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Re: Denotation of datatype values

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Mon, 15 Apr 2002 16:33:11 -0400
Message-Id: <p05101517b8e0e6008df2@[65.217.30.94]>
To: Patrick Stickler <patrick.stickler@nokia.com>
Cc: w3c-rdfcore-wg@w3.org
>On 2002-04-10 22:13, "ext Jeremy Carroll" <jjc@hplb.hpl.hp.com> wrote:
>
>>
>>  Patrick:
>>>  But it seems that no'one (myself included) feels that the
>>>  answer is 'yes' (apart from perhaps Jeremy, though he has
>>>  not responded to this question directly) so I'll drop it.
>>
>>  Whilst it is good of you to keep thinking of me, I have decided that I am
>>  too far from the group consensus to contribute positively to the process.
>>
>>  I have lost quite what the "question" refered to above was, but it seems
>>  that the e-mail has settled on a rational point (which I disagree with).
>>
>>  In some contexts the literal string "25" in the model theory denotes the
>>  literal string "25" but "according to our shared understanding" there is a
>>  corresponding value of 25. The 25 does not occur in the model theory, but
>>  the application is expected to use it.
>>
>>  Personally I detect doublethink. If the specification indicates that the
>>  application should use 25 when it receives "25" then wherever the official
>>  line at which the model theory stops there is an implicit and
>>  ill-articulated extended conceptual model which has the value 25 in it. That
>>  is the conceptual model that the specifications expect the application
>>  writer to use (and document authors ...).
>
>Well it may be ill-articulated (I'm working on that ;-) but it's meant to
>be explicit (and this thread is very useful in nailing down where the WD
>fails to communicate).
>
>The section on "Datatyped Literals" attempts to both explicitly define
>this conceptual model and also states that it is the focus of RDF
>Datatyping.
>
>The goal of RDF Datatyping is to provide applications with Datatyped Literal
>pairings.

I think that this way of phrasing it might be potentially misleading, 
since it suggests that the pairings are actually in the MT.

>The application you reference does not recieve "25". Rather, it recieves
>the datatyped literal pairing <xsd:integer, "25">,
>and there are three different idioms by which that datatyped literal can
>be represented. If the application only gets "25", then it can't derive
>any datatype value from that *insofar as* the RDF knowledge is concerned.
>(it might guess that it is some kind of number, but it won't be able
>to know for sure; it could be a monthday, or in octal notation, etc.).
>
>I do admit that this conceptual model of datatyped literal pairings is
>at a level above the graph MT proper, and the MT and datatyping MT apply
>only to the idioms than to what the idioms fully represent. A datatyped
>literal pairing has no explicit definition in the MT nor any explicit
>denotation in the graph.

Which is why it might be best omitted, maybe? At least from a first 
explanation.

>The implicit representation in the idioms
>is the closest you get to it at that level.
>
>Another difference between the datatyped literal conceptual level and
>the MT graph level is whether the value itself has explicit
>denotation in the graph, and in the case of the inline idiom it doesn't
>yet at the datatyping interpretation level it does (given complete
>idioms) which is why it seems that there is "doublethink" going on.
>But just because the value doesn't have denotation in the graph doesn't
>mean that any "doublethink" is going on. These are, after all, different
>levels -- and the higher level is not changing the interpretation
>of the lower level, it simply clarifies it, making explicit what
>is implicit at the lower level.
>
>Alot has to do with perspective and expectation. If you are
>expecting the property to always have a datatype value, and you
>are looking at the MT level, you will then be disappointed to
>find a literal. If, however, you are looking at the datatyping
>level, then you will find an unambiguous representation of
>a value (the datatyped literal pairing), which may still
>disappoint you, if you want the actual explicit value. At the
>highest level, then, with full understanding of the datatype
>you will finally get the actual value you are looking for.
>
>The MT defines the graph syntax and certain constraints on the
>datatyping idioms. Those idioms serve to communicate datatyped
>literal pairings (though the implicit/global idioms without
>rdfd:range constraints will be incomplete) and the datatyping
>MT helps to achieve consistency in the interpretation of those
>idioms in deriving datatyped literal pairings from them.
>
>An application which is concerned with datatyped values will look
>for the idioms that will provide it with the datatyped literal
>pairings, and if it groks the datatype in question, will be
>understand which is the value identified by the datatyped literal
>pairing.
>
>Applications which are only concerned with the literal graph
>syntax will have a solid MT by which to interpret the idioms,
>along with the rest of the graph, in terms of the MT.
>
>I don't see a problem to having these different levels. In fact, an RDF
>API could provide separate access at all three levels shown in my
>"Levels of Interpretation" section. At the first level, property
>values such as ex:age are simply graph nodes; either literal nodes
>or non-literal nodes. At the second level, property values are
>extra-RDF conceptual objects denoting datatyped literal pairings
>(the idioms in the literal graph are hidden). At the third level,
>property values are the actual values, in the native, system-specific
>representation (presuming the API groks the datatypes in question
>and the system is able to provide a native representation).
>
>The separation of the MT/Idiom level from the conceptual datatyped
>literal pairing level also gives us more liberty in the future
>for defining new idioms (e.g. if literals become subjects) with
>little to no impact to the higher levels based on the abstraction
>of datatyped literal pairings.

