IDEF1X 97 consists of two conceptual modeling languages. The key-style language supports data/information modeling and is downward compatible with the US government’s 1993 standard, FIPS PUB 184. The identity-style language is based on the object model with declarative rules and constraints. IDEF1X 97 identity style includes constructs for the distinct but related components of object abstraction: interface, requests, and realization; utilizes graphics to state the interface; and defines a declarative, directly executable Rule and Constraint Language for requests and realizations. IDEF1X 97 conceptual modeling supports implementation by relational databases, extended relational databases, object databases, and object programming languages. IDEF1X 97 is formally defined in terms of first order logic. A procedure is given whereby any valid IDEF1X 97 model can be transformed into an equivalent theory in first order logic. That procedure is then applied to a meta model of IDEF1X 97 to define the valid set of IDEF1X 97 models.