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Re: Sandro's proposal VS RDF Datasets

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 28 Apr 2012 20:25:35 -0500
Cc: RDF WG <public-rdf-wg@w3.org>
Message-Id: <57645B94-CD30-4F31-B682-63CFA61B8AA6@ihmc.us>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>

On Apr 27, 2012, at 5:01 AM, Antoine Zimmermann wrote:

> Hi all,
> Now I understand better what Sandro's aiming at. Maybe it was made clear and explicit in previous emails but I have not followed all the discussions on the graph designs. I'll try to make explicit here something that I found unsaid.
> I'll use the phrase "Sandro's view" to denote what *I* think is Sandro's view, which may not be exactly *his* true view. Please forget me if I completetly misunderstood your view, Sandro, and correct me.
> In Sandro's view, TriG files are a way for people to assert things and to include quotes of what other people assert. So a TriG file is always the expression of the opinion/belief/knowledge of the author of the file (note that the author may be any kind of agents, not necessarily a person, let's call it the "implicit author"). So the questions in Sandro's questionnaire really make sense to me now:
> "The default graph is asserted" which means, the implicit author asserts these things that are said in the default graph. And it's also clear why it says that the TriG file entails the Turtle file, as Turtle is another way of asserting things.
> "Named graphs are not asserted" means that the implicit author is not saying those things, just merely quoting them.
> And of course, if you quote something, you do not want to entail anything from it as the quote is the quote. And of course too, if one says "<g> says {:s :p :o . :a :b :c}" you can as well say that "<g> says {:s :p :o}" as any subpart of the quote is also something quoted.
> Now, there is a problem here. It is not the way RDF datasets are supposed to work. It is not the way people in the semantic community use RDF datasets, not even TriG files, as far as I can see.
> TriG documents are not published online. They are used either to serialise an RDF dataset or as configuration files in various tools or simply to partition the triples in a convenient way.
> Let us make a comparison. In Sandro's view, I'd say that a TriG file corresponds to a single book which could refer to many other books. It could be a catalogue which cite, reference, quote, and review other books. Of course, the "named books" inside this book are not "asserted".
> But in SPARQL, an RDF Dataset is like a library. It contains many books that do not necessary reference or quote or cote the other books. It probably has an index (the "default book"). But it does not make sense to say that the statements in those books "are not asserted". All books have their own asserted statements from which you can draw conclusions. E.g., "Luc Skywalker is carrying a light saber" is asserted inside the book, and inside this book, one can entail that "Luc is carrying weight". This does not have an impact on what is asserted in a book of Physics. The book of physics has its own truth from which one can make other entailments. This is what an RDF Dataset is: a library of RDF graphs, each having their own assertions and each carrying implicitly their own conclusions.
> In Sandro's view, there is this idea that:
> <g> { <some triples }
> is asserting something about the relationship of <g> with the triples. But in RDF Dataset, this is just a way to put the triples on a shelf, and the shelf happens to have an identifier. When we put something on a shelf in a library, we do not think that we are asserting a relationship between the shelf and what's on it!

But if you TELL someone that the book is on the shelf, or answer a question about what book is on the shelf, or tell someone WHICH book is on the shelf, then you do exactly assert such a relationship. You did yourself in this very sentence: you said it was ON it. That is a relationship. 

Seems to me that this analogy strongly supports Sandro's notion of graph names as being, well, names of graphs. 

But we can take your view, as I understand it. It is simply a rejection of the very idea of datasets having any normative semantics or meaning. They are just handy datastructures for doing various things with pieces of RDF. Which is fine, and saves us a lot of WG effort, but hasnt really advanced the state of the art very far, and may not really be living up to our charter. 

> In my opinion, if one just want to quote a graph and talk about it, one just needs RDF triples.

No, that won't do. At the very least we need reification or some kind of graph literal construction.

> <g>  a  :Graph ;
>     dc:creator  <me> ;
>     :saysInTurtle  ":s  :p  :o" .

Is ":s :p :o" a string? 

> You can even have a "partial semantics" by separating the triples:
> <g>  :saysInTurtle  ":s :p :o", ":a :b :c" .
> Then it's just a matter of social consensus that :saysInTurtle is used to relate an RDF graph to a Turtle serialisation of that graph. You could also add something to the formal semantics, but on the one hand it would create headachs to all implementers (imposing something to be interpreted as an RDF Graph is much more troublesome than implementing rdf:XMLLiteral, for instance), and on the other hand, I can't think of any concrete real life situation where it's actually useful.

I can. If someone wants to get ambitious with their library and use some OWL reasoning (as for example the BBC are doing, for one) then you really do want to have some connection with the OWL content at the level of model theory, if only to clarify what owl:sameAs is supposed to mean.


> -- 
> Antoine Zimmermann
> ISCOD / LSTI - Institut Henri Fayol
> École Nationale Supérieure des Mines de Saint-Étienne
> 158 cours Fauriel
> 42023 Saint-Étienne Cedex 2
> France
> Tél:+33(0)4 77 42 83 36
> Fax:+33(0)4 77 42 66 66
> http://zimmer.aprilfoolsreview.com/

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Received on Sunday, 29 April 2012 01:26:11 UTC

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