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X3D-related comments on Schema datatypes

From: Don Brutzman <brutzman@nps.navy.mil>
Date: Fri, 12 May 2000 20:35:59 -0700
Message-ID: <391CCD9F.B5E7517D@nps.navy.mil>
To: www-xml-schema-comments@w3.org
CC: X3D Contributors <x3d-contributors@web3d.org>
The following comments are based on document review and known DTD
shortfalls.  We have only done preliminary examinations of schema
instantiations for the X3D tagset.  Summary:  looks good.

References:
http://www.web3D.org/x3d.html
http://www.web3D.org/technicalinfo/specifications/vrml97/part1/fieldsRef.html
http://www.w3.org/TR/xmlschema-0/
http://www.w3.org/TR/xmlschema-1/
http://www.w3.org/TR/xmlschema-2

1.  The Extensible 3D (X3D) specification makes heavy use of float, double
and integer lists.  The list support for float/double/integer appears
useful and usable.

2.  X3D lists of floats/doubles/integers are often lists of 2-tuples, 
3-tuples or 4-tuples.  Such typing is commonplace for 3D graphics 
(e.g. translations are 3-tuples, orientations are axis-angle 4-tuples).
Regular-expression patterns will let us express these relationships
(hopefully without redefining the numeric base types, not yet sure).
No draft schema appears in the current SVG draft - pertinent examples 
are welcome.

A helpful facet might be to specify the tuple-ordinality of a list type,
so that only appropriate multiples of the typed data are allowed.  Please 
be aware that wrapping such X3D tuples in their own type tags has been 
considered, but is impractical due to unneccesary redundancy and the 
extremely large volumes of numeric data involved in many scenes.
 
3.  A further feature X3D might use is the ability to identify & evaluate
further numerical constraints to be placed on data.  For example, Normal 
(i.e. perpendicular vector) 3-tuples should have unit magnitude.  It 
appears language-specific data validation will be needed to check such 
cases, probably corresponding to named simpleType or complexType 
definitions.  So Schema capabilities at least appear sufficient to
enable such checking independently, even if not supporting it directly.

4.  Thanks for this excellent work.  If further issues are identified
during eventual production of the X3D schema, we'll report them back.

all the best, Don
-- 
Don Brutzman  Naval Postgraduate School, Code UW/Br Root 200  work 831.656.2149
              Monterey California 93943-5000 USA              fax  831.656.3679
Virtual worlds/underwater robots/Internet     http://web.nps.navy.mil/~brutzman
Received on Friday, 12 May 2000 23:33:16 UTC

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