W3C home > Mailing lists > Public > public-rdf-comments@w3.org > August 2013

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

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 2 Aug 2013 11:10:14 -0700
Cc: Sandro Hawke <sandro@w3.org>, David Booth <david@dbooth.org>, public-rdf-comments <public-rdf-comments@w3.org>
Message-Id: <7D7158AD-BC75-4832-88A1-F194CC1DAF9E@ihmc.us>
To: David Wood <david@3roundstones.com>
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, 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 Friday, 2 August 2013 18:10:44 UTC

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