The Definitions part of a rule gives you finer control over your business rules by letting you set variables at the beginning of your rule.

Variables let you identify and subsequently reference an occurrence of something by a convenient name. Using variables can make your business rules less ambiguous as well as easier to understand. A variable that you define is only valid in the rule in which it is defined.

You define a variable by giving it a name of your choice and then setting this variable to a value. This value can be a number (or even an arithmetic expression), text, or a predefined business term that already appears in your rule (for example, customer). Once you have set a variable, it becomes available in all the parts of the current rule.

To define a constant

The simplest use of Definitions is defining a constant value that you can use throughout your rule. For example, by declaring a variable that you call upgrade value in the following rule, you make the rule easier to understand:

To identify other occurrences of a business term

The Rule Editor defines one variable for each type of business term that it encounters, and identifies it with the word "the". For example, if customer is something you work with in your rules, the Rule Editor will define a variable called the customer, available in your drop-down lists.

If your rule requires you to refer to more than one occurrence of a customer, you have to explicitly define the others in the Definitions part, for example:

To further restrict a variable

You can also use where in the Definitions part to apply further restrictions on the variables that you declare. For example, you could restrict the variable so that it can only be set to valued customers as follows:

Another example shows how to declare the a senior Gold customer variable, initialized to a customer who is a Gold member and at least 65 years old.

Use Definitions with the Else Part

If a rule contains both definitions and a condition part, the Else part of a rule will only be executed if the conditions set in the variables are satisfied and the condition part of the rule is not satisfied.

For example, in the following rule a discount is always applied since any customer will receive at least a 5% discount:

However, if you adjust the rule using the Definitions part, a discount is only applied for customers in the Gold category:

Retrieving all Occurrences of a Business Term

A variable can be used to retrieve a list of all occurrences of a business term. This is done with the ... all instances of construct.

This example creates 3 variables: