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Re: RDF Semantics: use of functions IEXT / ICEXT

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 24 Feb 2003 21:42:01 -0600
Message-Id: <p05111b5fba808ff7b152@[10.0.100.86]>
To: herman.ter.horst@philips.com
Cc: www-rdf-comments@w3.org

>RDF Semantics document,
>last call version, 23 january 2003
>These comments were mailed earlier to the WebOnt WG [1].

This response extends and corrects my earlier reply.

>A consequence of the (new) setup of the RDF semantics
>is that for each occurrence of IEXT(x) or ICEXT(x), it
>should be clear that x is in the domain of the function
>involved.  (For IEXT, this domain is the set IP.
>For ICEXT, the domain is the set IC; compare my
>other comment on this to rdf-comments [2].)
>For example, in Section 3.3 the semantic conditions on
>subClassOf and subPropertyOf take care of this explicitly.
>It seems that this point is not taken care of completely
>consistently throughout the document.

After checking the various cases, I believe that the semantic 
conditions as stated completely define all the relevant domains and 
ranges.

>
>In Section 3.1, RDF interpretations,
>in the table defining an rdf-interpretation, IEXT(I(rdf:type))
>is used before it is clear that I(rdf:type) is in the
>domain of this function (i.e., the set IP).
>Switching the first two lines of this table would remedy this.

Done.

>
>Similarly, it seems appropriate to move the semantic
>conditions on IC and IP in Section 3.3:
>>  IC contains ...[many items]
>>  IP contains ...[many items]
>to become the first conditions, as each of the other
>conditions in this table actually uses one or more of these
>conditions.

Done. For the record, I do not regard the order of these items as 
significant or meaningful.

>
>The semantic conditions on rdfs:range and rdfs:domain in Section 3.3
>do not yet incorporate explicit domain assumptions as just
>discussed.  It seems that additions such as the following need
>therefore to be made:

The additions suggested are not required, since they follow from the 
axiomatic triples in the next table and the other conditions on range 
and domain.

It is probably easiest to express the reasoning in terms of triples 
that must be satisfied by an interpretation I. For example, suppose 
<x,y> is in IEXT(I(rdfs:range)), ie that

I |= (x) rdfs:range (y)
Now, since
I |=  rdfs:range rdfs:domain rdf:Property .  (axiomatic triple)
  it follows by the semantic condition on rdfs:domain that
I |= x rdf:type rdf:Property .
ie, by the basic condition on IP, that x is in IP.

Similar reasoning using a different axiomatic triple shows that y 
must be in IC.


Pat

>
>If <x,y> is in IEXT(I(rdfs:range))
>[then x is in IP and y is in IC] and
>[if, in addition,] <u,v> is in IEXT(x) then
>v is in ICEXT(y)
>
>If <x,y> is in IEXT(I(rdfs:domain))
>[then x is in IP and y is in IC] and
>[if, in addition,] <u,v> is in IEXT(x) then
>u is in ICEXT(y)
>
>The last call versions of these statements (i.e., this text
>without the [...]-additions) seem to be
>remnants from the April 2002 version of the RDF MT, where
>IEXT as well as ICEXT had all of IR as their domain.
>
>Herman ter Horst
>Philips Research
>
>[1] http://lists.w3.org/Archives/Public/www-webont-wg/2003Feb/0067.html
>[2] http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0348.html


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Received on Tuesday, 25 February 2003 10:35:12 GMT

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