Inheriting Well-formed Formulae in a Formula-Agumented Semantic Network

We examine a commercial application, a large portion of whose domain knowledge is taxonomic in nature, and investigate the suit-ability of inheritance networks for the task of reasoning about knowledge in this area. We claim that standard inheritance networks are not suuciently expressive to capture domain knowledge, and introduce formula-augmented semantic networks (FANs), a semantic network which attaches well-formed formulae to nodes. We investigate the concept of inheriting wws in such a network and give a method for computing the sets of well-formed formulae that apply to a given node. Finally, we compare FANs to more familar knowledge structures and the task of inheriting wws to more familar concepts such as reasoning about sets of default rules in non-monotonic systems. Inheritance has long been recognized as useful in business domains. This paper investigates the suitability of inheritance networks for reasoning about beneets in the medical insurance domain. The goal has been to develop an expert system that can answer customers' questions about their insurance beneets. Customers typically ask whether a particular service | such as a hip replacement or a CAT scan | is covered, and what restrictions and limitations apply to this coverage (e.g., deductible, maximum number of services per beneet period). Because so much of the information about medical services is taxonomic in nature | e.g., spinal manipulation is a type of physical therapy; physical therapy, speech therapy, and occupational therapy are all types of therapy | and because coverage and accompanying restrictions are to a large extent inherited along these taxonomic lines, it is natural to encode much of this information in an inheritance network. On the other hand, a signiicant chunk of information is in the nature of complex business rules specifying certain restrictions that cannot easily be mapped into a network structure. For example, rules such as The initial newborn exam must be performed during the mother's hospitalization for delivery and If a patient has exceeded the substance abuse beneets for the year, payment for hospitalization charges may be made under the patient's inpatient hospital beneet do not map into class-subclass or class-attribute links. Instead, it seems more natural to regard such rules as well-formed formulae, and to reason directly with such wws. To accomplish this, we introduce an extension of inheritance networks which we call formula-augmented semantic networks or formula-augmented inheritance networks (FANs). A FAN looks much like an inheritance network, except that a …