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

Re: Really minimal dataset semantics

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Tue, 25 Sep 2012 11:12:21 +0200
Message-ID: <50617575.6060704@emse.fr>
To: public-rdf-wg@w3.org, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
Le 21/09/2012 17:44, Peter F. Patel-Schneider a écrit :
> I don't think that this is converging, even on technical grounds.
>
> My view is that many or most of the use cases in
> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs-UC have to do with talking
> about actual graphs.
>
> My view is that having semantic interpretations of RDF datasets being
> insensitive to the actual named graph doesn't fully support these use
> cases. I'm even a bit worried about defining entailment between RDF
> datasets that doesn't distinguish between equivalent named graphs.

What? At first, you were arguing against any semantics for dataset. Now 
you ask a fairly strong requirement on the semantics, where entailments 
between named graphs are not possible. And recently, you argued in 
favour of a very minimal semantics, where all that is said is, if G 
graph-entail G' then {G} dataset-entails {G'} and <n>{G} dataset-entails 
<n>{G'}.

So what is your position after all?

No semantics fails to solve the use cases where the graph name should 
denote a graph container. Additionally, it fails to satisfy my 
requirement that if G entails G' then <n,G> entails <n,G'>. Each use 
cases where semantics come into play will have to assume there own 
semantics, with no indication from a spec that others would assume the 
same semantics.

A semantics where, in order to make a named graph true, has to associate 
the graph name rigidly with the graph inside prevents all entailments of 
the form "<n>{G} entails <n>{G'}" and even prevents any proper semantic 
extensions to do so.

With the proposed minimal semantics, there is no more support for 
talking about graphs than with no semantics, but at least it solves the 
use cases where one wants to reason separately on named graphs, and it 
does not prevent one to talk about containers or anything else, any more 
than RDF semantics prevents to talk about people, documents, or anything 
else. It also makes it possible to define extensions or vocabularies 
that more formally constrain certain things to be graph containers, for 
instance, in a way that is consistent with the minimal semantics.

If you compare to RDF, that's how things have worked all the time. RDF 
semantics does not satisfy most of the use cases, but it can be used to 
produce vocabularies, semantic extensions, etc that are able to satisfy 
the UCs.



AZ

>
> peter
>
> PS: From http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs-UC I see at least
> 1.1,
>
>
>
> On 09/21/2012 11:33 AM, Antoine Zimmermann wrote:
>> Le 21/09/2012 17:25, Peter F. Patel-Schneider a écrit :
>>>
>>> On 09/20/2012 12:00 PM, Antoine Zimmermann wrote:
>>>> Le 20/09/2012 16:54, Peter F. Patel-Schneider a écrit :
>>>>>
>>
>> [skip]
>>
>>>>>
>>>>> In the semantics there is no notion of a relationship between a
>>>>> name and
>>>>> an actual graph.
>>>>
>>>> In the semantics to which I refer (viz., first version of the Minimal
>>>> dataset semantics) there is a function IGEXT that maps graph IRIs to
>>>> RDF
>>>> graphs. Isn't this a notion of a relationship between a name and an
>>>> actual
>>>> graph?
>>> No, as it does not distinguish between equivalent graphs. Suppose you
>>> have two equivalent graphs, then you can use them interchangeably in
>>> your semantics.
>>
>> If I have 2 equivalent graphs, I can use them interchangeably
>> according to the *RDF semantics*. It's not my fault.
>>
>>
>>>> Or maybe, by "actual graph", you mean a graph that is actually
>>>> "written" in
>>>> a given dataset? Normally, the semantics defines the notion of
>>>> interpretation independently of a given formula, and an interpretation
>>>> makes
>>>> true all sorts of formulas.
>>>>
>>>> In what I propose, for an interpretation to make a named graph true,
>>>> the
>>>> name has to be related (via IGEXT) to whatever graph makes the graph
>>>> inside
>>>> the pair true.
>>>>
>>> Yes, but this doesn't pick out the actual graph, just one of many
>>> possible graphs.
>>
>> If you want the graph inside a <name,graph> pair, just read the
>> dataset. There are APIs for this.
>>
>> Dataset d = loadDatasetFromFile(new File("foo.trig"));
>> Graph g = d.getGraph("http://ex.com/g");
>>
>> That's it.
>>
>>>>
>>>>> If named graphs and RDF datasets are supposed to carry a relationship
>>>>> between a name and an actual graph, then shouldn't the semantics
>>>>> reflect
>>>>> this?
>>>>
>>>> By IGEXT, it does, but a dataset interpretation is not defined in
>>>> function
>>>> of a given dataset, so there is no reason that the name be associated
>>>> with
>>>> the "actual graph" in a given dataset.
>>>
>>> Why not? Isn't a major use case for RDF graphs to record where graphs
>>> (actual graphs, not equivalence classes of graphs) come from?
>>
>> And what's this has to do with semantics?
>> If I want to record someone's speach, I don't need to know the
>> semantics of what he/she says.
>>
>>
>>>>>
>>>>> This is totally different from properties. No one should be arguing
>>>>> that
>>>>> RDF graphs are supposed to carry a relationship between a name and
>>>>> a set
>>>>> of pairs. Instead this is what the semantics does.
>>>>>
>>>>>
>>>>>
>>>>>> (Of course, you
>>>>>>> could always just ignore the semantics and directly use the graph
>>>>>>> from
>>>>>>> the dataset, but then what is the point of having the named graph
>>>>>>> there?)
>>>>>>
>>>>>> The data structure is also very important, just as in RDF graphs, the
>>>>>> data structure is already a nice way of organising the data, linking
>>>>>> data together, etc. Semantics does not have to come into play
>>>>>> where it
>>>>>> has no role.
>>>>>>
>>>>>>
>>>>>> --AZ
>>>>>
>>>>>
>>>>> Huh? If the meaning of a named graph is tied up with relating names to
>>>>> graphs, then the semantics certainly has a role there.
>>>>
>>>> Sorry, maybe I misunderstood what you were saying, but then I don't
>>>> understand your point.
>>>>
>>>> What I'm saying is that, if you find a dataset somewhere in the wild,
>>>> or if
>>>> you have a dataset in memory, you can get the graph associated with a
>>>> graph
>>>> IRI by simply parsing the dataset representation. Semantics does not
>>>> come
>>>> into play in that case.
>>>>
>>>>
>>>> --AZ
>>>
>>> Sure, you can look right in the dataset to find the graph, no semantics
>>> involved. However, if RDF datasets is supposed to be able to carry some
>>> meaning about graphs and their sources then shouldn't its semantics
>>> actually use graphs?
>>
>> No, they are not supposed to carry information about the graph. That's
>> only one use case, and we know there are people against this idea
>> (e.g., the default as merge case). I want the common denominator that
>> would not lead to erroneous entailments according to anybody's
>> understanding of datasets.
>>
>> For metadata about graphs, provenance, dates, whatever, define a
>> vocabulary and make sure that all applications that support the
>> vocabulary interpret it in the same way. It has been done before and
>> it works.
>>
>>
>> AZ
>>
>>>
>>> peter
>>>
>>>
>>
>
>
>

-- 
Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
France
Tél:+33(0)4 77 42 66 03
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/
Received on Tuesday, 25 September 2012 09:16:23 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:25:51 GMT