Sandro's proposal VS RDF Datasets

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!

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

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

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.

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

Received on Friday, 27 April 2012 10:02:09 UTC