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RE: ACTION 2001-11-02#02: Datatyping use-cases from CC/PP

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Thu, 8 Nov 2001 18:28:39 -0600
Message-Id: <p0510101ab810cff7ae7c@[65.212.118.147]>
To: Patrick.Stickler@nokia.com
Cc: w3c-rdfcore-wg@w3.org
>  > -----Original Message-----
>>  From: ext Brian McBride [mailto:bwm@hplb.hpl.hp.com]
>>  Sent: 07 November, 2001 14:43
>>  To: Stickler Patrick (NRC/Tampere)
>>  Cc: phayes@ai.uwf.edu; w3c-rdfcore-wg@w3.org
>>  Subject: Re: ACTION 2001-11-02#02: Datatyping use-cases from CC/PP
>>
>>
>>
>>
>>  Patrick.Stickler@nokia.com wrote:
>>  [...]
>>
>>
>>  >>
>>  >
>>  > Well, I'm presuming that if no rdfs:subClassOf statements
>>  > were encountered which define that relation prior to
>>  > testing the range constraint, that one could not know for
>>  > sure that the type absolutely was not a subtype, ever,
>>  > but insofar as the knowledge present at hand, it would not
>>  > be and the test of the constraint should fail.
>>
>>
>>  Or you could just infer that the value must be of that type as well.
>
>Danger. Danger.
>
>One might, but not in any *commercial* system where data
>integrity is paramount. I want to *know* that the value
>is a decimal encoding of an integer before I treat it as
>such. If it might be hexidecimal, or even binary (e.g.
>"10101010" what is it, decimal or binary?) I'm not going
>to use it.

Ah, I begin to understand. Right, you had better not USE it anywhere 
that depends on the actual value, if you have no way to know what the 
value is. But RDF doesn't 'use' data in this way; it just provides a 
way to store, transport and combine information so as to be able to 
draw some conclusions and keep the integrity of the data intact. 
Often, information will be incomplete. However, if you can 
characterize what information it is that you require in order to be 
able to 'use' something, then RDF can either supply it or tell you 
that some part of it is unavailable at present. But being unavailable 
does not mean being false.

>And if I don't have enough information to know what it is
>or should be, then that's equivalent to being invalid. No?

No, definitely not.

>Or at the very least "undefined".

Sure, but that is very different from "invalid". Please don't get 
these mixed up. If I may use a metaphor, you want something to be on 
an exact mark. Undefined means below the mark, invalid means above 
the mark. They are both off the mark; but the difference is 
important, since inference can only go one way. If information is 
incomplete, there is a hope of its getting to the mark in the future. 
If it is invalid, there is no hope at all. The difference matters.

>
>>  Validation is kinda tricky in RDFS.  If I understand it
>>  correctly, RDFS has no
>>  means of expressing negation, so can't express a contradiction.
>>
>>  You can define validation to mean that there is specific
>>  confirmation that all
>>  domain and range constraints are met.  I guess that is what
>>  you had in mind.
>
>Yes.
>
>>  RDFS does not currently define any concept of validation.
>
>Perhaps not a formal one, no, but hopefully one can test,
>at any given point in time, if all constraints for a given
>subgraph are satisfied.

What are the "constraints for a given subgraph"? (For that matter, 
what are the "constraints" for anything in RDF? I don't recall this 
concept of "constraint" ever arising previously.)

>Otherwise, what's the point of
>defining constraints?

Patrick, you are the only person who ever mentions 'constraints'. You 
seem to be inhabiting a different universe than the rest of us. Tell 
you what: let us all agree to not talk of 'constraints', and not to 
use the words 'prescriptive' or 'normative'. Then questions like the 
above do not arise, and we can all get by with a lot fewer emails.

Pat
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Received on Thursday, 8 November 2001 19:28:30 EST

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