Suppose that U-Haul decided to begin renting a new kind of truck called MightyMover. The user would add a new subclass of truck, and EXPECT would immediately request the following:
E1--I need to know the capacity of a MightyMover.
The reason for this request is that EXPECT has detected that the capacity of rental equipment is a role that is used during the course of problem solving, specifically while achieving the goal of checking the CapacityConstraint with the method shown in Figure 2. This corresponds to errors of type e5 in Table 1. While many roles may have been defined for the class truck (such as make and year), EXPECT will only request the information that is actually needed for problem solving. The next section illustrates that if any problem-solving method changes and other information is used, then EXPECT will request information according to the changes made.
SALT does not provide support in acquiring this kind of domain-specific factual knowledge. As we mentioned in Section 2.2, this capability would be very useful to maintain product knowledge in configuration systems.