XML Schema part 2 -Datatypes

We are using a similar type system (derived primarily from the DCD technical note)
in a number of our products. We use XML metadata for a somewhat different purpose
than XML Schema is designed for - we are primarily interested in supporting
object-oriented modeling of business objects. These objects may be realized in
various forms: e.g. as rows in a database table, as messages travelling through
a network, or possibly as XML. Our focus is therefore not so much on specifying
and validating the string representation of types in XML - we are more interested
in having a robust, general type system that can be applied in various contexts.

Still, we have hit many issues that XML Schema addresses, so I'm sending the
following comments.

1. The text of ISO 8601 is quite imprecise in many areas. There is a draft
2nd edition of ISO 8601 available from http://www.cl.cam.ac.uk/~mgk25/8601v04.pdf
which tighens up and clarifies much of the language.

2. As you probably know, ISO 8601 has a very wide range of allowable formats with
many permissible variations. I would recommend specifying a subset of ISO 8601
for use with XML Schema. We have made the following simplifications, for example:

   a. Dates and times are in "extended format" only, e.g. 1999-05-27, not 19990527;
       23:03:27, not 230327.
   c. Commas are not permitted as "decimal point" indicators.
   d. None of the "truncated representations" are permissible (e.g. "-05-27" for a date).
   e. Our "interval" data type only allows the "period of time" representation, for
       example "P2DT10H20M6.6S".

These may be too restrictive; but I still think ISO 8601 (1988) is too imprecise and
permissive to be a good standard by itself.

3. We use the types "i1", "i2", 'i4", "i8", "ui1", "ui2", "ui4", "ui8" for signed and unsigned 
integers of sizes 1, 2, 4, and 8 bytes. Also "r4" and "r8" for 4- and 8-byte reals.
I think these were in DCD. It appears you have a more general integer type 
system, but it would be nice to have these specific types predefined.


Jon Dart                               jdart@tibco.com
TIBCO Software Inc.              650-846-5099

Received on Wednesday, 26 May 1999 16:49:14 UTC