For a shopping process with two forms, which configuration ensures calculations only occur when the second form is reached?

The selection of backward chaining for taxes and grand total is significant in this context because backward chaining allows for calculations to only be performed once the necessary conditions have been established—in this case, when the second form of the shopping process is reached. By utilizing backward chaining, the calculations for taxes and the total price will be triggered at the point of need, ensuring that they are based on complete and current data input from the customer.

This approach prevents premature calculations and avoids the computational inefficiencies that can arise from calculating totals based on incomplete data, which would happen if the calculations were set to occur trigger-based without the validation of data from the second form. This method aligns with a more efficient processing style in scenarios where user input is sequential and dependent on previous steps, emphasizing the importance of context in triggering calculations.

In contrast, forward chaining would trigger calculations proactively based on data inputs that may not yet be complete, leading to less reliable totals prior to reaching the second form. The other options involving backward and forward chaining for item totals follow a similar rationale regarding when and how calculations are applied based on user inputs.