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Re: More clearly warn that "generalized RDF" is non-standard

From: Sandro Hawke <sandro@w3.org>
Date: Sun, 04 Aug 2013 07:57:34 -0400
To: Pat Hayes <phayes@ihmc.us>,David Wood <david@3roundstones.com>
CC: David Booth <david@dbooth.org>,public-rdf-comments <public-rdf-comments@w3.org>
Message-ID: <6091ea6c-ffe3-4078-8a58-392c23377a2f@email.android.com>


Pat Hayes <phayes@ihmc.us> wrote:
>The terminology is already out there, eg
>http://www.w3.org/TR/owl2-profiles/ is a Rec from 2012 which defines
>and uses the idea (see
>http://www.w3.org/TR/owl2-profiles/#Reasoning_in_OWL_2_RL_and_RDF_Graphs_using_Rules),
>and  http://www.w3.org/TR/rif-rdf-owl/ is a 2013 Rec which has been a
>Candidate Rec since 2009

Actually a REC since 2009.   Otherwise I agree with all this.     :-)     Hopefully we can add a little text to RDF Concepts so others understand this before starting a thread on the comments list.   Assuming that text is okay, would you be satisfied, David Booth?

     - Sandro

also defines and uses it.  (see
>http://www.w3.org/TR/rif-rdf-owl/#Syntax_of_RIF-RDF_Combinations ). The
>second one also has this in its "end note" (my emphasis added): 
>
>"Generalized RDF graphs: Standard RDF graphs, as defined in
>[RDF-Concepts], do not allow the use of literals in subject and
>predicate positions and blank nodes in predicate positions. The RDF
>Core working group has listed two issues questioning the restrictions
>that literals may not occur in subject and blank nodes may not occur in
>predicate positions in triples. ***Anticipating lifting of these
>restrictions in a possible future version of RDF***, we use the more
>liberal notion of generalized RDF graph. We note that the definitions
>of interpretations, models, and entailment in the RDF Semantics
>document [RDF-Semantics] also apply to such generalized RDF graphs."
>
>Apparently their anticipation was misguided, but I can attest that
>almost any expressive extension of RDF would be easier and more
>naturally defined on generalized RDF than standard RDF, regardless of
>its lack of normativity. So it *will* get used. I don't think we should
>discourage or encourage, just state the facts about what is normative.
>Discouraging the use of generalized RDF amounts to discouraging the use
>of RIF and OWL2 and JSON-LD and discouraging the use of complete RDF
>reasoners, among other foolish things to try to discourage. We are in
>the minority on this issue. 
>
>I think DavidB's concerns might be alleviated if we could call it by a
>different name, because "generalized RDF" does sound like a kind of
>RDF. But this name is already in use, so to change it now might cause
>more confusion. As usual, writing standards is a lose/lose situation. 
>
>Pat
>
>
>On Aug 2, 2013, at 8:22 AM, David Wood wrote:
>
>> Yes, I concur with Sandro.  The RDF WG inserted the "generalized RDF"
>description for a good reason.  It is there to allow for alignment with
>JSON-LD and any future implementations or formats that cannot, for good
>technical reasons, limit their possible parsings to standard RDF.
>> 
>> That does not mean, however, that we should encourage "generalized
>RDF" at any point.  Its use should be strongly discouraged in
>implementations and where that is impossible, as with JSON-LD, then its
>/social/ use should be strongly discouraged, as with JSON-LD.  Hence, I
>think we should put in the stronger wording but leave the concept in
>place.
>> 
>> Chair and editor hats simultaneously "on" and "off".  Take that,
>Erwin Schrödinger!
>> 
>> Regards,
>> Dave
>> --
>> http://about.me/david_wood
>> 
>> 
>> 
>> On Aug 2, 2013, at 09:15, Sandro Hawke <sandro@w3.org> wrote:
>> 
>>> Speaking just for myself, I think this is going too far.   I think
>it does a service to the community to define the term "generalized RDF"
>in RDF concepts, since (1) it's used in at least two of our specs which
>we'd rather not have depend on each other (JSON-LD and RDF Semantics),
>and (2) it's something people come up with on their own anyway, and
>this way we tag the discussions about it.  It's hard to evolve or
>extend a standard  interchange format, but the best hope for doing so
>is to have everyone who wants to add some feature add it in the same
>way and talk about it the same way.   By defining "generalized RDF" in
