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Re: Collection / Grammar Issue

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Thu, 16 May 2013 13:41:29 +0100
Message-ID: <5194D3F9.4060002@epimorphics.com>
To: public-rdf-comments@w3.org


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 { ( ) }

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 12:42:09 UTC

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