Re: D-entailment question in http://www.w3.org/TR/2014/PR-rdf11-mt-20140109/

On Jan 30, 2014, at 11:38 AM, Axel Polleres <axel.polleres@wu.ac.at> wrote:

> Hi Richard,
> 
> (not meant to open a new comment, but just to re-explain my original comment)
> 
> On 28 Jan 2014, at 09:35, Richard Cyganiak <richard@cyganiak.de> wrote:
> 
>> Axel,
>> 
>> (Not an official WG response)
>> 
>> The definitions you're looking for are in RDF 1.1 Concepts.
> 
> understood, I am fine with the definitions in that document, but let me re-explain why I was confused:
> 
>>> a) to add more explanatory text or pointers to other specs to make these definitions more self-contained.
> 
> 
> I meant to say it would be nice if there were some more links to the CONCEPTS document or within the MT document to definitions (editorial)

I will work through the document and see if I can make the linking more transparent. 

> , e.g.
>   the word “datatype” in the old RDF-mt spec is directly linked to the definition 
>   http://www.w3.org/TR/rdf-mt/#defDatatype (which was within the document itself, not a part of the Conepts document, which may have confused me)

There is a convention being used here, that internal document links go to the exposition of the relevant idea in that document, and links from there go to other documents, if required. The cost of this to readers is that they may have make two clicks, but the opposite convention would mean that the links would short-circuit the explanatory prose in the document itself. 

A similar editorial style is used for references, where the link in the text goes not to the cited work itself, but to the reference section of the document, where there is an external link to the publication. 

> … if you move the definition to the Concepts doc, that’s ok, but at the moment the choice between explicit references to the concept document at some places, e.g. "RDF literals and datatypes are fully described in Section 5 of [RDF11-CONCEPTS]” and linking directly whenever you use a concept defined herein or in the concepts document (such as “datatype”, defined in CONCEPTS, “L2V” defined herein, but also somewhat in CONCEPTS, though less formally) seems a bit arbitrary at the moment and it would be nice if this was a bit more consistent.

>>> b) explain, even if only in an informal section, how custom datatypes should be defined (which several existing RDF datasets do)

<< As an aside, I fail to see the relevance of the above point about custom datatypes to your next point about "identify". >>

> Particularly, I am not too happy with the definition of the verb “identify” http://www.w3.org/TR/2014/PR-rdf11-mt-20140109/#dfn-identify
> which, frankly is more confusing than enlightning to me… 

This is not so much a definition, as a statement that we are using that word so as to conform to its usage in many other Web publications. 

Let me give an example. Someone might wish to say (in fact, we did not decide to say this, but someone might) that all IRIs in a certain class should be understood to denote the resource that responds with a 200-level coded response when an HTTP GET is executed using that IRI. This is widely, even standardly, described by saying that the IRI "identifies" that resource, so we could phrase this convention as the rule that an IRI in this class shall *denote* whatever it *identifies*, and treat this as a constraint upon interpretations. But in order to be able to even say such a thing, the concepts of "denote" and "identify" must be conceptually distinguished. The semantics document owns the term "denote" for IRIs used in RDF: it *defines* RDF denotation. But it recognizes that other sources and authorities may also define normative mappings from IRIs to what are regarded as their meanings, mappings which it can relate in various ways to the denotation mappings it is defining. The word "identify" is being used as a general catch-all term for any such externally described and conventionally recognized Web naming relationship. 

The application of this usage for datatypes is that we want to say that the relationship of an IRI denoting a datatype, to the datatype it denotes, is established by normal Web conventions external to RDF. We sketch this in the document as follows: 

"In practice, this can be achieved by the IRI linking to an external specification of the datatype which describes both the components of the datatype itself and the fact that the IRI identifies the datatype, thereby fixing a value of the datatype map of this IRI."

If anyone wishes to know how to do this in more detail, I would recommend that they read the XML Schema part 2 documents and use them as a model. 

