Abstract: A rule-based system, concerned with a domain of knowledge or operations (the domain theory) and having associated therewith a rule-based entity relationship (ER) system (the ER theory) which represents the domain theory diagrammatically, is supported by a computer system. The system, which constructs a new rule for the domain theory, controls the entry into conditions storage memory or note pad (16) of conditions which together represent the desired rule, and rule assembly logic (17) that generates the desired rule from those entries. A display device (14) displays an ER diagram (FIG. 2) obtained from the ER theory and stored in memory (11, 12). An operator selects, via a mouse and control logic (13, 15), elements of the ER diagram. These elements are entered into the conditions storage means or note pad (16). Attributes are entered via a combination of selection from the ER diagram and semantic constraints on their values.