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Re: first and rdf:rest as functional property

From: Reto Bachmann-Gmür <reto.bachmann@trialox.org>
Date: Mon, 23 Mar 2009 12:43:13 +0100
Message-ID: <49C775D1.8020406@trialox.org>
To: Jeremy Carroll <jeremy@topquadrant.com>, 'Michael Schneider' <schneid@fzi.de>, 'Bijan Parsia' <bparsia@cs.man.ac.uk>, Pat Hayes <phayes@ihmc.us>, Story Henry <henry.story@bblfish.net>
CC: 'Semantic Web' <semantic-web@w3.org>
Thank you all for your contributions to these thread. I'll try to
summarize how I understood things with regards to the original questions:

> My questions:
> - Are there useful usages where an rdf:list has several distinct
> rdf:first and rdf:rest value?
>   
RDF Semantics speaks about "well-formed" list to refer to lists for
which the above (and possibly other) conditions are true. RDF however
does not impose "well-formedness" so it would be possible write
'surprising', 'elegant', 'creative', 'unconventional', 'imaginative' or
'beautiful' lists that do not match the condition. However it explicitly
mentions that extensions may exclude lists that violate the convention
so that creating beautiful non-regular lists is an interoperability bug.


> - Is it just not written that rdf:first and rdf:rest are functional
> (maybe due to some spec layering reasons) or is false to consider
> rdf:first and rdf:next as functional?
There's currently no specification asserting that they are, but as RDF
semantics explicitly allows well-formedness limitations in semantic
extension there statements are not false (as this would contradict  the
semantic extensions).


To me this situation this situation is not really satisfactory.  Asserting:
|
_:666 rdf:first <ex:aaa> .
_:666 rdf:first <ex:bbb> .
_:666 rdf:rest rdf:nil .
<ex:aaa> ||owl:differentFrom <ex:bbb>

|would be an interoperability bug as it would be a contradiction with
possible semantic extensions while on the other hand we do not currently
have spec legitimation to draw the following conclusion:

|_:666 rdf:first <ex:aaa> .
_:666 rdf:first <ex:bbb> .
_:666 rdf:rest rdf:nil .
=>
<ex:aaa> ||owl:sameAs <ex:bbb>|

Even if asserting functionality of rdf:first and rdf:rest doens't rule
out all usage of the properties that result in non standard lists, it
would in my opinion be a benefit for the interoperability of different
system if these statements would be asserted by semantic web standards.
Any chance that a semantic extension as foreseen by RDF Semantics
becomes part of the semantic web specifications?

Cheers,
Reto
Received on Monday, 23 March 2009 11:44:13 GMT

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