openVALIDATION provides various functions. Let's say we want to check in a rule whether we have spent more money on shopping than our budget allows.

We have the following scheme:

    - article : text
      price : 0

And here's the rule that goes with it:

SUM OF shopping_list.price
    AS expenses

the expenses MUST NOT EXCEED the budget of 20 €.

First, we define a variable called Expenses. This variable uses the SUM OF function. The list of all prices from the shopping list is transferred to the function. The function SUM OF calculates a sum and thus has a return value of type Number. The Issues variable is automatically assigned this data type and can then be used within the rule.

The rule itself contains a numeric comparison operation. The whole thing looks like this:

var expenses = sum( -> a.price))

If (expenses > 20 )
   throw Error("the expenses MUST NOT EXCEED the budget of 20 €")

Functions can of course also be used within a rule.

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