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Re: General comments on XSCH Datatypes note

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Tue, 25 Jan 2005 17:10:44 +0000
Message-ID: <41F67D94.7090407@hplb.hpl.hp.com>
To: Jeff Pan <pan@cs.man.ac.uk>
CC: "www-archive@w3.org" <www-archive@w3.org>


Hi Jeff,


Summary:
- in-line thoughts about Evan's general comments
- action plan???


I've been a bit remiss in not driving forward with this. We're meant to 
have a new version for Thursday.

I think we've basically got the detailed comments dealt with, except for 
actually editing.

I think we don't have to resolve the question between us of how much 
does OWL DL cover user defined datatypes or not (although we should try 
and have a verbal discussion about this, maybe in Boston - I think it 
would be interesting). I think your DL material is relevant whether or 
not OWL already presupposes it (it certainly doesn't adequately document 
it).

Going through Evan's comment in-line:

ewallace@cme.nist.gov wrote:
> My review of "XML Datatypes in RDF and OWL" [1] 
> 
> Overall, this is a good document.  It discusses a number
> of issues related to the use of datatypes in RDF and OWL that were left
> unresolved by the Recommendations.  It is comprehensive in addressing
> the issues discussed: covering alternative approaches and providing
> appropriate references and/or quotes as necessary.  In fact, because
> of this comprehensiveness and the importance of the references,
> reviewing this document was more of a project than I had originally
> envisioned (although reading these references proved enlightening)..  
> 
> I have no major issues with this document, although I do have some
> lesser concerns and comments.  These fall into two categories: general
> and detailed.  The detailed concerns were already presented in an
> email sent to the list yesterday [details].  The general concerns
> follow below.
> 
> 
> * The document covers a number of loosely related subjects.  It is
>   like a bag of datatype issues and other related material.  Different
>   parts will be of interest to different audiences.  I mentioned this
>   before, but my main concern now is that someone reading linearly
>   through the document will encounter the interpretation descriptions
>   in 1.2, 1.3, and 1.4 and stop reading.  



>  I think such material would
>   be better placed as an appendix. 

Really for you to either agree with or argue against.

I tend to agree with Evan and would suggest following changes:

Merge current

0. Intro and 1.1 XML Schema

with

1. Intro

Current text without namespaces stuff

1.1 Structure of this document

Give an indication of the intended reader and role of each section

In particular highlight the role of DL stuff as providing theoretical 
background for the meaning of user-defined datatypes in OWL DL, and role 
of appendix as supplementing material in RDF and OWL Semantics to cover 
this document.

1.2 Namespace declarations

1.3 XML Schema stuff


New appendix

A. (Title?)

A.1  old 1.2
A.2  old 1.3
A.3  old 1.4


>  It was also not clear to me the
>   purpose and role of such material in this document.  By role, I mean
>   are the interpretation descriptions in 1.2 and 1.3 quotes from the
>   RDF and OWL semantics documents respectively or a different form for
>   the same content?
> 

We should add URLs to the respective documents and indicate clearly any 
differences if any.

> * An important reference for datatypes in computing environments is
>   the ISO standard on Language-independent datatypes - ISO/IEC
>   11404:1996.  It provides an excellent framework for describing
>   datatypes and appears to have been a strong influence on the XML
>   Schema base types document [2] (which includes a reference to
>   11404).  The XSCH note could benefit referencing the ISO work
>   directly and using some of its terminology, although I don't think
>   that this is necessary for this iteration of the note.
> 

Suggest we add the reference and a single sentence in the XML Schema 
introductory section.


> * My primary interest in these datatype issues is with the treatment
>   of numeric types being consistent with their use in engineering
>   applications (or at least usable by those applications).  Loss in 
>   precision or unexpected changes in values due to automatic type
>   conversion could be problematic in an engineering environment.
> 
>   Engineering view of some numeric types:
> 
>   To explain the engineering point of view on this, let me mention
>   three important numeric types for that domain: count, measurement,
>   and constant.
> 
>   A count is an integer representing essentially the
>   cardinal number for a set of things classified by some set of tests.
>   An example would be the count of packages of candy available for
>   shipment.  A count is an exact number.  Tests may include
>   measurements, but a count is not an approximation of a sum of 
>   these measurements nor is it a sum of the approximation of these 
>   measurements.
> 
>   A measurement is an inexact numeric value (usually represented as a
>   real) produced by some measurement method.  This value denotes a
>   value range which includes the actual value.  The actual value is
>   unknowable, but more precise measurement methods can reduce the
>   range of uncertainty up to a point.  The precision or uncertainty is
>   usually included with the measurement value.  Either implicitly
>   using significant figures or explicitly using a seperate property
>   value such as error range.
> 
>   A constant is an exact value used in computation.  It may or may not
>   be possible to express exactly as a numeric.  An inch is exactly
>   2.54 centimeters, but Pi is not 3.14159.
> 
>   This suggests some potential needs and concerns for a type system
>   underlaying this.  1. Because the value spaces for these types
>   are different, measurements are disjoint from counts and constants.
>   2.  Some means of capturing precision or error/uncertainty is needed
>   for measurement values. 3. Some means is needed for denoting
>   constants that cannot be expressed precisely in numeric form.
> 
>   Some answers about how 1 and 2 can/must be handled with XML Schema
>   types are revealed in the XML Schema Datatypes document. In [2] the
>   description for Decimal explicitly states that, "Precision is not
>   reflected in this value space, the number 2.0 is not distinct from
>   the number 2.00."  Thus precision cannot be encoded in decimal
>   values or other types derived from or constructed with
>   Decimal. Meaning: that objects must used to state precision or error
>   properties for measurements (this is not a bad approach any since
>   there are often other properties or metadata associated with a
>   measurement as mentioned previously by Bernard [3]).  Measurements
>   on the SW are thus not datatypes and the disjoint type issue becomes
>   mute.
>


At telecon I agreed to draft a new section based on this point, I would 
put it before the appendix. It could be a second appendix, although it 
feels less heavy than typical appendix material.

>   For issue 3, there remains no answer.  As far as I know there is no
>   way to denote a rational value without using a numeric literal, but 
>   many important values cannot be expressed precisely as numeric 
>   literals.
> 
>   Information on these issues may belong in this datatype note or not,
>   I am not sure.  I do think that the SWBPD wg should present these
>   issues in some one of its notes, though.
> 
> -Evan 
> 
> [1] http://www.w3.org/2001/sw/BestPractices/XSCH/xsch-sw/
> [2] http://www.w3.org/TR/xmlxschema-2/
> [3] http://lists.w3.org/Archives/Public/public-swbp-wg/2004Dec/0119.html
> [details] http://lists.w3.org/Archives/Public/public-swbp-wg/2005Jan/0040
> 



I'm happy to have a stab at making all these changes except for changes 
inside your text (other than those precisely described in your e-mail 
response to Evan). The most notable thing I would be missing is links 
into the semantics docs for how the current sections 1.2, 1.3, 1.4 
relate to them. I would leave clear markers where I need your help and 
hopefully have this ready in time ....

Jeremy
Received on Tuesday, 25 January 2005 17:11:16 GMT

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