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RE: <restriction> - Bad Kleene Notation

From: <zongaro@ca.ibm.com>
Date: Wed, 3 Oct 2001 11:52:53 -0400
To: www-xml-schema-comments@w3.org
Message-ID: <OFB6861A18.F8FC0929-ON85256ADA.0056D7B1@torolab.ibm.com>

     I wrote:
     For example, consider a regular set of strings consisting of any 
number of the letters a and b, but at most one instance of each of the 
letters c and d.  One way of specifying this is as follows:


It's much easier to express by saying it has the following form:


with the added restriction that that there is at most one instance of each 
of c and d.

     Another way of describing this language would be as the intersection 
of the languages generated by the following regular expression:

  (a|b|c)*d?(a|b|c)*  and (a|b|d)*c?(a|b|d)*

Of course, I still thinks that's not as clear as (a|b|c|d)* with the 
additional prose restriction.

     If someone has a more concise way of describing this using only 
regular expressions, please jump in.


Henry Zongaro      XML Parsers development
IBM SWS Toronto Lab   Tie Line 969-6044;  Phone (905) 413-6044
Received on Wednesday, 3 October 2001 11:53:00 UTC

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