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Re: datatyping

From: Graham Klyne <GK@NineByNine.org>
Date: Wed, 04 Dec 2002 10:34:51 +0000
Message-Id: <>
To: pat hayes <phayes@ai.uwf.edu>
Cc: RDF core WG <w3c-rdfcore-wg@w3.org>

At 12:47 PM 12/3/02 -0600, you wrote:

>Let me summarize a proposal for exactly what we should say about datatypes.
>1. A datatype is assumed to be identified by a uriref. The assertion
>aaa rdf:type rdfs:Datatype .
>is intended to be interpreted by a datatype-savvy RDF engine as an 
>indication that aaa is the uriref of a datatype, and that it is 
>appropriate to attempt to access the information associated with that 
>datatype. The exact form in which this information is to be provided to an 
>RDF engine should be specified as part of the API of any such engine.

Or may be built-in to the engine?  (Technically, I think that's covered by 
your description, but I think a casual reading might overlook this.)

>Such an assertion does not constitute a definition of a datatype. There is 
>no way to define a datatype in RDFS. Datatypes are defined externally to RDFS.
>2. In order to be useful, some information  about a datatype needs to be 
>provided to a datatype-savvy RDF engine. The information is of various 
>kinds, and some datatypes may provide only part of the information. 
>Insofar as information about the datatype is unavailable, a datatype-savvy 
>RDF engine will be able to draw only the same conclusions as a 
>non-datatype-savvy RDF engine. Or, if you like, stated semantically, 
>datatype entailment is defined relative to the information provided by the 
>datatype information source. If you get more information, you can make 
>more inferences; if you get none, then the datatype adds nothing and you 
>are just doing RDFS. That way, RDFS entailment is like datatype entailment 
>with an empty-information datatype.
>3a. The minimal kind of information is a specification of which literals 
>are syntactically correct, ie in the lexical space of the datatype, and 
>which are not.
>This information being unobtainable for a resource which is asserted to be 
>in the class rdfs:Datatype may be considered an error condition.

Or may render the assertion meaningless?

>3b. The second kind of information is a specification of which literals 
>map to the same value in the datatype. This information can be 
>conceptualized as a set of equations between typed literals with the same type:
>"aaa"^^ddd = "bbb"^^ddd .
>but it may also be provided, for example, by giving a mapping from lexical 
>forms to canonical lexical forms.
>3c. The third kind of information is like 3b, but specifies identities 
>between forms under different datatypes:
>"aaa"^^ddd = "bbb"^^eee .
>This may be provided, for example, by giving schematic mappings between 
>canonical lexical forms of the different datatypes under various boundary 
>3d. The fourth kind of information is subset relationships between value 
>spaces of different datatypes. This can be specified directly by RDFS 
>subclass assertions of the form
>ddd rdfs:subClassOf eee .

Isn't 3d technically implied by 3a-3c?   Do you mean that 3d could be 
provided without 3b/3c?

The rest looks sensible to me.


>Information of type 3a enable inferences of the form
>aaa ppp "xxx"^^ddd .
>aaa ppp _:x
>_:x rdf:type ddd .
>and hence is often sufficient to detect datatype clashes
>Information of types 3b enables inferences of the form
>aaa ppp "xxx"^^ddd .
>aaa ppp "yyy"^^ddd .
>Information of type 3c enables inferences of the form
>aaa ppp "xxx"^^ddd .
>aaa ppp "yyy"^^eee .
>Information of type 3d allows RDFS class reasoning to support inferences 
>of the form
>aaa ppp "xxx"^^ddd .
>aaa ppp _:z .
>_:z rdf:type eee .
>Is that OK?
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Graham Klyne
Received on Wednesday, 4 December 2002 05:55:38 UTC

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