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Re: [GRAPH] graph deadlock?

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Mon, 19 Dec 2011 11:19:54 +0100
Message-ID: <4EEF0FCA.3020009@emse.fr>
To: public-rdf-wg@w3.org
My impression is that the "Named Graphs" approach is affecting the 
semantics of RDF. It puts constraints on the interpertation of RDF 
graphs. Of course, this has strong consequences on conformant 
implementations of RDF. I would argue that this is not a desirable route 
to follow.

On the other hand, the dataset proposal does not change RDF at all. It's 
just a different data structure, which ultimately rely on RDF but does 
not affect it. Neither does the accompanying semantics add any 
constraint on RDF interpretations.

 From that perspective, I'd say that the Dataset proposal is likely to 
be better accepted.

In fact, maybe RDF Datasets should be described separately from RDF, in 
a different document. To me, RDF datasets serve a different purpose than 
RDF graphs. RDF Dataset is *not* the data model that should be used to 
publish data on the Web. Dataset is the model that is used by *systems* 
managing data or by systems that want to exchange (a lot of) data. 
People should still publish data online in normal RDF.

To make a comparison, if RDF is the HTML of data, a dataset is like a 
whole Web site. You can put a complete Web site in a single ZIP file but 
this is not the way Web documents should be published. HTML does not 
care about multi-webpage sites. Similarly, RDF is the way to publish 
data, and it does not care about multiple graphs.

[1] TF-Graphs/RDF-Datasets-Proposal, Section "Semantics". 

Le 17/12/2011 16:37, Ivan Herman a écrit :
> (I am still on sick leave and will stay for a few more weeks. But I
> am emerging from my torpor, and what better way of doing that is to
> read through a thread on named graphs?:-)
> I have gone through the thread of the past few days, and I have this
> feeling of déjà vu. Although there are some neat things that came up
> (I like Sandro's GSR-s), I have the impression that we are in a
> deadlock.
> Maybe we have to accept the deadlock and move on from there. Namely:
> I have the feeling that we have two notions here, and the group (and
> the community, probably) is just too divided to reconcile those. So,
> maybe, we have to accept that we have two distinct notions here; we
> should document both in the RDF concepts, and try to live our lives.
> The two notions that I see are
> (1) RDF Datasets. It consists of labelled graphs: (G, l), where l is
> an URI. (Some raised the possibility to use literals for 'l', but I
> think there is a consensus to use URI-s). There is no semantic
> relationship between 'G' and 'l', so something like (with an ad-hoc
> syntax here):
> ( {a:b c:d e:f}, mailto:ivan@w3.org }
> is a perfectly o.k. labelled graph in an RDF Dataset
> It seems that most (all?) quad stores fall into this category as well
> as the datasets in SPARQL
> (2) Named Graphs. It is a special RDF dataset, where the label 'l' is
> a (HTTP?) URI with an additional behaviour: if that URI is poked
> (GET-d) then it results in the serialization of a Graph whose parsing
> yields an equivalent graph to 'G'. It is the right/good framework
> for, say, Linked Data, etc.
> Obviously, details are to be filled in.
> My impression is that some in the group (Richard? SteveH?) would like
> to have only (1), whereas others (Sandro, Pat?, TimBL?) would like to
> have only (2). This has been the core of the discussion for 6 months.
> Let us face it, we will _not_ have a consensus here.
> Is it so bad if we acknowledge this, and we clearly document the two
> notions? Both notions can be documented in RDF Concepts, maybe some
> (although I am not sure) in the RDF Semantics. We may think about
> some extra RDF relations among probably named graphs (sub-graph,
> things like that) which probably do not make too much sense for
> labelled graphs. In any case, as long as things are clearly defined,
> implementations, applications, etc, may decide what they do, what
> they expect, etc, and that is fine for interoperability.
> I am not sure how this affects serialization.
> Cheers
> Ivan
> ---- Ivan Herman, W3C Semantic Web Activity Lead Home:
> http://www.w3.org/People/Ivan/ mobile: +31-641044153 FOAF:
> http://www.ivan-herman.net/foaf.rdf

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 Monday, 19 December 2011 10:20:17 UTC

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