XPath Expressions

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Expressions are used within constraints to generate a value that is true.

There are three types of expressions usable for constraints:

  • Comparisons with operators
  • Functions
  • Exist-expressions


A comparison expression consists of two attributes or values, separated by a comparison operator, like ‘=’, ‘<=’ and ‘>’.


See this page for information on the available functions.

Exist Expressions

The last type of expression, the exist expression, can be used to check whether a specific association is filled or not.