W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > December 2002

Re: datatyping

From: Jos De_Roo <jos.deroo.jd@belgium.agfa.com>
Date: Wed, 4 Dec 2002 01:25:01 +0100
To: "pat hayes <phayes" <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org, w3c-rdfcore-wg-request@w3.org
Message-ID: <OFB7764C4A.59A5B8FA-ONC1256C85.0001E5AB-C1256C85.00024A70@agfa.be>


I think it is worthwhile to take that approach
and then indeed find that

_:x xsd:lessThan "10"^^xsd:integer .
_:x xsd:moreThan "12"^^xsd:integer .
_:x rdf:type xsd:integer .

can not be entailed

-- ,
Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/


                                                                                                                        
                    pat hayes                                                                                           
                    <phayes@ai.uwf.edu>       To:     w3c-rdfcore-wg@w3.org                                             
                    Sent by:                  cc:                                                                       
                    w3c-rdfcore-wg-requ       Subject:     datatyping                                                   
                    est@w3.org                                                                                          
                                                                                                                        
                                                                                                                        
                    2002-12-03 07:47 PM                                                                                 
                                                                                                                        
                                                                                                                        





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.

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.
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 conditions.
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 .

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?

Pat

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Received on Tuesday, 3 December 2002 19:25:37 EST

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