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Re: RDF Semantics Editors Draft?

From: Ivan Herman <ivan@w3.org>
Date: Fri, 4 May 2012 17:32:36 +0200
Cc: Richard Cyganiak <richard@cyganiak.de>, David Wood <david@3roundstones.com>, Pat Hayes <phayes@ihmc.us>, public-rdf-wg WG <public-rdf-wg@w3.org>
Message-Id: <6079BE1F-E8C7-4970-A0F1-105925AA8C80@w3.org>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
Peter,

Let us start with where this issue comes from: experience shows that the model theoretical part of the document is unpalatable for most of our developers, while rules are not. Put it another way, if somebody wants to understand what RDF(S) inferencing means and produces then (with some exceptions) the right way is to show them the rules: those are clear and understandable for anybody having a programming experience (well, most of them are at least; the association of a literal with a fresh bnode is fairly obscure, too, I must admit). 

Model theory remains an obstacle for most of them. Worse: for many people that was/is one of the reasons they reject RDF altogether (or, at least, they reject anything related to inferencing).

Putting all the rules into RDF Concepts is compelling, of course. But in doing so, I am afraid the number of people ever looking at the RDF Semantics document will be reduced even more because everything they need will be in Concepts. And that might be valid for implementers, too. This may be a good thing, but I am not sure.  At the moment, I am still more in favour of reorganizing the Semantics document by pulling rules to the fore, and pushing the model theory as a second part that is clearly labelled as a very theoretical aspect of RDF.

I am not sure what is missing from the rules, b.t.w.; I argue that they should be complete.

Ivan


On May 4, 2012, at 16:10 , Peter F. Patel-Schneider wrote:

> Even with these arguments, I think that changing things around is a horrible idea.  My view is that the model theory needs to remain normative and the rules informative.
> 
> Consider what would have happened if the reverse was true in 2004.  The rules in the document are incomplete, but making them normative would have meant that RDF was defined in a way that made certain semantically valid inferences incorrect!
> 
> Even if the rules have been proven to be complete, there is no reason that implementers of RDF or authors of RDFS ontologies should even know that the rules exist.   What needs to be implemented or considered is not the rules, but the meanings.  RDF implementations can be done in any way that respects the semantics.  RDFS ontologies can be considered in any way that respects the semantics.   No rules needed at all!
> 
> I even think that including the rules at all in the RDF Semantics document was a mistake.  If the WG is considering making a change in the status or position of the rules, I argue that they should be taken out of RDF Semantics and put into RDF concepts!
> 
> I think that it might be a good idea to put a warning at the beginning of the document telling people that this is a formal description of the semantics of RDF and that readers should be first familiar with several of the other RDF documents.
> 
> peter
> 
> 
> On 05/04/2012 07:53 AM, Richard Cyganiak wrote:
>> Hi Peter,
>> 
>> On 4 May 2012, at 09:52, Peter F. Patel-Schneider wrote:
>>> Well I think that it would be a horrible idea to deemphasize the semantics.
>>> 
>>> I'm also completely unsure as to what name could be any better than RDF Semantics.
>> Let's consider who reads the RDF Semantics document, and for what reasons. From what I gather, we can identify a number of different cases. I'm sure there are many more:
>> 
>> 1) Spec writers read it, in order to understand how to make their specifications compatible with other specifications in the RDF stack. For example, neither the RDB2RDF WG nor the SPARQL WG could have done its work without knowing the things formally specified in RDF Semantics.
>> 
>> 2) Implementers of various specs (incl. RDF, RDF Schema, SPARQL) read it, in order to understand how their systems should behave, especially with regard to datatypes and RDFS inference.
>> 
>> 3) Authors of RDF Schema vocabularies read it, in order to understand the consequences of declaring domains, ranges, subproperties and so on.
>> 
>> 4) RDF newbies read it, because this is where they happened to end up after some googling or link-clicking and they don't understand the big scheme of things yet.
>> 
>> How well does the current document serve these needs?
>> 
>> For 1), I think it works well.
>> 
>> For 2) and 3), I think the document as it stands does not serve these readers well, and it could do a *much* better job. We have reports that such readers tend to find the informative entailment rules in Section 7 extremely useful, and much of the rest of the document rather impenetrable. It has thus been suggested that the entailment rules should be given more prominence. One minimally invasive way of achieving this would be to just move the words “normative” and “informative” around a bit. I suppose this is what Ivan refers to when he says “reorganize to make the rules normative and deemphasize the model-theoretic semantics”.
>> 
>> For 4), the document as it stands doesn't work at all, and it can't, because that's not its purpose. In fact, when newbies try reading this document, it's pretty much guaranteed to end in disaster. I think we all agree that this is *not* the document you should be looking at in your first encounter with RDF. There isn't *too* much we can do about this, but I think that a title that is a bit scarier to newbies could help. Can we put something like “model theory” or “formal representation logic” into the title?
>> 
>>> Of course, if the WG wants to make RDF no longer be a formal representational logic, then ....
>> I thought RDF is a data model?
>> 
>> Best,
>> Richard
>> 
>> 
>> 
>>> peter
>>> 
>>> 
>>> On 04/25/2012 11:27 AM, David Wood wrote:
>>>> Hi Peter and Pat,
>>>> 
>>>> The RDF WG briefly discussed the need for an RDF Semantics editors draft at today's telecon.  I am aware that there are a lot of open issues and therefore hard to produce a draft, but perhaps it makes sense to have a single document that lists the issues in one place.
>>>> 
>>>> In any event, we would like to discuss this at next week's telecon if you can make it.  Thanks.
>>>> 
>>>> Relevant comments from IRC (no log published yet since the meeting isn't over):
>>>> [[
>>>> ivan: one thing that came up early was discussion to change title of RDF Semantics document, reorganize to make the rules normative and deemphasize the model-theoretic semantics AlexHall @ 11:20
>>>> ... think it's a good thing to do but huge amount of editorial work AlexHall @ 11:20
>>>> cygri: is there an editors draft of RDF Semantics yet? 11:21
>>>> [no] 11:21
>>>> cygri: given that there are larger changes to the doc, would feel better if there were an editors draft by now. 11:21
>>>> guus: suggest we should put it on the agenda for next week
>>>> ]]
>>>> 
>>>> Regards,
>>>> Dave
>>>> 
>>>> 
>>>> 
>>>> 
> 


----
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
Received on Friday, 4 May 2012 15:30:02 GMT

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