Knowledge-based systems are data bases with more powerful front ends for dealing with the meaning of data. This paper discusses requirements for a conceptual schema that is general enough to support knowledge bases as well as ordinary data bases. It presents seven features that such a schema must support and evaluates various approaches to data base semantics in terms of them. The AI notations for semantic networks or conceptual graphs are highly general ones that can support all seven features. © 1981, ACM. All rights reserved.