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Re: Making progress on graphs

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 21 May 2012 10:23:31 -0500
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <938206F4-C660-4C82-8456-238383C5CA2A@ihmc.us>
To: Guus Schreiber <guus.schreiber@vu.nl>

On May 18, 2012, at 1:17 PM, Guus Schreiber wrote:

> All,
> I'd like to return this thread to where it was started for. We seem to be going into corner cases quite a lot (ISSUE 22 - empty graphs -, for example). I think we should focus more on what we agree on. I listed the issues mentioned by Richard for the telecon of this week, but we didn't get to them, so they will be in next week's agenda. Here they are (slightly edited/extended version of Richard's original ones):
>    ISSUE-5 Graph literals http://www.w3.org/2011/rdf-wg/track/issues/5
>    PROPOSED: Close ISSUE-5 ("Should we define Graph Literal datatypes?"),
>    saying No, we should not.
>    ISSUE-28 Syntactic nesting of g-texts http://www.w3.org/2011/rdf-wg/track/issues/28
>    PROPOSED: Close ISSUE-28 ("Do we need syntactic nesting of graphs (g-texts) as in
>    N3?"), saying No, we do not -- they are useful, but we can provide the same
>    functionality with datasets.

Can you (or anyone) explain how this functionality is provided with datasets? A simple example will suffice. 

>    ISSUE-29 Do we support SPARQL's notion of "default graph"?
>    http://www.w3.org/2011/rdf-wg/track/issues/29
>    PROPOSED: Close ISSUE-29 (Do we support SPARQL's notion of "default graph"?'),
>    Yes, we do.

I would like us to clarify what we mean by "support" here. If it just means that datasets have an optional default graph in them, then I am fine with that decision. If it means more, I'd like to know what more. 

>    ISSUE-30 Relation RDF Datasets with multiple graphs
>    http://www.w3.org/2011/rdf-wg/track/issues/30
>    PROPOSED: Close ISSUE-30 ("How does SPARQL's notion of RDF dataset relate our
>    notion of multiple graphs?"), saying we will use SPARQL's notion of RDF dataset as
>    much of the foundation of our handling of multiple graphs.
>    ISSUE-33 Mechanism to refer to sub-graphs and/or individual triples
>    http://www.w3.org/2011/rdf-wg/track/issues/33
>    PROPOSED: Close ISSUE-33 ("Do we provide a way to refer to sub-graphs and/or
>    individual triples?"), with the understanding that datasets can be used to refer to
>    sub-graphs and individual triples.

Again, how does this work? Consider the graph G = { <:a :b :c> <:d :e :f> <:g :h :i>} and the subgraph G1 consisting of just the first two triples, and then the first triple alone, call that T. That is a total of three triples and two (or perhaps three) graphs. How would these relationships be represented using datasets? 


> Also, I would like to focus your attention to Sandro's document [1]. I tried to get discussion on the fact there is lot of stuff there we appear to agree on [2], but I miserably failed because my inadvertent subject line dominated the debate. Please comment on Sandro's document if you have time.
> Best,
> Guus
> [1] http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-spaces/index.html#
> [2] http://lists.w3.org/Archives/Public/public-rdf-wg/2012May/0372.html
> On 13-05-2012 16:59, Richard Cyganiak wrote:
>> All,
>> We've been talking our way up and down the design space for multigraphs for a year now, with not much to show for it. We still have not settled on a basic design.
>> Once we do settle on a basic design, the real work only starts since we need to nail down the details. This will take time. Our charter says that all documents should go to LC *this month*, and obviously we are nowhere near ready for this.
>> So I think it's time to stop exploring the design space, and start collapsing it by making decisions.
>> Obviously there is still strong disagreement on many things when it comes to multigraphs, but it seems to me that all proposals on the table accept a basic *abstract syntax* that is quite similar to the RDF datasets in SPARQL, and even the most adventurous experiments don't really stray from that forumla. Therefore:
>> PROPOSAL: The abstract syntax for working with multiple graphs in RDF consists of a default graph and zero or more pairs of IRI and graph. This resolves ISSUE-5 (“no”), ISSUE-22 (“yes”), ISSUE-28 (“no”), ISSUE-29 (“yes”), ISSUE-30 (“they are isomorphic”), ISSUE-33 (“no”).
>> RATIONALE: All proposals on the table are based on an abstract syntax very similar to SPARQL's notion of an RDF dataset, although there is no consensus on the semantics and the terminology. Making a decision on the basic abstract syntax would unblock the work, and allow various strands of required detail work to proceed independently, hopefully leading to additional resolutions to remaining questions, such as:
>>   • What's the formal semantics of the abstract syntax?
>>   • Definition of the concrete syntaxes (N-Quads, etc.)
>>   • Describing how to work with this in the Primer
>>   • What do call the pairs? “Named graphs” or something else?
>>   • What to call the entire thing? “RDF dataset” or something else?
>>   • Can blank nodes be shared among graphs?
>>   • What additional terminology (rdf:Graph etc) needs to be defined?
>> Best,
>> Richard

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Received on Monday, 21 May 2012 15:24:29 UTC

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