A framework for managing access to data that involves three layers or schemas: the external or programming view, the conceptual or data administration view, and the internal or database administration view. Such ideas were developed by an American National Standards Institute/Scalable Processor Architecture subcommittee in 1971 but received little practical implementation by database management system (DBMS) vendors. The principle is that the conceptual schema consists of business rules derived from a semantic data model, which provides independence between programs and data structures. The emphasis has since shifted to computer-aided software engineering (CASE) tools and “repository” standards.