Intelligent Systems for Engineers and Scientists

ion links and index linksThe classes may form a structured hierarchy, in which the different levelscorrespond to the level of detail of the case descriptions. Riesbeck and Schank[5] distinguish two types of link between classes and their specializations:abstraction links and index links. A subclass connected by an abstraction linkprovides additional detail to its superclass, without overriding any information.An index link is a specialization in which the subclass has an attribute valuethat is different from the default defined in its superclass. For example, theclass Refrigerator_faultmight have an index link to the classElectrical_fault, whose defaults relate to faults in vacuum cleaners(Figure 6.3(a)). Suppose that we wish to save an instance of fixing a refrigerator, wherethe refrigerator exhibited the following symptoms: • failed to chill food;• made no noise;• the light would not come on. This case might be stored as an instance of the class Refrigeratorfault,which, as already noted, has an index link to the class Electricalfault.Domestic_equipment_fault Repairable_faultCatastrophic_fault Refrigerator_faultWashing_machine_faultToaster_faultElectrical_fault Mechanical_fault Plumbing_fault Abstraction linksIndex links(a)ion linksIndex links(a) fitting newbearings removingcompressor housingfixing a noisyrefrigeratorfixing a noisywashing machinecase where replacementmotor caused electricalinterferenceMotor_fault