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Ph.D. Theses

Efficient Database Implementation of EXPRESS Information Models

By David Loffredo
Advisor: Martin Hardwick
April 10, 1998

The research presented in this thesis describes a framework for database implementation of EXPRESS information models. EXPRESS models describe complex structures and correctness conditions for engineering activities, and are defined by the ISO-10303 Standard for Product Data Exchange (STEP). These models are a substantial engineering resource, and industry desires to use them to integrate design and manufacturing processes. Databases built around STEP models are essential because they provide content that integrated engineering processes understand.

The Standard Data Access Interface (SDAI) is a STEP API for EXPRESS-defined data. Prototypes have attempted to provide SDAI access by implementing each SDAI operation as one or more native operations directly upon the database. A direct binding can be costly, as it requires completely new software for each database. This work proposes several SDAI implementation architectures that offer alternatives to a direct binding.

To evaluate the real-world performance of implementations, this work defines a set of representative benchmarks on the STEP AP-203 information model. AP-203 contains information such as CAD geometry and product configuration that is common to all of the STEP models. The STEPStone benchmarks cover information that is modeled in an existence dependant style (PartStone, part versions), a navigational style (NURBStone, geometry), and a mix of the two (BOMStone, bill of material).

The results of timing experiments using these benchmarks are presented. The experiments evaluate the performance of direct-binding SDAI implementations built on relational and object-oriented databases, and examine the effect of various optimizations on binding performance. Analysis of the timing results provide the relative cost of access for each system, and allow us to determine when each implementation style will be most advantageous. In addition, these experiments provide insight about the use of SDAI access versus traditional access strategies.

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