CODEWITHSUNDEEP
xmlxsdxsd-validationxml-validation
eladidan
eladidan

Reputation: 2644

xsd: attribute points to element id

I have an xml describing vertices on a directed graph:

<graph>
  <vertex id="a">
    <edge target="b"/>
  </vertex>
  <vertex id="b"/>
</graph>

Given the schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xs:complexType name="vertex">
    <xs:sequence>
      <xs:element type="edge" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
    <xs:attribute name="id" use="required" type="xs:string"/>
  </xs:complexType>

  <xs:complexType name="edge">
    <xs:attribute name="target" use="required"/>
  </xs:complexType>

  <xs:complexType name="graph">
    <xs:sequence>
      <xs:element name="vertex" type="vertex" minOccurs="0" maxOccurs="unbounded"/>
    </xs:sequence>
  </xs:complexType>
  <xs:element name="graph" type="graph"/>
</xs:schema>

How can I modify the target attribute so it's value can only be valid vertex id's?

so my initial example is a valid xml but: 

<graph>
  <vertex id="a">
    <edge target="c"/>
  </vertex>
  <vertex id="b"/>
</graph>

is not.

Upvotes: 1

Views: 151

Answers (1)

Ian Roberts
Ian Roberts

Reputation: 122414

You can do this with a key/keyref pair. Define them at the graph level, to enforce that the vertex IDs are unique:

<xs:element name="graph" type="graph">
  <xs:key name="vertexKey">
    <xs:selector xpath="vertex" />
    <xs:field xpath="@id" />
  </xs:key>
  <xs:keyref name="edgeRef" refer="vertexKey">
    <xs:selector xpath="vertex/edge" />
    <xs:field xpath="@target" />
  </xs:keyref>    
</xs:element>

Importantly, you also need to add a type to the target attribute of edge, as the types of the key and the reference must be compatible:

<xs:complexType name="edge">
  <xs:attribute name="target" type="xs:string" use="required"/>
</xs:complexType>

(additionally the edge element under the vertex type is missing a name, but I presume this is a copy/paste mistake as the validator would have complained more loudly if your real schema were like that)

Upvotes: 3

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