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Inclusion and extension

DSD descriptions can consist of several XML documents that can be combined using import.

This makes it easy to

Example:

Assuming basic.dsd contains: 

<dsd xmlns="http://www.brics.dk/DSD/2.0"
     xmlns:p="http://www.example.org/basic">

  <if><element name="p:widget"/>
    <declare>
      <contents>
        <repeat><element name="p:thingy"/></repeat>
      </contents>
      <attribute name="type"/>
    </declare>
  </if>
  ...
</dsd>

then we may use this schema in another schema: 

...
<import href="basic.dsd"/>

<if>
  <and>
    <element name="p:widget"/>
    <attribute name="type"><string value="small"/></attribute>
  </and>

  <require><contents>
    <repeat max="7"><element name="p:thingy"/></repeat>
  </contents></require>
  <declare>
    <attribute name="style"/>
  </declare>
</if>
...

which means that a widget with type="small" can at most have 7 thingy child elements (restricting the basic definition), but additionally, it may have a style attribute (extending the basic definition).

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