Modifying knowledge-based systems (KBSs) is a complex activity that needs to be performed very often. The occurrence of changes in a KBSs environment, requests for extending the system’s functionality, and the debugging of inadequate knowledge are some of the events that demand modifications to a KBSs. One of the difficulties of KBS modifications is that they might require the modification of several related portions of the system. Determining what portions have to be changed and how tochange them requires a deep understanding of how the elements of the KBS interact. This requirement is especially hard for users when the rationale behind the design of a KBS or the details of its implementation are unknown.