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Re: Every CONSTRUCT is DISTINCT?

From: Lee Feigenbaum <lee@thefigtrees.net>
Date: Mon, 15 Oct 2007 15:24:07 -0400
Message-ID: <4713BE57.4030808@thefigtrees.net>
To: Bijan Parsia <bparsia@cs.man.ac.uk>
CC: 'RDF Data Access Working Group' <public-rdf-dawg@w3.org>

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.

>> 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?

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?

Lee

> Cheers,
> Bijan.
> 
> 
Received on Monday, 15 October 2007 19:24:24 GMT

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