Product Data Exchange Using STEP
Today more and more computer-aided application software(CAX) systems are used
in various tasks at certain stages of product design and manufacturing in order
to improve productivity. Since these systems are mostly developed separately
with data generated and stored in a format without consideration of others,
there is an urgent need to exchange product data between systems within
corporations or even between partners across corporation limits. Furthermore,
total optimization and shorter development time with lower costs can be
achieved if these systems can be integrated together.
To facilitate data exchange between different systems a lot of product data
exchange standards have been made, such as IGES, CAD-I, PDDI, SET. They are
widely used and show efficiency of data exchange using standards. In the
meantime, these standards also expose many problems in the application. Among
these problems loss of information is the most fatal one which is caused by the
incompleteness of product information defined in these standards.
The emerging international product data exchange standard--STEP (Standard for
The Exchange of Product model data) was developed based on the experience of
other product data exchange standards and aimed at overcoming their shortages.
The objective of STEP is to give a complete, unambiguous,
computer-interpretable representation of product data throughout the life cycle
(design, engineering analysis, manufacture, support and maintenance and
disposal) of a product. The completeness of this representation makes it
suitable not only for neutral file exchange, but also as a basis for
implementing, sharing and archiving product databases.
STEP also presents a new methodology. The fundamental of STEP methodology is
its 3-layer schema in accordance with 3-layer structure of database:
application layer, logical layer and physical layer. Therefore, in defining
semantic models, we can use functional analysis to derive need specifications,
and then use need specifications to derive implementation specifications. This
makes STEP independent of application and any specific computer system .
In our project we tried to implement a product data exchange interface based on
STEP. The interface is composed of the following parts:
- Conceptual Model: According to analysis of application needs of our system a
subset of STEP data model is selected as the conceptual model. Described in
EXPRESS, this conceptual model can be generated using application protocol.
However, as application protocols are still in development in STEP, in our
initial practice this conceptual model was generated according to our
analysis.
- Access Software: Access software is a unified data access interface similar
to SDAI in STEP. Application software and the translator access data through
this interface. Therefor, whatever fundamental data storage and management
system the CAX system uses, application software and the translator always
access data via the same function calls, i.e. they are independent of data
access mechanisms;
- Translator: The translator translates data from STEP data model into CAX data
model or vise versa. According to its function the translator can be divided
into 2 parts: one, called preprocessor, translates data from a specific CAX
system format into STEP standard format; the other, called postprocessor,
translates data from STEP standard format into a specific CAX system format.
Due to the development of access software, we only need to consider conceptual
mapping in this part.
A prototype of an interface for our CAD system was developed.
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