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   XML Schema: regular expression challenge

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  • From: "Roger L. Costello" <costello@mitre.org>
  • To: xml-dev@lists.xml.org
  • Date: Wed, 09 Aug 2000 11:09:58 -0400

Hi Folks,

I am trying to write an XML schema which declares an element, foo, to be
a string, 5-10 characters in length, OR empty.  For example, here are
valid instances of foo:


Here's my attempt at a declaration for foo:

    <element name="foo">
        <simpleType base="string">
            <pattern value="([a-z]|[A-Z]){5,10}|()"/>

In an instance document when I set the content of foo to be empty:


Oracle's schema processor gives me an error.  That either means that

(a) Oracle's schema processor has a bug, or
(b) My regular expression is not correct.

Let's assume that it is the later.  Any suggestions on how else to
express the regular expression?  Note that the following regular
expressions also failed:


As an aside, if an element contains a string of length=0, is that
element "empty"? and thus the element can be expressed as <foo/>?



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