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Re: [TF-PP] Property Path FPWD

From: Andy Seaborne <andy.seaborne@talis.com>
Date: Mon, 04 Jan 2010 16:53:07 +0000
Message-ID: <4B421CF3.9040205@talis.com>
To: Ivan Herman <ivan@w3.org>
CC: Souripriya Das <SOURIPRIYA.DAS@oracle.com>, Lee Feigenbaum <lee@thefigtrees.net>, Axel Polleres <axel.polleres@deri.org>, W3C SPARQL Working Group <public-rdf-dawg@w3.org>


On 04/01/2010 12:31 PM, Ivan Herman wrote:
> Hi Andy,
>>> - I am not sure what "A path of length zero connects a graph node to
>>> itself." means in terms of a triple pattern...
>>
>> ?x :p* ?y needs a meaning.  :p* can appear in more complex paths
>> (rdf:first*/rdf:rest).
>>
>> Working backwards from e.g. ?list rdf:first*/rdf:rest ?elt, ?list
>> rdf:first* ?x would match with ?x equal to whatever ?list is.
>>
>
> Hm. Alternatively, ?x :p* ?y would not match anything with length zero?

Then ?list rdf:rest* ?elt does not match the beginning cell of a list and

   ?list rdf:rest*/rdf:first ?elt

(which eventually I will write correctly!)

does not find the first element of a list without making :p* different 
from the :p* in :p*/:q

It does have a nice effect that

   :C rdfs:subClassOf ?class

includes :C (as per inference rule that :C rdfs:subClassOf :C).

An app can write "+" to skip the zero match "+" is '1 or more' where "*" 
is 'zero or more'

	Andy
Received on Monday, 4 January 2010 16:53:40 GMT

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