I don't want to be a party-pooper, but I honestly feel that having an 
MT and sticking to it is one way to get past this kind of 
half-formalized (and rather confusing) kind of discussion. I do not 
know what these 'levels' are supposed to be, or how to recognize 
them, or how to evaluate talk about them, etc. etc. . Why not stick 
to the syntax and the MT, and just talk about that? Then everything 
is clear. What an application wants to do with an RDF graph is up to 
it, not up to us. All we can do is to provide application writers 
with a gold standard for meanings, and leave other 'layers' to them.

>
>While we may want to re-examine extending the Datatyping MT to
>provide some explicit definition of datatyped literal pairings,
>the separation of levels between idioms and those pairings is,
>I think, a good thing.

Maybe, but I don't think its our business to go past explaining the 
meanings of our idioms, and leave anything else to someone else. That 
would include pairings.

>
>>  My earlier argument that the
>>  datatyping proposal was non-monotonic is refuted up to the model theory.
>>  This is from the clarity that there is only "25" and not 25. But the
>>  argument still stands as far as the conceptual model goes.
>
>I appreciate this point, really.
>
>But I don't see any real non-monotonicity
>here, given we are talking about two distinct levels of interpretation,
>not the same level of intepretation.
>
>Neither level is non-monotonic, and the datatyping level only clarifies
>but does not change the knowledge at the lower idiom level, so the
>transition between levels also is not non-monotonic.
>
>The complaint may then really be about having the different levels
>of interpretation, rather than addressing everything at the MT level.

Oh dear. What other levels of interpretation are there? Do we have to 
define them? (HOW??)

>
>My question which started this thread was really trying to determine
>if these different levels were going to cause any problems to anyone
>(e.g. DAML, OWL, etc.) and if so, whether we should do anything about
>it. The present concensus (by measure of silence ;-) is that it is
>not a problem.
>
>>  It seems that the clarity of this thread that one idiom delivers 25 whereas
>>  the other delivers "25" should be made clear in the document,
>
>I do not agree that any of the idioms are delivering

I want to know what 'delivering' means. Otherwise this discussion is 
just spiralling into nowhere.

>"25". A given
>property may have a value that is the literal node "25", but the *idioms*
>deliver datatyped literal pairings (or are incomplete and underdefined).
>The idioms are more than just the property value node in isolation.
>
>At the level of the MT, a property may have either a literal node
>denoting a lexical form or a non-literal node denoting a value, to which
>is attached a literal node denoting the lexical form.

Right.

>But all idioms
>produce the equivalent datatyping interpretation -- which is a datatyped
>literal pairing.

Well, no. That is, in some sense the graphs do 'pair' a datatype with 
a literal: but speaking exactly, all the meanings in the idioms are 
determined by the constraints imposed on datatyping interpretations, 
and those have nodes denoting strings and maybe nodes denoting 
values, and maybe some arc labels with extensions which are datatype 
mappings (inverted), and that is all. Nothing in the graph denotes a 
"pairing", and there are no "pairings" in the universes of any 
interpretation.

>It does appear that the datatyping MT may not fully extend to that
>point, and perhaps it should. Pat?
>
>The example above of an RDF API that provides access at the level of
>the datatyping interpretation is, I think, useful here. It would never
>just return a property value of "25".

Well, it MIGHT. But in any case, so what? We aren't talking about 
APIs, we are talking about meanings. We havnt got a standard RDF API, 
so we neednt worry about it.

>It would return a datatyped
>literal pairing

I agree that would be a sensible design for an API in this case. BUt 
I also think that is irrelevant.

Pat


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Received on Monday, 15 April 2002 16:33:16 EDT

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