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Re: Draft datatypes message

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Sun, 23 Jun 2002 15:03:02 +0300
To: ext Brian McBride <bwm@hplb.hpl.hp.com>, RDF Core <w3c-rdfcore-wg@w3.org>
Message-ID: <B93B93A6.17364%patrick.stickler@nokia.com>


One additional suggestion:

I think it's enough to restrict the inquiry to only tests C and D.

The tests A and B are less illustrative of the core distinction
between tidy and untidy interpretation of literals, and C and D
will suffice to give users a clear picture of the distinction,
enough (hopefully) to make a choice.

Otherwise, folks could wonder why A can agree with either
interpretation and may get confused about the distinction between
A and B which is minor but makes B seem to be similar to A, etc.

So I recommend that we remove A and B and re-label C and D as
1 and 2 (or T and U) and make the feedback a simple vote
between the two (with optional comments).

Cheers,

Patrick


On 2002-06-21 17:12, "ext Brian McBride" <bwm@hplb.hpl.hp.com> wrote:

> 
> This is first draft of the datatypes message I agreed to produce at the f2f.
> 
> Brian
> =============================================================================
> 
> The RDFCore WG is producing a proposal for how XML Schema datatypes should
> be used in RDF.  We would like some guidance on a particular tradeoff we
> have to make.
> 
> The WG requests that you send your considered answers to
> www-rdf-comment@w3.org, along with any comments, thoughts or questions you
> may have.
> 
> INTRODUCTION TO DATATYPES
> =========================
> 
> Let's explain the basic ideas behind our approach to datatyping.  We are
> proposing two principal idioms for representing datatyped information.  The
> first looks like this:
> 
>  <Jenny> <age>          _:a .
>  _:a     <xsdr:decimal> "10" .
> 
> This can be written in RDF/XML like this.
> 
>  <rdf:Description rdf:about="Jenny">
>    <foo:age xsdr:decimal="10"/>
>  </rdf:Description>
> 
> Here the b-node _:a denotes the integer 10 which can be represented in
> decimal form as "10".  The WG believes that this distinction between
> numbers, e.g. 10 and numerals (which are strings) e.g. "10" is important if
> we are to precisely define the semantics, e.g. 10 # "10".
> 
> This idiom treats an XML datatype as a mapping from a value to a lexical
> representation of the value; this mapping is represented in RDF by a property.
> 
> We believe this idiom to be quite straightforward, but not sufficient on
> its own because it is common practise to write things like:
> 
>  <jenny> <age> "10" .
> 
> where the author of this fragment of RDF means to represent the fact that
> Jenny's age is the number 10.  This is the second idiom, which is where we
> need some guidance.
> 
> 
> SOME TEST CASES
> ===============
> 
> It is here that we need some advice, because we have a choice to make in
> the way we define the formal semantics.
> 
> A few simple test cases:
> 
> Test A:
> 
>  <Jenny> <ageInYears> "10" .
>  <John>  <ageInYears> "10" .
> 
> Should an RDF processor conclude that the value of the ageInYears
> properties for Jenny and John are the same?
> 
> Test B:
> 
>  <Jenny> <ageInYears> "10" .
>  <Jenny> <testScore>  "10" .
> 
> Should an RDF processor conclude that the value of Jenny's ageInYears
> property is the same as the value of Jenny's testScore property?
> 
> Test C:
> 
>  <Jenny> <ageInYears>   "10" .
>  <Film>  <title>        "10" .
> 
> Should an RDF processor conclude that the value of Jenny's age property is
> the same as the value of the Film's title property?  If the value the
> <ageInYears> property is an integer, and the value of the <title> property
> is a string, they are not the same thing and are thus not equal.
> 
> Test D:
> 
>  <Jenny>      <ageInYears> "10" .
>  <ageInYears> <rdfs:range> <xsd:decimal> .
> 
>  <John>  <ageInYears>      _:a .
>  _:a     <xsdr:decimal>   "10" .
> 
> Should an RDF processor conclude that Jenny and John have the same
> age?  [Note: in this example the range constraint is expressed using
> rdfs:range.  We may have to introduce a special datatyping range property,
> but that is an independent detail for now.]
> 
> It is not possible to have the answers to Test B, Test C and Test D all be
> yes.  Either B and C can be yes or D can be yes.  We have to decide which
> of these is the most important to have; (B and C) or D.
> 
> WHY THESE TEST CASES MATTER
> ===========================
> 
> The formal semantics can define the meaning of a literal in one of two ways:
> 
>  tidy) the <ageInYears> property takes a value which is a numeral, i.e. a
> string
> 
>  untidy) the <ageInYears> property takes a value which is some datatype
> value whose string  representation is "10", but without further
> information, such as
> a range constraint, we can't tell exactly what the value is, e.g. the
> string might be in octal.
> 
> If we choose the tidy option, the object of the statement is always a
> string, which means that in:
> 
>  <Jenny> <ageInYears> "10" .
>  <Film>  <title>      "10" .
> 
> the values of the two properties are the same; they are both the STRING "10".
> 
> If we choose the untidy option, the value of the object object of the
> statement is unknown from this statement alone; a range constraint is
> required to determine the value from the literal string:
> 
>  <jenny>      <ageInYears> "10" .
>  <ageInYears> <rdfs:range> <xsd:decimal> .
> 
> With a range constraint, we can know that the object of the property is the
> integer 10.
> 
> CONCLUSION
> ==========
> 
> To end then, please send a message to www-rdf-comments@w3.org indicating
> whether you believe its more important to have the answer to test case B be
> yes, or test case D be yes:
> 
>  Test B:
> 
>  <Jenny> <ageInYears> "10" .
>  <Jenny> <testScore>  "10" .
> 
> Test D:
> 
>  <Jenny>      <ageInYears> "10" .
>  <ageInYears> <rdfs:range> <xsd:decimal> .
> 
>  <John>  <ageInYears>      _:a .
>  _:a     <xsdr:decimal>   "10" .
> 
> 
> We would also like to know the reasons for this preference.
> 
> Brian McBride
> on behalf of the RDFCore WG
> 
> 

--
               
Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Sunday, 23 June 2002 07:58:37 EDT

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