KNOWLEDGE ACQUISITION IN RULE-BASED SYSTEMS—KNOWLEDGE ABOUT REPRESENTATIONS AS A BASIS FOR SYSTEM CONSTRUCTION AND MAINTENANCE11This work was supported in part by the Bureau of Health Sciences Research and Evaluation of HEW under Grant HS-01544 and by the Advanced Research Projects Agency under ARPA Order 2494. It was carried out on the SUMEX Computer System, supported by the NIH under Grant RR-00785.