Composition References

Composition References create parent-child relationships between ElementClasses.

Compositions:

• Can be one or two-directional.
• Create a hierarchy where the owner (parent) contains the target (child).
• Can target ElementClasses from other Ontologies only if there is no Opposite Reference. If the composition is bidirectional, both ElementClasses need to exist in the same Ontology.
• Do not require the target ElementClass to have identifiers.

model/references/Script_parameters.xml

<reference name="parameters">
  <associationType name="composition"/>
  <owner name="Script" ontology="scriptElements"/>
  <target name="ScriptParameter" ontology="scriptElements"/>
  <cardinality>
    <minimum>0</minimum>
    <maximum>*</maximum>
  </cardinality>
  <opposite name="script">
    <cardinality>
      <minimum>1</minimum>
      <maximum>1</maximum>
    </cardinality>
  </opposite>
</reference>

Composition in action

MyScript.xml

<script>
  <parameters>
    <scriptParameter>
      <name>output</name>
    </scriptParameter>
    <scriptParameter>
      <name>log-level</name>
    </scriptParameter>
  </parameters>
</script>

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Single value composition

A Composition Reference can also have a cardinality of 0..1 or 1..1. In this case there is a one-to-one relation between parent and child.

This can be useful in several cases:

• Optional extra behaviour: the child encapsulates some concern that is only activated if the child is defined.
• Reusable behaviour: the same ElementClass is the child in a number of Compositions (without Opposite Reference) and adds some common behaviour.