The design and implementation of the Ada [1] programming language was commissioned by DoD with the intention of requiring most future military systems to be programmed in Ada. It is therefore necessary that Ada be precisely understood by both its users and implementers, in order to ensure the quality of systems written in Ada. In particular, since DoD must control Ada compiler implementations, a precise, well-structured, and validated formal definition of Ada can provide one of the principal standards to which these implementations must adhere. Beyond such considerations pertaining to particular programming languages such as Ada, good generic research toward the design and implementation of tools and methodologies for supporting the development of precise, readable, and accurate formal definitions has considerable relevance to the broader goals of understanding large programs and verifying their correctness.