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Re: SV: fixed attribute in a xsd mapping schema?

From: Jeni Tennison <jeni@jenitennison.com>
Date: Wed, 9 Jul 2003 11:04:51 +0100
Message-ID: <80171748841.20030709110451@jenitennison.com>
To: Tomas.Oberg@partnertech.se
CC: xmlschema-dev@w3.org

Hi Tomas,

> I use the two tables Contents and ColumnNames to store data in SQL
> Server 2000. Every Contents instance points to a ColumnNames
> instance. But I don't have any control of what datatype I store in
> the Contents table. That's why I would like to be able to use
> different datatypes of the Content element according to which
> ColumnName the Content points to.

In XML terms, then, you want to have:

  <Content ContentID="1" Content="1" ColumnNameID="1"
           ColumnName="ColumnName1" />
  <Content ContentID="2" Content="foo" ColumnNameID="2"
           ColumnName="ColumnName2" />

and you want to say that the Content attribute of the first <Content>
element is of type xs:int and the Content attribute of the second
<Content> element is of type xs:string.

The only way you can arrange this co-occurrence constraint using XML
Schema is to add an xsi:type attribute that controls the type of the
Content attribute. Your instance would look like:

  <Content ContentID="1" Content="1" ColumnNameID="1"
           ColumnName="ColumnName1" xsi:type="ColumnName1" />
  <Content ContentID="2" Content="foo" ColumnNameID="2"
           ColumnName="ColumnName2" xsi:type="ColumnName2" />

Alternatively, you can create a transformation that takes your
document and converts it into:

  <ColumnName1 ContentID="1" Content="1" ColumnNameID="1" />
  <ColumnName2 ContentID="2" Content="foo" ColumnNameID="2" />

An XML Schema schema can declare the elements <ColumnName1> and
<ColumnName2> with different types.

Or you could switch to using RELAX NG instead, in which the
co-occurrence constraint can be expressed very easily:

  <element name="Content">
    <attribute name="ContentID"><data type="int" /></attribute>
    <attribute name="ColumnNameID"><data type="int" /></attribute>
    <choice>
      <group>
        <attribute name="ColumnName">
          <value>ColumnName1</value>
        </attribute>
        <attribute name="Content"><data type="int" /></attribute>
      </group>
      <group>
        <attribute name="ColumnName">
          <value>ColumnName2</value>
        </attribute>
        <attribute name="Content"><data type="string" /></attribute>
      </group>
      ...
    </choice>
  </element>

Let us know which alternative you want to investigate if you need
further help with it.
  
Cheers,

Jeni

---
Jeni Tennison
http://www.jenitennison.com/
Received on Wednesday, 9 July 2003 06:04:58 GMT

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