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From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 15 Oct 2007 21:01:50 +0100
Message-ID: <4713C72E.3030009@hp.com>
To: Lee Feigenbaum <lee@thefigtrees.net>
Cc: Bijan Parsia <bparsia@cs.man.ac.uk>, 'RDF Data Access Working Group' <public-rdf-dawg@w3.org>

Lee Feigenbaum wrote:
> Bijan Parsia wrote:
> [snip]
>>>> Be that as it may, I as an implementor and a user would find it 
>>>> helpful if there were a note pointing out this aspect. I confess 
>>>> that I would never in this lifetime have come up with that reading. 
>>>> So, if it would be possible to add a bit of text somewhere that 
>>>> clarified this point, I think that'd be swell.
>>> What would it say?
>> "Please note that due to serialization freedom, the serialized results 
>> may contain, syntactically, duplicate triples. There is no way in 
>> SPARQL to force the endpoint to return a syntactically duplicate free 
>> CONSTRUCTed graph."
> Thanks for the suggested text. From my point of view, in the end, this 
> is the editors' decision. As we're wrapping up loose ends, we'll 
> consider it at tomorrow's teleconference. Please feel free to attend if 
> you'd like to speak in favor of including some sort of note. (Either 
> way, we'll cover the issue and make a decision.)
> Personally, I'd quite prefer that the query language draft not begin 
> talking about endpoints right now; it seems way out of scope to me.

Right - it's the protocol spec, if anywhere.  That does with the on-the-wire 

2.1.3 says:

an RDF graph [RDF-Concepts] serialized, for example, in the RDF/XML syntax 
[RDF-Syntax], or an equivalent RDF graph serialization, for SPARQL Query for 
RDF query forms DESCRIBE and CONSTRUCT).
so it refs RDF concepts right after "graph" and there is says

The underlying structure of any expression in RDF is a collection of triples, 
each consisting of a subject, a predicate and an object. A set of such triples 
is called an RDF graph (defined more formally in section 6).

IF anywhere - a note at that point would be possible.  To me (not a protocol 
editor), though,it's just an implementation technique a system has chosen 
because the RDF serializations permit - c.f. HTTP permits compression.

>>> As far as I can see, any confusion about whether to expect duplicates 
>>> or not is really a product of the serialization rather than of the 
>>> query language.
>> I don't see why we can't informatively mention this from the query 
>> language spec. The consequence is that, as implementor, I don't have 
>> to distinct my results before constructing anything. That seems 
>> perfectly relevant in the query document.
> I guess what I don't understand is where you, as an implementor, think 
> the query language spec says that you _do_ have to distinct the results. 
> I guess you're saying that the set-union implies that.
>>> Even the protocol doesn't mandate any particular serialization of an 
>>> RDF graph. If there existed a serialization that prohibited listing 
>>> the same triple twice (are there?), then I'd imagine that it would 
>>> work fine with the protocol as-is.
>> So we can serialize to Turtle? Isn't this a pretty big 
>> interoperability hole?

Turtle does not restrict the serialization to require no duplicates.  Nor 

> I guess it depends what you mean by interoperability hole? In any case, 
> this dates from: http://www.w3.org/2006/01/10-dawg-minutes#item02 (and 
> then 
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2006JanMar/att-0113/12-dawg-minutes.html#item02 
> )
>>> I'm not saying I object to a bit of (informative) text giving a 
>>> heads-up somewhere... I'm just not sure where it would go and what it 
>>> would say.
>> I would put it right after the passage I quoted. I would put some 
>> wordsmithed version of what I wrote above.
> As I said, thanks. Andy and Eric, what do you think?

As above - serialization is the protocol.  The query language does not cover 
the XML results format either.


> Lee
>> Cheers,
>> Bijan.

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Received on Monday, 15 October 2007 20:02:21 UTC

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