A Conceptual Data Model of Datum Systems

Traditionally, geometric dimensioning and tolerancing (GD&T) requirements have been exchanged with technical drawings. However, with the advent of computer-aided design, manufacturing, and inspection equipment, the ability to exchange these requirements in a computer-sensible manner has become increasingly more desirable. As “a data model is an effective technique to define the shareable semantics that are essential to the success of data communication in an integrated environment” [1], a conceptual data model has been developed that defines a portion of the semantics necessary for the electronic exchange of GD&T data among the design, manufacturing, and inspection divisions of an enterprise. The portion of the semantics that this data model defines encompasses the concepts of datum systems, datums, datum features, and datum targets. This paper presents this data model, which will be referred to throughout the remainder of the paper as the DSCDM (Datum System Conceptual Data Model). Additionally, a portion of the data model presented in STEP Part 47 [2] is reviewed and a comparison is made between it and the DSCDM. The model presented in STEP Part 47 will be referred to as “the Part 47 model” throughout the remainder of this paper.