HYPO: A Precedent-Based Legal Reasoner

Abstract : In this paper we discuss several key aspects of case-based reasoning ('CBR') and describe how these are handled in our HYPO program which performs legal reasoning in the domain of trade secret law. In particular, we examine the following aspects of HYPO: (1) the structure of a case knowledge base ('CKB'); (2) an indexing scheme ('dimensions ') for retrieval of relevant cases from the CKB; (3) techniques for analyzing a current fact situation; (4) techniques for interpreting and assessing the relevancy of past cases by positioning the current fact situation with respect to relevant existing cases in the CKB as seen from the viewpoint of the case at hand and finding the most-on-point cases; (5) techniques for manipulating cases (e.g., citing, distinguishing, hybridizing); (6) techniques for perturbing the current fact situation to generate hypotheticals that test sensitivity of the current facts to changes, particularly with regard to potentially adverse effects of new damaging facts coming to light and existing favorable ones being discredited; and (7) the use of 3-ply arguments to play out an argument. We then present an extended example of HYPO in action on a sample trade secrets case.