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b*c*b*c* vs. (b*c*)^2,2

From: Torsten Grust <Torsten.Grust@uni-konstanz.de>
Date: Thu, 12 Feb 2004 10:39:52 +0100
Message-ID: <16427.18920.698381.323704@gargle.gargle.HOWL>
To: xmlschema-dev@w3.org

G'day all,

  I would be very grateful if anybode could enlighten me on the
following ambiguity issue.

The following declaration for element a is clearly ambigious (and XSV
2.6-2 complains accordingly):

  <xs:element name="a">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="b" type="xs:integer"
                    minOccurs="0" maxOccurs="unbounded"/>
        <xs:element name="c" type="xs:integer"
                    minOccurs="0" maxOccurs="unbounded"/>
        <xs:element name="b" type="xs:integer"
                    minOccurs="0" maxOccurs="unbounded"/>
        <xs:element name="c" type="xs:integer"
                    minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

The content model for element a essentially is b*c*b*c*.

If I rephrase the schema as follows, the content model language for
element a does not change and---surprisingly to me---there is no
ambiguity issue anymore according to XSV:

  <xs:element name="a">
    <xs:complexType>
      <xs:sequence minOccurs="2" maxOccurs="2">
        <xs:element name="b" type="xs:integer"
                    minOccurs="0" maxOccurs="unbounded"/>
        <xs:element name="c" type="xs:integer"
                    minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

The content model now is (b*c*)^2,2 (where r^n,m represents an n-fold minimum
and m-fold maximum occurence of r).

I fail to see how this reformulation resolves the ambiguity.  I would
greatly appreciate any insight on this.

Best wishes and thank you,
   --Torsten

--
  | Dr. Torsten Grust                          Torsten.Grust@uni-konstanz.de |
  |                                   http://www.inf.uni-konstanz.de/~grust/ |
  | Database Research Group, University of Konstanz (Lake Constance/Germany) |
  |             (Please avoid sending me MS Word or PowerPoint attachments.) |
Received on Thursday, 12 February 2004 04:39:54 GMT

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