W3C home > Mailing lists > Public > public-rdf-wg@w3.org > May 2012

Re: Making progress on graphs

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 14 May 2012 01:34:16 -0500
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, Sandro Hawke <sandro@w3.org>
Message-Id: <7C6D21C1-4FA0-4211-B6AF-E60FF3B3BA3D@ihmc.us>
To: RDF Working Group WG <public-rdf-wg@w3.org>
Accepting Richard's proposal for syntax, we can try moving on to some decisions for semantics. Here, I think Sandro has a point: there are some large-scale top-down decisions to be made, and until we get these clear, arguing about details will only produce muddle. 

I can discern three main ideas that the WG has produced for a semantics for datasets. All of these treat the default graph as being, well, just a graph, so I will ignore this. They differ in how they interpret the name-graph pairings.

1. (Peter) Datasets have no special semantics. People are free to use them however they find most useful. There is no notion of asserting a dataset (or maybe: asserting a dataset is just asserting its default graph.) 
2. (Sandro) Datasets are used to attach names to graphs, so that the name can be used to refer to the graph in other content, in particular, in other RDF. Asserting the dataset is a form of graph baptism.
3. (Antoine) Datasets are used to assert graphs in contexts, so that the name indicates a context of interpretation for the IRIs in the named graph. Asserting the dataset is a making a statement in a kind of context logic version of RDF.

If anyone knows of any others, let them speak now or forever hold their peace. 

I suggest that until we can decide which of these overall pictures is best, any discussion of details of semantics is irrelevant. 

The arguments I have heard for and against are as follows. 

1. Pro: makes life simple, and allows the world to continue to experiment freely. Con: Allows the world to experiment freely, so blocking interoperability. Does not provide a way to name graphs.
2. Pro: provides a way to name graphs, which is needed. Con: is not the way that datasets are used in current practice.
3. Pro: corresponds to current actual usage. Con: based on a 'localist' view of IRI meanings which violates current assumptions or maybe best practice (?). Does not provide a way to name graphs. Requires change to RDF semantics.

FWIW, I observe that the proposal outlined in http://www.w3.org/2011/rdf-wg/wiki/AnotherSpin  allows one to express Antoine's content while using Sandro's naming semantics, which might be a way to reconcile things. 

Pat

On May 13, 2012, at 4:29 PM, Sandro Hawke wrote:

> On Sun, 2012-05-13 at 23:09 +0200, Antoine Zimmermann wrote:
>> +1 to the proposal and to move forward one piece at a time.
> 
> I think our decisions should be choices between complete solutions or
> pieces of complete solutions.
> 
> Otherwise we risk having no solutions, or only bad solutions, because we
> constrained the solution space blindly.
> 
> Richard's proposal (with some minor tweaks in how he defined dataset
> [1]) happens to be in line with my proposal, but I'm rather opposed to
> it as a matter of principal; I don't see how chopping up the design
> space like this is going to produce better results, and I'm quite
> concerned it will make things worse.
> 
> Please, just paint complete pictures, showing how to address all the use
> cases, or at least some interesting ones.  Then we can look at those
> pictures and decide among them.
> 
> (Antoine, you kind of did this.  We've never talked about your
> proposal.  I happen to strongly prefer mine, but yours did make sense.)
> 
> What we can do -- and maybe this is would be enough for what you want,
> Richard -- is make non-binding strawpolls to try to understand where
> people are coming from and what design features they are likely to
> support.
> 
>   -- Sandro
> 
> [1] Specifically: can the IRIs occur more than once?  I assume we'd
> agree not.  More controversially, can named graphs be empty?  I'd argue
> no, in order to keep compatibility with quad stores.   SPARQL 1.1 Update
> struggles with this, saying EG you can create an empty graph but it
> might be instantly deleted.
> 
> 
>> 
>> Le 13/05/2012 22:54, Richard Cyganiak a écrit :
>>> Hi Ivan,
>>> 
>>> On 13 May 2012, at 16:15, Ivan Herman wrote:
>>>> it looks to me that Sandro's draft document:
>>>> 
>>>> https://dvcs.w3.org/hg/rdf/raw-file/d96c16480e42/rdf-spaces/index.html
>>>> 
>>>> 
>>>> 
>> would be a good way to 'settle' things (see [1]), too.
>>> 
>>> Sandro's draft takes explicit position on a *all* issues, many of
>>> which are highly controversial. By bundling non-controversial and
>>> controversial issues all into one big package, this blocks progress
>>> on the sub-issues where we actually seem to all agree. So I repeat:
>>> 
>>> 
>>> 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”).
>>> 
>>> 
>>> So far I have heard no objections to this.
>>> 
>>> Best, Richard
>>> 
>>> 
>>> 
>>>> At the moment it seems to collect all the various issues that we
>>>> have discussed with a fairly clear way of moving forward.
>>>> 
>>>> Ivan
>>>> 
>>>> 
>>>> [1]
>>>> http://lists.w3.org/Archives/Public/public-rdf-wg/2012May/0178.html
>>>> 
>>>> 
>>>> 
>>>> 
>> On May 13, 2012, at 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
>>>> 
>>>> 
>>>> ---- 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
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>>> 
>>> 
>> 
> 
> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Monday, 14 May 2012 06:34:57 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:25:48 GMT