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Re: Collection / Grammar Issue

From: Richard Cyganiak <richard@cyganiak.de>
Date: Thu, 16 May 2013 13:55:57 +0100
Message-Id: <07E91A0B-D479-47AC-A743-D6D1C884EE78@cyganiak.de>
Cc: "public-rdf-comments@w3.org" <public-rdf-comments@w3.org>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
On 16 May 2013, at 13:41, Andy Seaborne <andy.seaborne@epimorphics.com> wrote:
> On 16/05/13 10:24, Richard Cyganiak wrote:
> 
>> For the record, I believe this limitation in the grammar is there
>> because the Turtle grammar was derived from the SPARQL grammar, and
>> SPARQL doesn't support such “naked lists” in triple patterns, because in
>> a query they really wouldn't make sense.
> 
> (Another unofficial reply)
> 
> SPARQL does allow just lists:
> 
> ASK { ( 1 ?var 3 4 ) }
> 
> but does not allow:
> 
> ASK { ( ) }

Ok, thanks Andy, I misremembered.

Richard



> 
> To make this work (SPARQL 1.0), there is a certain amount of jumping through hoops.  It makes the treatment of argument lists in function have to have special grammar rules for ().
> 
>    Andy
> 
> Unofficial:
> http://www.sparql.org/query-validator.html
> 
> (does W3C want to take this and support it c.f. http://www.w3.org/RDF/Validator/)
> 
>> I don't see this limitation in Turtle as a big problem, because there
>> are workarounds such as spelling out the list in rdf:first and rdf:rest
>> triples. So just changing the example is fine with me. Adding a note
>> about it might be appropriate.
>> 
>> Richard
>> 
>> 
>> 
>>> How would you use that?
>>> 
>>>        -- Sandro
>>> 
>>>> The production for triples in section 6.5 is:
>>>> 
>>>> [6]triples::=subject predicateObjectList | blankNodePropertyList
>>>> predicateObjectList?
>>>> [7]predicateObjectList::=verb objectList (';' (verb objectList)?)*
>>>> [10]subject::=iri | BlankNode | collection
>>>> 
>>>> According to these productions, the example is invalid.  The subject
>>>> reduces to the collection and must be followed by a verb.  Yet, the
>>>> example does not have a following predicate object list.
>>>> 
>>>> If this is truly suppose to be valid, I think the productions need to be:
>>>> 
>>>>   triples::=subject predicateObjectList |
>>>>                        collection predicateObjectList? |
>>>>                        blankNodePropertyList predicateObjectList?
>>>>   subject ::= iri | BlankNode
>>>> 
>>>> BTW, it would be a wonderful editorial change to number the examples.
>>>> 
>>>> [1] http://www.w3.org/TR/2013/CR-turtle-20130219/
>>>> 
>>>> --
>>>> --Alex Milowski
>>>> "The excellence of grammar as a guide is proportional to the paucity
>>>> of the
>>>> inflexions, i.e. to the degree of analysis effected by the language
>>>> considered."
>>>> 
>>>> Bertrand Russell in a footnote of Principles of Mathematics
>>> 
> 
Received on Thursday, 16 May 2013 12:56:19 UTC

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