Re: ISSUE-148: RDF Concepts - IRIs do *not* always denote the same resource

Hi Guus,

I'm sorry, I was holding off on replying to that previous email, pending 
a long conversation with Pat Hayes, in which I hoped to reach a common 
view on this issue.  But apparently I have failed.  :(

No, I cannot live with this.  The current draft of the RDF Concepts says:

   "IRIs have global scope: Two different appearances of an
   IRI denote the same resource.

and that is simply misleading and false, as explained here:

Please let me know what I can do as a next step toward resolving this 
satisfactorily.  Or, alternately, let me know what I should do to 
present this as a formal objection.


On 12/05/2013 06:04 AM, Guus Schreiber wrote:
> David,
> As far as we can see we did not receive a reply from you on this
> response from the RDF WG on ISSUE-148. Could you please indicate whether
> you can live with this?
> Best,
> Guus
> On 06-10-13 20:59, Guus Schreiber wrote:
>> David,
>> The Working Group thanks again you for your concerns on this important
>> aspect of the RDF recommendations, which have been tracked as ISSUE 148.
>> The wording that you mention "IRIs have global scope: Two different
>> appearances of an IRI denote the same resource." is part of the
>> introduction to IRIs in RDF.  Even though this introduction is informal
>> and non-normative and has to be short, it is in fact very important as
>> it sets the tone for the rest of the discussion on IRIs in both Concepts
>> and Semantics. The wording is trying bring forward the idea that every
>> occurrence of an IRI is the *same* identifier, i.e., IRIs are global
>> identifiers.
>> The first part of the wording says this explicitly, but it was felt that
>> some amplification of the point was desirable hence the second part of
>> the wording, emphasizing that different occurrences of IRIs are treated
>> the same in any formal context.  Your concerns have illustrated that
>> this part is not achieving its desired purpose.
>> The working group has two proposals that might address your concerns:
>> 1/ Remove the second part, and make the first part carry the entire load.
>> 2/ Replace the second part with "Two different appearances of an IRI
>> identify the same resource.", which appeals to the non-formal notion of
>> identification instead of the formal notion of denotation.
>> Could you please respond to as to whether
>> either of these changes is satisfactory, and whether you have any
>> preferences between them?
>> Best,
>> Guus Schreiber
>> co-chair RDF WG
>> On 02-10-13 13:23, Guus Schreiber wrote:
>>> Dear David,
>>> Thanks for your comment. We have raised an issue for tracking your
>>> comment [1]. We will get back to you on this.
>>> Best,
>>> Guus, on behalf of the RDF WG
>>> [1]
>>> On 02-10-13 07:05, David Booth wrote:
>>>> In
>>>> I see this statement:
>>>>    "IRIs have global scope: Two different appearances of an IRI
>>>>    denote the same resource."
>>>> This is wrong.  If it were true then there could never be a URI
>>>> Collision
>>>> and there would be no point in the AWWW discussing it or admonishing
>>>> against it.
>>>> An IRI can and often does denote different resources in different
>>>> *interpretations*.  And this, in practice, means that an IRI often
>>>> denotes different resources in different *graphs*, because any graph
>>>> has
>>>> a set of satisfying interpretations, and different graphs may have
>>>> different sets of satisfying interpretations.  For example, suppose
>>>> graphs g1 and g2 have sets of satisfying interpretations s1 and s2,
>>>> respectively, and those sets may be disjoint.  Then colloquially (and
>>>> technically) we can say that an IRI may map to one resource in g1
>>>> (i.e.,
>>>> in some interpretation in s1) and a different resource in g2 (i.e., in
>>>> some interpretation in s2).
>>>> This requires thinking about graphs in terms of sets of satisfying
>>>> interpretations -- an important and valid perspective -- rather than
>>>> assuming that one looks at them only through the lens of a single
>>>> interpretation.
>>>> As a simple example of how a URI can denote different things in
>>>> different graphs, suppose Alice sends this graph G1 from her smart
>>>> phone
>>>> to her home computer to turn *on* her porch light (assuming the usual
>>>> URI prefix definitions):
>>>> G1: {  @prefix db: <>
>>>>         ex:alicePorchLight rdf:value db:x .
>>>>         db:x owl:sameAs ex:on .
>>>>         ex:on owl:differentFrom ex:off . }
>>>> and her light turns on.
>>>> In contrast, Bob sends this graph G2 from his smart phone to his home
>>>> computer to turn *off* his oven:
>>>> G2: {  ex:bobOven rdf:value db:x .
>>>>         db:x owl:sameAs ex:off .
>>>>         ex:on owl:differentFrom ex:off . }
>>>> and his oven turns off.
>>>> It is perfectly reasonable and natural to ask "What resource does db:x
>>>> denote in G1?", and it is reasonable and natural to ask the same of G2.
>>>>   The RDF Semantics (along with OWL) tells us that in G1 db:x denotes
>>>> whatever ex:on denotes, whereas in G2 db:x denotes whatever ex:off
>>>> denotes.   That is useful!  Furthermore, the semantics tells us that if
>>>> we merge those graphs then we have a contradiction -- there are no
>>>> satisfying interpretations for the merge -- and that is useful to know
>>>> also, because it means that Alice and Bob's graphs **cannot be used
>>>> together**.
>>>> Furthermore, the RDF Semantics notion of an interpretation maps well to
>>>> real life applications: in effect, an application chooses a particular
>>>> interpretation when it processes RDF data.  This is a very useful
>>>> aspect
>>>> of the model theoretic style of the semantics.  In this example,
>>>> Alice's
>>>> home control app interpreted db:x to denote "on" and Bob's home control
>>>> app interpreted it to denote "off".  And *both* were correct (in
>>>> isolation): they both did The Right Thing.
>>>> In short, I think the above statement needs to be qualified somehow,
>>>> such as:
>>>>    "IRIs are *intended* to have global scope: Two different
>>>>    appearances of an IRI are *intended* to denote the same resource."
>>>>    (However, the RDF Semantics explains how an IRI may denote
>>>>    different resources in different interpretations.)
>>>> David

Received on Friday, 13 December 2013 19:23:49 UTC