W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > July to September 2006

Re: One semi-historical point (was Re: ISSUE: DISTINCT is underspecified)

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 18 Aug 2006 19:11:49 -0700
Message-Id: <p06230951c10c1fff0e74@[]>
To: Bijan Parsia <bparsia@cs.man.ac.uk>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>On Aug 17, 2006, at 8:34 AM, Pat Hayes wrote:
>>Well, this is an aside to our main discussion here, but I think 
>>that it would be quite acceptable to have an RDF query standard 
>>which was defined *entirely* syntactically, and simply treated an 
>>RDF graph as a triple store, and used essentially algebraic 
>>operations to troll through it for patterns that match and satisfy 
>>superficial conditions (which might include semantic conditions if 
>>those can be computed locally, eg typed literal values). This was 
>>basically the design we had originally, about which so many 
>>protests were received wanting a more 'semantic' account.
>I think is a point of misunderstanding. If y'all said, "We're 
>defining the Query Of RDF Syntax (QORS) language, and if you want to 
>do simple, or rdf, or rdfs, with or without D, or even OWL, well, 
>you're out of luck, make a new standard and you might consider 
>borrowing our query  language syntax" I would not have objected.

But I don't think you *are* out of luck for RDF/S/D. OWL... well yes, 
OWL is more complicated because it has disjunctions in it.

>Or at least not in the same way. I'm fine without a unitary semantic 
>framework per se. Just let me *say* in my own way, what the 
>semantics are (ok, some framework would be nice, just to make them 
>easier to read; but I'm fine with an outlier), and give me good 
>hooks to indicate when I'm using it (and the hooks should be in the 
>query language please; not all sparql query is across the web in any 
>interesting way).
>What I objected to was 1) a syntactic reading that in no way tied to 
>the RDF Semantics document

It was tied to it, in the sense that the subgraph/match design 
corresponds directly to simple entailment. And the entailment lemmas 
then give you at least a spec for RDF and RDFS, if not a very good 
implementation strategy off the cuff, as it were. I agree, the XSD 
case needs more work.

>, and 2) the claim that this would require no change in order to 
>work for simple, rdf, rdfs, and even OWL queries.

I hope nobody made that last claim about OWL. I certainly did not.

>This is manifestly not true. There are people in the working group 
>who support RDFS, and at the very least you have to say something 
>about contradictory documents.

True, but you can follow what the RDF semantics document says, which 
refers to the concept of  'datatype clash'. The point being that 
quite a lot of this was already worked out in the RDF WG and is 
documented (with some known bugs, which are now fixed by others), and 
we *could* have simply directly used this stuff, with minimal change. 
But it wouldn't extend this simply to OWL-DL, indeed.

>Even if you go with maximal consistent subsets, that still needs to 
>be said, explained, etc.

True, true, there is work to be done. But it still would make for a 
much easier basic design (and one which is tied closely to the extant 
implementations) and a much simpler description. Issues of how to 
describe binding restrictions are much simpler when the notion of 
pattern matching is built into the primary definitions, for example.

>So my problem then is the same as my problem now: Lots of things are 
>unspecified or underspecified. Some of the offered ways of 
>specifying just would work very well if at all.
>>>  And I think we should make the semantics available. (Now, of 
>>>course, we're disagreeing on what the semantics require. Let me 
>>>weaken my principle to say that it should help people understand 
>>>the semantics of the graph.)
>>OK, Im quite happy with that reading. But I still think that its 
>>important to not suppress answers which can be used to extract 
>>*semantically* distinct information entailed by the graph. I guess 
>>my point is that it is the semantics of the *graph*, not of the 
>>*answers*, that likely matter most to a querying agent.
>Well, we disagree. Or at least, I think focusing the semantics of 
>the answers are:
>	1) important
>	2) reasonable
>	3) easier to specify, understand, and implement
>This doesn't mean I feel a need to kick yours out, but if there's 
>only one, yeah, this is the one I'll support.

Fair enough that we disagree. However, I stick to my point. IMO, the 
answers are primarily a way to extract information from the graph. 
It's the graph that is being queried.



IHMC		(850)434 8903 or (650)494 3973   home
40 South Alcaniz St.	(850)202 4416   office
Pensacola			(850)202 4440   fax
FL 32502			(850)291 0667    cell
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Saturday, 19 August 2006 02:12:17 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:15:27 GMT