66. A computer having a memory storing a predefined knowledge base including control knowledge, factual knowledge, and judgmental rules for encoding knowledge about a particular problem domain, said factual knowledge including definitions of classes of objects, attributes defining characteristics of said objects, and structures of said classes and attributes, said computer operating under control of a stored program interpreting the knowledge base to conduct a consultation with a user regarding a specified problem in said problem domain, said stored program including means for creating instances of said classes representing particular objects, a question and answer facility for recognizing questions from the user and formatting responsive answers including an explanation of the basis for the answers, and means for determining values for said attributes and said instances of said classes describing said characteristics of said particular objects, an inference engine for applying said judgmental rules to determine the responsive answers to said questions and for resolving conflicting conclusions of said judgmental rules, wherein the improvement comprises: said knowledge base has a separate portion encoding said control knowledge separate from said factual knowledge and said judgmental rules, said control knowledge being encoded in an imperative procedural language defining a sequence of steps for conducting said consultation with the user, and further comprising language interpreter means for executing said imperative procedural language, said separate portion of said knowledge base encoding said control knowledge comprises a plurality of discrete control blocks, each control block including statements in said imperative procedural language, said statements including separate statements to ask the user a question and obtain a responsive answer, apply a specific set of said judgmental rules, display to the user the conclusions of the rules applied, and to execute another specified control block, said plurality of control blocks including at least one post-instantiation control block associated with at least one of said classes, at least one determination control block defining a predetermined method for determining a value for at least one of said attributes being undetermined and being included in the premise of one of said judgmental rules, and at least one post-determination control block using a determined value for a determined attribute, and wherein said procedural language interpreter comprises means for interrupting the execution of said procedural language to execute the procedural language statements in the post-instantiation control block when an instance of the associated class is created, means for interrupting execution of said procedural language to execute the procedural language statements in the determination control block when said inference engine applies said judgmental rule including said undetermined attribute, and said language interpreter means includes means for interrupting the execution of said procedural language to execute the procedural language statements in the post-determination control block when said judgmental rule determines the value for said undetermined attribute.
69. The computer as claimed in claim 66, wherein said factual knowledge base includes means for defining at least one of said attributes as multivalued, means for defining hierarchies of legal values for said multivalued attribute, and wherein said inference engine comprises means for determining certainty factors for concluded legal values of said attribute, and said knowledge base interpreter includes means for propagating the determined certainty factors through said hierarchy of legal values.