[ENT] Review comments on the SPARQL 1.1. Entailment regime document

Birte, Chime,

I have gone through the document today. I have a bunch of comments; I have cut them into two blocks

- Purely editorial issues. To make things simpler and more manageable, I will send a separate mail listing only those. Many of the comments are a matter of style, and none of those are show stoppers.
- Some issues that merit discussions, see below. Either we should solve them right away, or we should really put editorial comments into the text referring to the fact that, well, these are issues that we will have to solve (if you agree with me on those, that is). This should be done, in my view, before publication. The reason I explicitly added Axel and Sandro here is because some of the issues are RIF related...  

So here we go...

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Editors' note right before section 3: this editor's note was present in the previous draft and we got no comments on that from the community. As far as I know the WG is o.k. with the design choices taken by the document. I therefore wonder whether it is still relevant to keep those editors' notes...

This is true for possibly other editorial notes that did appear in earlier versions.

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Question/comment on Section 6.6.2

I think I would also add some more explanation to the sentence 'Without C2 one would...'.

My understanding is that a pure inference would generate a possible values for ?x going through all possible datatypes with their combination with facets, which would then generate an infinite number of those. But C2 restricts that to those appearing explicitly in the vocabulary. If I am mistaken, that would still include ?x/xsd:date, ?x/xsd:NMTOKEN, etc, right? Ie, this select will return a whole bunch of things...

Is that so? Maybe adding some additional explanation at that point might be useful

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I am lost in Section 6.6.3. In the last part you refer to a query with two variables, ?s and ?d, and I am not sure what query you are talking about...

I presume that the sparql example is simply missing?

I was thinking about SELECT ?s ?x WHERE { ?s ex:dp ?x }...

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Section 7

At the moment, the http://www.w3.org/ns/entailment/ vocabulary does _not_ include the

http://www.w3.org/ns/entailment/RIF-RDF-Strongly-Safe-Core

but only

http://www.w3.org/ns/entailment/RIF

It is easy for me to add this additional URI, but I have to be sure this is o.k. with the RIF group, and whether it is the correct name. And, if I add this, shouldn't I add others? Which ones? Axel, Sandro, can you help on that?

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Section 7.1

I think we have a pending issue as for which namespace rif:imports is in. The current text does not specifies this at all. There should be a namespace document, too.

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Section 7.1

I also have an issue with the way rif:imports is defined. The text says that the _Graph_ should contain the predicate rdf:imports. This means, if my understanding is correct, that I cannot use that in the query, ie, I cannot have a query that says

SELECT *
WHERE {
   [] rdf:imports <...pathtoruleset...>
   ... all kinds of patterns
}

In other words, I cannot dynamically assign rule sets to the dataset. For a user this looks like a serious restriction because that means that the dataset provider dictates the rule sets it has, rather than the user.

Isn't it possible to say that the rdf:imports can also be part of the BGP and has, well, the same semantics of referring to a rule set? 

Actually, the same question applies to various OWL regimes, too. Can I have a [] owl:imports <...> in my BGP? Should we allow this?

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Section 7.1

The text refers to http://www.w3.org/2007/rif-import-profile#Simple but that URI does not seem to exist. Do you mean

http://www.w3.org/ns/entailment/Simple

which is referred to from 

http://www.w3.org/TR/rif-rdf-owl/#Importing_RDF_and_OWL_in_RIF?

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Section 7.2

The rule set example uses

<> rif-rdf:usesRuleset <... path to the above document ...> .

shouldn't that be

rif:imports

instead?

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I wonder whether it would be good adding some additional (informal) text in the RIF related text that makes it clear that, although we define the entailment regime only in terms of the RIF-Simple, it is possible to define RIF Core rule sets that describe RDFS and even OWL-RL. Ie, with suitable rule sets, this entailment is much more powerful than it looks at first. A reference to

http://www.w3.org/TR/2010/WD-rif-owl-rl-20100511/

and to ter Horst's paper (which, actually, still appears in the reference list) would be useful.

That is it...

Ivan

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Ivan Herman, W3C Semantic Web Activity Lead
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