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Re: Time-sensitive resources using RDF?

From: Frank Manola <fmanola@acm.org>
Date: Tue, 21 Dec 2004 09:30:25 -0500
Message-ID: <41C83380.8020903@acm.org>
To: neil@oilit.com
CC: www-rdf-interest@w3.org

It's perhaps worthwhile pointing out that RDF provides facilities for 
dealing with datatypes and units of measure.  There is material in the 
RDF Primer on this subject, specifically Section 2.4 on Typed Literals 
(which captures the computing type part), and Section 4.4 on rdf:value 
(which discusses how to introduce units).  Example 21 from that section 
illustrates the general idea, using XML Schema datatypes and a madeup 
vocabulary for the units:

<?xml version="1.0"?>
<!DOCTYPE rdf:RDF [<!ENTITY xsd "http://www.w3.org/2001/XMLSchema#">]>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
          xmlns:exterms="http://www.example.org/terms/">

<rdf:Description
   rdf:about="http://www.example.com/2002/04/products#item10245">
     <exterms:weight rdf:parseType="Resource">
        <rdf:value rdf:datatype="&xsd;decimal">2.4</rdf:value>
        <exterms:units
             rdf:resource="http://www.example.org/units/kilograms"/>
     </exterms:weight>
</rdf:Description>

</rdf:RDF>

Other approaches are also possible, but in an open environment like the 
Web, we are, as Neil suggests, generally going to have to be more 
explicit about describing data.

--Frank

Neil McNaughton wrote:
>  
> 
> A bit of a hobbyhorse I’m afraid, but if you are getting into time 
> sensitive resources, this is data, not text. It therefore behooves the 
> writer of the spec to do something about metadata for the data – in 
> particular, units of measure. I couldn’t get onto the grid.ucy.ac.cy 
> schema to see if it said anything interesting. But when I see <b> 
> 125Mbits </b>, I am led to believe that the data is not being treated 
> rigorously. One would have expected a value – with (perhaps) its 
> (computing) type specified through a reference to a publicly available 
> schema – and (definitely) its units of measure – in a similar way.
>  
> Making this up with an rdf-esque pseudo code (I don’t really speak the 
> lingo…)
>  
>>             <rdf:Seq>
>>                    <b>
>                         <type_namespace>www.ieee.org/definitivedatatypes.xml> 
>                         <data_namespace>www.iso.org/definitiveunitsofmeasure.xml> 
>                         <value_type>IEE_longint</value_type> 
>                         <value-uom>ISO_bps</value_uom> 
>                         <value>125000000</value>
> 
>  And so on
> 
>>             </rdf:Seq>
> 
>  
> 
> Before you look them up – the IEEE and ISO urls are fictitious – 
> although similar may exist unbeknownst to me. 
> 
> The RDF community is seeking rigor for textual relationships but seems 
> to abandon this when a data element comes along… If rdf is to be used 
> for machine reasoning (as opposed to an alternative to local flavors of 
> xml – or even text-described data) then it seems to me that the above is 
> a necessary requirement. Or maybe I have misunderstood something…
> 
Received on Tuesday, 21 December 2004 14:25:30 GMT

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