>RDF Concepts, I think we're doing that.
>>> 
>>> All that said, I think it would be a good idea to add something like
>the warning note you propose, and perhaps some of the explanation I
>just provided.   That is, roughly: Generalized RDF is not standard RDF,
>but it can be useful and is reasonable to use among systems which have
>all agreed to use it.  If you try to send it to systems which have not
>agreed to use it, it won't work.
>>> 
>>>      -- Sandro
>>> 
>>> On 08/01/2013 04:17 PM, David Booth wrote:
>>>> I've been thinking further about this, and I have another more
>radical suggestion.
>>>> 
>>>> It seems to me that including even an informative definition of
>"generalized RDF" in the RDF spec substantially increases the risk that
>someone may mistakenly believe that "generalized RDF" is some form of
>standard RDF, when it is not. It is an extension of RDF that does not
>conform to the RDF standard. Hence it is all the more important to
>visibly warn readers about the use of generalized RDF.
>>>> 
>>>> Actually, the more I think about it the more I am convinced that
>the inclusion of the definition of "generalized RDF" in the RDF spec
>**at all** is a big mistake, because it substantially increases the
>risk that someone may mistakenly believe that "generalized RDF" is some
>form of standard RDF, when it is not.
>>>> 
>>>> Thus, my second suggestion is to entirely remove the definitions of
>generalized RDF triple, graph and dataset from the RDF Concepts
>document
>>>>
>https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#section-generalized-rdf
>
>>>> 
>>>> If the RDF Semantics document needs to define the notion of
>generalized RDF to simplify the semantic rules, then I guess a
>definition could be included in that document, *with* a big fat warning
>saying that this definition is included only to simplify the
>specification of the formal semantics, and does not constitute a part
>of the RDF standard.
>>>> 
>>>> David
>>>> 
>>>> 
>>>> On 08/01/2013 11:20 AM, David Wood wrote:
>>>>> Hi David,
>>>>> 
>>>>> I acknowledge your comment and your concern.  I *personally* agree
>with
>>>>> you that we need to carefully word this section of RDF Concepts.
>>>>> 
>>>>> The next RDF WG meeting that I will be able to attend is 21
>August,
>>>>> so I will put this on the agenda for that meeting.
>>>>> 
>>>>> Regards,
>>>>> Dave
>>>>> -- 
>>>>> http://about.me/david_wood
>>>>> 
>>>>> 
>>>>> 
>>>>> On Aug 1, 2013, at 10:28, David Booth <david@dbooth.org> wrote:
>>>>> 
>>>>>> Section 7 defines the notion of "generalized RDF", triples and
>datasets, but does not adequately warn that "generalized RDF" is
>non-standard. Case in point: this has already led to some discussion in
>the JSON-LD group about whether "generalized RDF" is a form of standard
>RDF.
>>>>>> 
>>>>>> I suggest rewording section 7 to the following, using a "NOTE"
>call-out:
>>>>>> [[
>>>>>>   <p>It is sometimes convenient to loosen the requirements
>>>>>>   on <a>RDF triple</a>s.  For example, the completeness
>>>>>>   of the RDFS entailment rules is easier to show with a
>>>>>>   generalization of RDF triples.   </p>
>>>>>> 
>>>>>>   <p>A <dfn>generalized RDF triple</dfn> is an RDF triple
>>>>>>   generalized so that subjects, predicates, and objects
>>>>>>   are all allowed to be IRIs, blank nodes, or literals.
>>>>>>   A <dfn>generalized RDF graph</dfn> is an RDF graph of
>>>>>>   generalized RDF triples, i.e., a set of generalized RDF
>>>>>>   triples.  A <dfn>generalized RDF dataset</dfn> is an RDF
>>>>>>   dataset of generalized RDF graphs where graph labels can
>>>>>>   be IRIs, blank nodes, or literals.</p>
>>>>>> 
>>>>>>   <p class="note" id="note-generalized-rdf"> Any users of
>>>>>>   generalized RDF triples, graphs or datasets need to be
>>>>>>   aware that these notions are non-standard extensions of
>>>>>>   RDF and their use may cause interoperability problems.
>>>>>>   There is no requirement on the part of any RDF tool to
>>>>>>   accept, process, or produce anything beyond standard RDF
>>>>>>   triples, graphs, and datasets. </p>
>>>>>> ]]
>>>>>> 
>>>>>> Thanks,
>>>>>> David
>>>>>> 
>>>>> 
>>>> 
>>>> 
>>> 
>>> 
>> 
>
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Received on Sunday, 4 August 2013 11:57:28 UTC

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