The manner in which CARMEN (Constraints And Rules Management ENgine),
an operational expert system generator developed as part of the ESPRIT
project ITHACA, models and acquires knowledge is discussed. Central t
o CARMEN are three types of control entities (TASKs, MKSs and BKSs) wh
ich are used to describe problem-solving at the knowledge-use level. M
odeling of domain knowledge is done both at the deep and surface level
s. The Integrity Checking Task (or ICT) is used to illustrate the mann
er in which CARMEN works. We conclude the paper with a comparison of C
ARMEN with other approaches in knowledge modeling.