declarative expression
Declarative expressions help you configure your application to automatically update property values. By setting up declarative expressions, you define a computational relationship between properties.
For example, you can define the total order amount as the sum of all line items. The following figure shows a sample declare expression.
Whenever the input values change, the declarative process automatically updates related property values. In this example, when a customer adds a new item to the shopping cart, the order amount increases automatically.