Re: RDF Extensibility

On 07/06/2010 11:05 PM, Pat Hayes wrote:
> 
> On Jul 6, 2010, at 9:34 AM, Jiří Procházka wrote:
>>
>> [snipped]
>>
>> In case of a) I don't have cleared up my thoughts yet, but generally I
>> would like to know:
>> How are semantic extensions to work together in automated system?
> 
> Well, the semantics always defines some notion of entailment, and your
> system is supposed to respect that notion: not draw invalid conclusions,
> draw as many valid conclusions as you feel are useful, don't say things
> are inconsistent when they aren't, etc.. Otherwise, you have free rein.
> So, if you have several semantic extensions, they are each provide a set
> of such entailments and they should add up to one single set of legal
> entailments.
> 
>> How to let agent know that the data is described using new RDF
>> extension, which the client doesn't know and the data could be (or
>> definitely are) false if it is interpreted using vanilla RDF semantics?
> 
> NOt false, if its a semantic extension (they can't contradict the RDF
> semantics., only extend it.) BUt same point more generally: how do we
> know, given some RDF, what semantic extensions are appropriately to be
> used when interpreting it? That is a VERY good question. This is
> something that RDF2 could most usefully tackle, if only in a first-step
> (ham-fisted?) kind of a way. We were aware that this was an issue in the
> first WG, but it was just too far outside out charter, and our energy
> level, to tackle properly. One obvious (?) thing to say is that using a
> construction from a namespace which is associated with the definition of
> any RDF semantic extension is deemed to bring along the necessary
> interpretation conditions from the extension, so that for example if I
> use owl:sameAs in some RDF, then I mean it to be understood using the
> OWL semantic conditions. We all do this without remarking upon it, but
> loosely, and to make this precise and normative would be a very
> interesting (and useful) exercise. (An issue already here is, which
> version of the OWL semantics is intended? Does the use in RDF also
> "import" the OWL-DL syntactic restrictions on its use, for example?)

That is indeed what I had in mind. I think sooner or later this has to
be dealt with, and I think the sooner the better...

I don't think the namespace thing is obvious, since I don't think there
is a concept of namespace defined in RDF. It is just some graph
containing some terms related to a semantic extension of RDF. How does
the processing application know? Which entailment rules are to be
applied to the graph? How should the patterns triggering application of
a rule be defined? Having multiple rulesets, in what order and how to
apply them? What about rules modifying rules and rulesets? How to define
interpretation of graphs (which rulesets to apply, which to ignore)? Is
a graph and entailment rules everything what is used in interpretation
according to a semantic extension or are there also some attributes like
graph consistency (if so, how do pass them on? as added triples?)?
These are just questions I am pulling off top of my head...

Best,
Jiri

> Pat
> 
> 
>>
>> b) How should my system know that the data which is just being processed
>> is new revision of RDF/XML and not malformed RDF/XML when forward
>> compatibility was out of sight, out of mind when RDF/XML was designed?
>>
>> Best,
>> Jiri Prochazka
>>
> 
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