A Multi-Level Organization For Problem Solving Using Many, Diverse, Cooperating Sources Of Knowledge

An organization is presented for implementing solutions to Knowledge-based AI problems. The hypothesize-and-test paradigm is used as the basis for cooperation among many diverse and independent Knowledge sources (KS's). The KS's are assumed individually to be errorfui and incomplete. A uniform and integrated muiti-level structure, the blacKboard. holds the current state of the system. Knowledge sources cooperate by creating, accessing, and modifying elements in the blacKboard, The activation of a KS is data-driven, based on the occurrence of patterns in the blackboard which match templates specified the Knowledge oource. Each level in the blacKboard specifies a different representation of the problem space; the sequence of levels forms a loose hierarchy ir which the element» at each level can approximately be described as abitractions of elements at the ne>.t lower level. This decompostion can be thought of as an a priori frameworK of a plan for solving the problem; ea-h level is a generic stage in the plan. The elements at each level in the blackboard are hypotheses about some aspect of that level. The internal structure of an hypothesis consists of a fixed set of attributes; this set is the same for hypotheses at all levels of representation in the blackboard. These attributes are selected to serve as mechanisms for implementing the data-directed hypothesize-and-test paradigm and for efficient goal-directed scheduling of KS's. Knowledge sources may create networKs of structural relationships among hypotheses. These relationships, which are explicit in the blacKboard, serve to represent Tiferences and deductions made by the KS's about the hypotheses; they also allow competing and overlapping partial solutions to be handled in an integrated manner. The Hearsayll speech-understanding system is an implementation of this organization; it is used here as an example for descriptive purposes. * This research was supported in part by the Defense Advanced Research Proiects Agency under contract no. F44520-73-C-0074md monitored by the Air Force Ofice'of Scientific Research.