Re: ISSUE-30: How does SPARQL's notion of RDF dataset relate our notion of multiple graphs?

Pat, Richard, group...

On Apr 19, 2011, at 06:32 , Pat Hayes wrote:
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> 
> The mathematical notation doesn't imbue anything.  (I did my damndest to avoid mathematical notation when writing the RDF document, by the way: some of my colleagues were horrified by the lack of greek letters.) The actual mathematics (not the notation) imbues only a useful degree of precision. (This mathematics really is pretty simple: sets and mappings, one level deep. If someone can't follow that, then they probably cannot understand RDF itself. The XML schema specs are *way* more complicated than the entire RDF spec document suite.

That is correct. Praise to you: I can read the RDF Semantics document (ok, it took me some time at first read, but not that much) but I never succeeded in really grasping the XML Schema semantics document. That being said, in view of the relatively low acceptance of XML Schemas (compared to other Schema languages) this may not be the best example:-)

> Can you tell me what a 'facet' is in one tweet?)  And the 'magic' is only that it deals directly with the central idea of truth. I will claim that any semantic account that is worth having must somehow do this, and that without this the notation really is meaningless. To publish some data in RDF is to *claim that the RDF is true*. If the spec does not say what this claim means, then yes, publication of RDF is meaningless. 
> 
> Now, in order to avoid starting a philosophical war, I would agree that we need to find ways to convey the essence of RDF to a wider audience. If model-theoretic ideas really are as hard to grasp as you claim, then perhaps we can find some other way to present the ideas to that audience. But I still think that we need to have a model theory as a normative reference. It is just too useful to do without. The pedagogic task needs to be kept distinct from the foundational role of a truth-based semantics. 

I must say that, for me, this is the essence of the matter. As I said above, I do not have any problem with the Semantics document, even if it is a difficult read here and there and I probably miss some niceties. It is, in fact, almost the only document I regularly go back to of the whole 2004 set... But: we have to recognize that this document is pretty much unreadable to many people, primarily to those who do not have a rigorous mathematical study as part of their personal history.

When making tutorials and such, I always use the (informative) entailment rules. I found that any decent computer programmer understands those because they can bind it to a traditional program; I never mention model theory. I know it is informative, and I know that blindly applying those rules may not be the best approach in an implementation (and Pat you listed a bunch of implementation strategies) but those issues are only relevant to the (few) implementers in the community and not to the (majority) RDF users. And the problem is that the entailement rules in the current document are a bit hidden, almost as an appendix, and are also marked informative.

Maybe what we would have to have are two documents. One is for RDF users: include the RDF(S) vocabularies, notion of graphs, etc, etc, and the entailment rules: this is how these terms are used. Making it clear that those rules are the way they are as a result of the niceties of the underlying mathematics. And that mathematics (ie, the model theory) is then the subject of a separate document, which may also be relevant to implementers but not for the general public.

I am sure the devil is in the details but I believe we would greatly improve the acceptance of RDF(S) by doing so. 

Ivan 


> 
> Pat
> 
>> 
>> Best,
>> Richard
> 
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Ivan Herman, W3C Semantic Web Activity Lead
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