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RE: Model Theory draft + tidiness

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Wed, 30 Jan 2002 12:35:57 -0600
Message-Id: <p05101048b87dea21c1e1@[65.212.118.208]>
To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org
Sorry this reply is late.

>Jeremy:
>>  > Tidiness had already vanished from the latest editors draft of the model
>>  > theory, which is the one I was working from.
>Sergey:
>>  I'm assuming you are referring to
>>
>>
>http://lists.w3.org/Archives/Public/www-archive/2002Jan/att-0007/01-RDF_Mode
>l_Theory.htm
>>
>>  There, in Appendix A, Subsec 1, tidyness is defined in condition 3 for
>>  both urirefs and literals. The comment "graph is tidy on uriref nodes"
>>  should in fact say "... tidy on uriref and literal nodes", since label()
>>  is used both for uri nodes and literal nodes - unless Pat had something
>>  else in mind? Pat, did you?
>
>
>I was referring to that version (dec 14 draft)
>
>Near the beginning it says
>
>"Notice that disjoint graphs do not have any blank nodes in common, by
>definition, and that each separate occurrence of a literal is considered a
>separate node (in contrast to urirefs); we will therefore distinguish
>between literals and literal nodes."
>
>I think there are some editorial issues that have left confusion.
>
>Sergey, wanting tidiness, read tidiness.
>Jeremy, wanting untidiness, read untidiness.
>
>I think the document probably allows both readings.

The latest version of the MT has this paragraph, which I hope will be 
unambiguous:

To describe RDF graphs it is first necessary to define the things
   that can act as nodes and arcs of the graph. There are three kinds of node in
   any RDF graph: urirefs, literal nodes, and blank nodes. A 
<i>uriref</i> is defined
   to be a URI reference in the sense of <a href="#bib_uri">[RFC 
2396]</a>.<span class="newer">We
   do not distinguish between urirefs and uriref nodes because urirefs 
are considered
   to be nodes in themselves</span>. A literal node is a particular 
<i>occurrence</i>
   of a literal; and blank (or unlabeled) nodes are considered to be drawn from
   some set of 'anonymous' entities which have no 'label' and are unique to the
   graph. Finally, every arc in an RDF graph is labelled with a uriref. The same
   uriref may label several arcs and also be a node in the graph. An RDF graph
   can then be defined as a set of triples of the form &lt;S, P, O&gt;, where P
   is a uriref, S is either a uriref or a blank node, and O is either a uriref,
   a blank node, or a literal.  Note that a given uriref may occur in more than
   one graph, but blank nodes and literal nodes are unique to each graph. This
   reflects the fact that urirefs are considered to have a 'global' 
meaning<span class="newer">
   but blank nodes and literals do not: blank nodes because they are 
local to the
   graph, and literals because each occurrence of a literal is considered to be
   unique. (This may be <a href="#litdisclaim">altered in future</a>; at present
   it is the most conservative assumption for the model theory to 
make, since some
   datatyping schemes may assign different interpretations to several 
occurrences
   of the same literal.)</span>

Pat

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Received on Wednesday, 30 January 2002 13:35:38 EST

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