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Re: Input sought on datatyping tradeoff

From: Bob MacGregor <macgregor@ISI.EDU>
Date: Thu, 25 Jul 2002 21:21:14 -0700
Message-ID: <009201c2345b$eed65f50$6601a8c0@STRIKER>
To: <bwm@hplb.hpl.hp.com>
Cc: <www-rdf-interest@w3.org>

My original reaction was that the answer to case D should be yes, but that
many people and implementations would likely choose yes for A as well.

However, the mention of non-monotonicity raised a red
flag for me.  Consider a slightly different pair of cases:

Test A3:

   <Jenny> <ageInYears>   "10" .
   <Film>  <title>        "10" .

Test D3:

   <Jenny>  <ageInYears> "10" .
   <ageInYears> rdfs:range xsd:decimal .
   <Film>  <title>  "10" .
   <title> rdfs:range xsd:string .

My feeling is that the two "tens" in D3 must be considered
unequal, since the ranges of the two properties are disjoint.
Monotonicity then dictates that the same answer must apply
to A3.  Hence A should be "No".

- Bob

----- Original Message ----- 
> Date: Thu, 11 Jul 2002 19:46:49 +0100
> To: www-rdf-interest@w3.org
> From: Brian McBride <bwm@hplb.hpl.hp.com>
> Subject: Input sought on datatyping tradeoff
> 
> 
> 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.  Please can we have all responses by 26th July 
> 2002.  Questions and discussion should take place on this list.
> 
> INTRODUCTION TO DATATYPES
> =========================
> 
> Let's explain the basic ideas behind our approach to datatyping.  The aim 
> is to define how datatype values, e.g. integers, dates etc should be 
> represented in RDF.  We are building on the XML Schema datatypes 
> specification.
> 
> It is important in getting the semantics correct that we distinguish 
> between a datatype value, e.g. the integer 10 and a lexical representation 
> of the value, e.g. the string "10".
> 
> 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 the string "10".
> 
> This idiom treats an XML schema 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?
> 
> There are variations on this test which should be considered before answering.
> 
> Test A2:
> 
>    <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 A3:
> 
>    <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.
> 
> The answer must be the same for all three of these A tests.
> 
> These test cases only relates to the situation where there are no range 
> constraints on the properties.
> 
> Now for a different kind of test.  How do the values of the two idioms relate?
> 
> 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 Tests A and Test D both be 
> yes.  Either the A's can be yes or D can be yes, but not both.  We have to 
> decide which of these is the most important to have.
> 
> 
> WHY THESE TEST CASES MATTER
> ===========================
> 
> The formal semantics can define the meaning of a literal in one of two 
> ways, given:
> 
>    <Jenny> <ageInYears> "10" .
> 
>    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 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 (by 26 July 
> 2002) indicating whether you believe its more important to have the answer 
> to test cases A be yes, or test case D be yes:
> 
>    Test A:
> 
>    <Jenny> <ageInYears> "10" .
>    <John>  <ageInYears> "10" .
> 
> Test D:
> 
>    <Jenny>      <ageInYears> "10" .
>    <ageInYears> <rdfs:range> <xsdr: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
> 
===========================================
Bob MacGregor                                   macgregor@isi.edu
Project Leader                                     voice: 310.448.8423
Distributed Scalable Systems Division   cell: 310.251.8488
University of Southern California            fax: 310.822.6592
Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Received on Friday, 26 July 2002 00:26:38 GMT

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