HYPO is a computer program, an expert system, that models reasoning with cases and hypotheticals in the legal domain.
It is the first of its kind and the most sophisticated of the case-based legal reasoners, which was designed by Kevin Ashley for his Ph.D dissertation in 1987 at the University of Massachusetts Amherst under the supervision of Edwina Rissland.
HYPO's design represents a hybrid generalization/comparative evaluation method appropriate for a domain with a weak analytical theory and applies to tasks that rarely involve just one right answer.
Since Anglo-American common law operates under the doctrine of precedent, the definitive way of interpreting problems is of necessity and case-based.
Rissland and Ashley (1987) envisioned HYPO as employing the key tasks performed by lawyers when analyzing case law for precedence to generate arguments for the prosecution or the defence.
[3] HYPO was a successful example of a general category of legal expert systems (LESs), it applies artificial intelligence (A.I.)
[4] As noted by Ashley and Rissland (1988) CBR is used to "... capture expertise in domains where rules are ill-defined, incomplete or inconsistent".
The CKB contains HYPO's base of known cases that are highly structured objects and sub-objects both real and hypothetical in the area of trade secret law.
At this point the fact gathered module may request additional information from the user in order to draw a legal conclusion.
[15] The quality of HYPO's results speak for themselves, in that a number of sequent legal reasoning systems are either directly based upon HYPO's mechanisms as in the case of Kowalski (1991),[16] TAX-HYPO, precedent case-based system operating in the statutory domain of tax law (Rissland and Skalak 1989), CABARET, a mixed-paradigm cases and rule system for the income tax law domain, (Skalak and Rissland 1992), CATO, IBP, developed for argumentation to make predictions based on argumentation concepts (Brüninghaus and Ashley 2003), or their creators at least pay homage to HYPO in their discussions (Henderson and Bench-Capon 2001[17]).