This presentation is part of the Declarative Expressions Self-Study Course.
Let’s look at the conditional display of a Volume property. If the Volume property is displayed, the expression for the calculation of its value fires – backward chaining.
If the harness does not display Volume (set by a When rule), calculation is not necessary and valuable system resources are saved as a result.
Just imagine if the retrieval and calculation processing of this data had a cost, either literally or just in terms of time and system resources. With a procedural design model you would have to either code a lot of if/else statements to micro manage things, or waste valuable time and money processing data needlessly.
For more information on backward chaining, refer to PDN and Developer Help topics on Locate Pages, Locate Activities and Declare Pages, as well as the e-Learning course on Declarative Pages.