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Re: [Graphs] Proposal: RDF Datasets

From: Richard Cyganiak <richard@cyganiak.de>
Date: Sat, 27 Aug 2011 17:39:10 +0100
Cc: antoine.zimmermann@insa-lyon.fr, public-rdf-wg@w3.org
Message-Id: <AD213BCA-ADDD-4B62-AE65-5C9B820F1480@cyganiak.de>
To: Ivan Herman <ivan@w3.org>
On 27 Aug 2011, at 06:39, Ivan Herman wrote:
> http://www.w3.org/2009/07/NamedGraph.html

You could have told us about that earlier Ivan!

/me prints a copy

Best,
Richard



> 
> On Aug 26, 2011, at 18:39 , Antoine Zimmermann wrote:
> 
>> Pierre-Antoine,
>> 
>> 
>> I am in total agreement with what Richard says below. However, I sympathise to some extent with your idea. I would be interested to see some people define a datatype for serialised graphs, say in Turtle. Then, they should brainstorm a few use cases and implement some tools around this proposal and see how things are going, gather experiences and come back in a few year with a report and possibly a proposal for standardisation.
>> 
>> Start by defining a datatype for Turtle graph literals:
>> - lexical space is the set of valid Turtle documents;
>> - value space is the set of RDF graphs;
>> - L2V is the mapping from Turtle to RDF graph, as defined in th Turtle spec.
>> 
>> Of course, you can do the same for other syntaxes, but I think Turtle best fits.
>> 
>> Then you may need to introduce a set of terms like rdf:Graph, rdf:serialisation, etc... This set of terms should be crafted in function of the experience that the group gather by trying to deal with their use cases.
>> 
>> BUT, this is certainly not something that should be done within this working group.
>> 
> 
> A few years ago I had an attempt to do something like that
> 
> http://www.w3.org/2009/07/NamedGraph.html
> 
> but then, somehow, I did not _really_ finish it and I am sure it is full of rubbish, too, mainly on the semantics side. But my basic approach in terms of the serialization of this stuff was much more restrictive than Pierre-Antoine's, namely that within a specific serialization one can use only the same serialization for a graph. I indeed do not see why one would allow to use, say, RDF/XML to encode a graph literal when one is in Turtle...
> 
> Although the document is there, I am _not_ sure this is something this WG has to really take up. This is still open in my mind.
> 
> Ivan
> 
>> 
>> AZ.
>> 
>> Le 22/08/2011 18:54, Richard Cyganiak a écrit :
>>> Pierre-Antoine,
>>> 
>>> Thanks for picking this up again.
>>> 
>>> There are several things I don't like about [2].
>>> 
>>> 1. It is not an abstract syntax. It is a mix of concrete and abstract
>>> syntax. Thus it negates the benefits of having an abstract syntax in
>>> the first place. For example, one cannot really describe any
>>> operations over such a multigraph representation without appealing to
>>> the use of various syntax parsers. And one has to explain what
>>> happens if the serialized graph isn't valid in the respective syntax.
>>> Etc
>>> 
>>> 2. It doesn't achieve the goal of standardisation. Different existing
>>> multigraph approaches (TriG, SPARQL, etc) would all look differently
>>> when expressed according to this proposal. Thus, it doesn't promote
>>> interoperability and doesn't actually make working with multiple
>>> graphs any easier.
>>> 
>>> 3. I feel that it is actually more complex than the RDF Dataset
>>> proposal [1] because it requires the definition of one predicate for
>>> every RDF graph serialization, as well as additional vocabulary for
>>> every multigraph representation.
>>> 
>>> 4. It is clear that actually storing or serializing anything in that
>>> way would be a bad idea. Instead, one wants to use optimized syntaxes
>>> that can serialize the graph literals without “double serialization”,
>>> and optimized storage schemes that can actually store and index the
>>> parsed form of the graph literals. But if that is the case, then why
>>> not define an abstract syntax that actually reflects these concrete
>>> syntaxes and storage schemes?
>>> 
>>> 5. From a pure RDF modeling and semantics point of view, this
>>> proposal should use typed literals and not plain/xsd:string
>>> literals.
>>> 
>>> Best, Richard
>>> 
>>> 
>>> On 22 Aug 2011, at 16:12, Pierre-Antoine Champin wrote:
>>> 
>>>> As I promissed to Richard during the last TC, I'm reactivating the
>>>> thread on his proposal to "lift" the definition of RDF datasets
>>>> into from SPARQL to RDF concepts [1]
>>>> 
>>>> My main concern with this proposal is that it defines a somewhat
>>>> complex structure (the dataset) as a primitive concept in RDF. My
>>>> gut feeling is that we could instead define more basic concepts, on
>>>> top of which SPARQL datasets, SPARQL graph stores, and possibly
>>>> other structures, could be defined. In my understanding, this is
>>>> what the g-* terminology was aiming at.
>>>> 
>>>> In this perspective, back in June, I made an alternate proposal [2]
>>>> for which I got almost no feedback. In a nutshell, it provides a
>>>> minimal vocabulary for reifying RDF graphs into standard RDF, and
>>>> sketches the semantics of such a reification. From there, it
>>>> illustrates how multi-graphs syntaxes (such as Trig) and models
>>>> (such as SPARQL datasets) can be defined on top of it.
>>>> 
>>>> I know that Richard was concerned about several multi-graph models
>>>> had slight differences (e.g. can a BNode be used as a graph name),
>>>> and his solution was to endorse one of them and wait for the others
>>>> to converge. My proposal is rather to provide the building blocks
>>>> for everyone to describe their model in RDF itself, and leave it
>>>> open for different models to coexist, which is ok as long as they
>>>> can all be expressed in plain RDF.
>>>> 
>>>> pa
>>>> 
>>>> 
>>>> [1]
>>>> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/RDF-Datasets-Proposal
>>>> [2]
>>>> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/RDF-Quadless-Proposal
>>> 
>>> 
>> 
>> 
>> -- 
>> Antoine Zimmermann
>> Researcher at:
>> Laboratoire d'InfoRmatique en Image et Systèmes d'information
>> Database Group
>> 7 Avenue Jean Capelle
>> 69621 Villeurbanne Cedex
>> France
>> Tel: +33(0)4 72 43 61 74 - Fax: +33(0)4 72 43 87 13
>> Lecturer at:
>> Institut National des Sciences Appliquées de Lyon
>> 20 Avenue Albert Einstein
>> 69621 Villeurbanne Cedex
>> France
>> antoine.zimmermann@insa-lyon.fr
>> http://zimmer.aprilfoolsreview.com/
>> 
> 
> 
> ----
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> PGP Key: http://www.ivan-herman.net/pgpkey.html
> FOAF: http://www.ivan-herman.net/foaf.rdf
> 
> 
> 
> 
> 
> 
Received on Saturday, 27 August 2011 16:41:49 GMT

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