> "IRI meanings may also be determined by other constraints external to the RDF semantics; when we wish to refer to such an externally defined naming relationship, we will use the word identify and its cognates.”
> 
> in a way, it seems that this wants to tell me that IRIs i may be interpreted as different things

No, that is not what it wants to tell you (and I confess that I do not understand how those words could be interpreted in that way.) What it says is that the meaning of an IRI may be determined by something outside the RDF semantics. That does not imply that the IRI has multiple meanings. (You do agree, I take it, that this can happen, ie that forces external to RDF can, on occasion, determine the intended meanings of IRIs?)

> (as a resource and as a datatype), 
> where the term “identify” seems to be used to implicitly define the (fixed?) interpretaiton function for 
> a datatype, let’s call it I_datatype() but the spec gives only a formal account for I_resource(i), but not 
> for I_datatype(i), whereas it DOES seem to say that 
>   I_resource(i) =  I_resource(j) implies that I_datatype(i) =  I_datatype(j)

> I find the mix of informal and formal definitions here a bit hard to grasp, coming from the IMO fairly clean definition of datatype maps in the old RDF spec. 

The semantic Web *is* a mixture of formal and informal, however, and sometimes we have to face up to that reality :-)

Pat

> 
> HTH to make my comment mor concrete,
> Axel
> 
> 
>> A good understanding of Concepts is sort of a prerequisite for any of the other specs.
>> 
>> Best,
>> Richard
>> 
>> 
>>> On 28 Jan 2014, at 07:53, Axel Polleres <axel.polleres@wu.ac.at> wrote:
>>> 
>>> Dear RDF 1.1 WG,
>>> 
>>> First of all let me thank the WG for their efforts and work on gettin the new RDF1.1 spec to PR.
>>> My new affilation organization (WU Wien) has recently joined W3C and I have started looking 
>>> in a bit more detail into the new specs.
>>> 
>>> When looking over the definition of D-entailment, and also related comments on the list, I have some small question:
>>> 
>>> If I see it correctly, and that’s good news, D-entailment is no longer stacked on top of RDFS Entailment. I very much welcome this change.
>>> Next, I wonder only about one thing regarding the removal of datatype maps. As I understand the discussions, the intention here is 
>>> to simplify things, by assuming that known IRIs *identify* datatypes, i.e. there is a fixed interpretation for such known IRIs, 
>>> and that this fixed interpretation of a datatype IRI aaa is associated with a known lexical-to-value mapping L2V.
>>> 
>>> However, Section 7.1 seems to have no pointers to a *definition* of what is a *datatype* or a *lexical-to-value* actually is, nor give any information of how a custom datatype is defined, e.g. 
>>> 
>>> "For every other IRI aaa in D, I(aaa) is the datatype identified by aaa, and for every literal "sss"^^aaa, IL("sss"^^aaa) = L2V(I(aaa))(sss)”
>>> 
>>> seems to miss that L2V is the associated lexical-to-value mapping for I(aaa).
>>> 
>>> Also, I find the remote definition of *identify* in section 4 ("when we wish to refer to such an externally defined naming relationship, we will use the word identify and its cognates.”)
>>> insufficient to give a proper definition to what a datatype is.
>>> 
>>> I would kindly ask the group for two things:
>>> a) to add more explanatory text or pointers to other specs to make these definitions more self-contained.
>>> b) explain, even if only in an informal section, how custom datatypes should be defined (which several existing RDF datasets do)
>>> 
>>> If I understand this correctly, such informal addition as well as adding explaining text or references to other specs containing the resp. definitions 
>>> would not be a substantial change, and not affect PR status.
>>> 
>>> best regards,
>>> Axel
>>> 
>>> 
>>> 
>>> --
>>> Prof. Dr. Axel Polleres
>>> Institute for Information Business, WU Vienna
>>> url: http://www.polleres.net/  twitter: @AxelPolleres
>>> 
>>> 
> 
> 
> 

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Received on Friday, 31 January 2014 17:52:29 UTC