Wagner presents the abstract syntax and semantics of a new object-oriented programming language called Language for Data Directed Design (LD³). He is interested primarily in theoretical issues, considering language implementation the last step in language development.

LD³ has no built-in data types; a new type is defined by specifying operations applicable to the objects of this type. Formal definitions of syntax and denotational semantics are presented, followed by three examples of data type specification: Boolean type, integer, and stack. The current emphasis is on information hiding and language extensibility, and the project of full definition of LD³ is not yet completed; the author mentions the need for future investigation of such concepts as inheritance, overloading, and generic types.