
> http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Jul/0122.html
>            (suggests literals are composite values)
>
> 4. How to use datatypes in RDF?
>
>   Tracked as: #rdfs-xml-schema-datatypes
>   Possible foundation: http://www.w3.org/TR/xmlschema-2/
>
>
> Let me start the discussion backwards. What are the requirements for
> using datatypes? Here is a quote from
> http://www.w3.org/TR/xmlschema-2/#requirements:
>
> - provide for primitive data typing, including byte, date, integer,
> sequence,
>   SQL and Java primitive datatypes, etc.;
> - define a type system that is adequate for import/export from database
> systems
>   (e.g., relational, object, OLAP);
> - distinguish requirements relating to lexical data representation vs.
>   those governing an underlying information set;
> - allow creation of user-defined datatypes, such as datatypes that are
> derived
>   from existing datatypes and which may constrain certain of its
> properties
>   (e.g., range, precision, length, format).
>
> In other words, to use datatypes effectively, we must at least be able
> to:
>
> a) identify a resource (or literal) as a typed one
> b) refer to a datatype as a resource (this allows defining datatypes,
> determining their equivalence etc.)
>
> Here is a tentative suggestion of how datatypes may be introduced into
> RDF. This is also an attempt of a simultaneous attack on issues 1-4
> above. Previously, I proposed several ways of treating literals as
> resources. For a change, here is an alternative view:
>
> s1) A resource is a pair of (URI, local name) (URIs may contain "#"
> etc.; this satisfies the M&S requirement that given a property, one can
> retrieve the schema describing this property)
>
> s2) A literal is a pair <resource, unicode string>. The first component
> of a literal denotes its (data)type.
>
> That's it for now. Here is an example of how (s1),(s2) address (a),(b):
>
> Notice that the datatypes themselves are resources. For instance, a
> resource for "integer" defined in XML schema is
> (http://www.w3.org/2001/XMLSchema-datatypes, integer). Literals are
> tagged using resources. For instance, value "5" is tagged as "integer"
> using <(http://www.w3.org/2001/XMLSchema-datatypes, integer), "5">. The
> definition of the datatype of the above primitive value "5" can be
> retrieved from http://www.w3.org/2001/XMLSchema-datatypes (according to
> M&S requirement).
>
> These are the (possible) consequences:
>
> c1) Resources and literals are disjoint
> c2) Language tagging in literals is done using the typing mechanism,
> e.g.
>     <(http://iso.org/lang/, en-us), "rat">
> c3) #rdfms-literalsubjects is still open.
> c4) s1,s2 say nothing about the type system or creation of user-defined
> types. XML schema introduces a very elaborate one (maybe ugly, but
> comprehensive), which may or may not be worth mirroring in RDF.
>
> Rotten tomatoes are welcome.
>
> Sergey
>
>

-- 
jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/
Tel +44(0)117 9287088 Fax +44 (0)117 9287112 RFC822 jan.grant@bris.ac.uk
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Received on Monday, 1 October 2001 07:25:37 EDT

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