Domain-specific operators

The aim of openVALIDATION's grammar is to be as natural as possible. To get even closer to this goal, it is possible to declare domain-specific or semantic operators in the rules.

An example

Schema:

age : 0

{
    age : 0
}

Rule:

the age of the applicant MUST be AT LEAST 18

The rule sounds quite natural, but not quite. The rule could sound much more natural if it were expressed as follows:

the applicant MUST NOT be YOUNGER than 18

That sounds a lot more natural. The problem is that even if openVALIDATION would provide an alias for the operator < called YOUNGER, at the end openVALIDATION does not know which attribute of the schema should be used for the comparison operation. We have to tell openVALIDATION that somehow. We do this by defining a user-defined, domain-specific operator:

 OPERAND Age
OPERATOR SMALLER
      AS YOUNGER
​
the applicant MUST NOT be YOUNGER than 18

We can create a domain-specific comparison operator using a new global element OPERATOR. We can then use this in our rules. In our example, we have created a new comparison operator called YOUNGER. The operator itself consists of a concrete comparison operator, namely LESS or <, and the respective attribute of the schema.

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