Universal attachment: an integration method for logic hybrids
Karen L. Myers · Principles of Knowledge Representation and Reasoning · 1991
Hybrid representation systems have proven to be essential for successful knowledge-based problem solving. Logic hybrids, which contain a representation component based on axiomatic representations and deduction, comprise a particularly important subclass of hybrid systems. In this dissertation, we present the integration method of universal attachment for use in constructing logic hybrids. Universal attachment is based on links, referred to themselves as universal attachments, that connect expressions in a logic to programs and data in arbitrary representation languages. Deduction serves as the primary reasoning mechanism in universal attachment systems. However, when expressions with attachments are encountered during the inference process, the corresponding attached data and programs are used to directly evaluate those expressions. Universal attachment has several advantages over other attachment-based integration methods, including greater expressiveness and modularity. Universal attachment is defined formally as an inference rule in an extended logical framework and is shown to satisfy an appropriate condition of soundness. The completeness of the rule is established for first-order theories on the condition that the set of attachments in use satisfies a simple closure constraint. In contrast, other attachment methods are shown to be inherently incomplete. The dissertation also addresses more practical issues related to the use of logic hybrids. A set of policies is presented that provide guidance in exploiting the expanded representational and inferential capabilities of logic hybrids. These policies are based on experimental results obtained using an implemented universal attachment system. A procedure for automatically generating universal attachments is also defined. The procedure uses an extension of logic compilation techniques to produce new programs and attachments to those programs from a base set of previously defined attachments and programs. It is shown that the generation procedure can produce sizable collections of useful attachments and as such is a valuable specification tool for users of attachment systems.