STEP[ISO1], the Standard for the Exchange of Product model data, specifies a description of product data throughout its life cycle in a computing platform-independent manner. An Application Protocol (AP) in STEP defines the information requirements for a particular area of design, manufacturing, engineering, or product support. APs provide a neutral representation for sharing product data among dissimilar software applications. Each STEP Integrated Resource (IR) defines a set of re-usable constructs that serve as building blocks for developing APs. These constructs are specified using an information modeling language called EXPRESS[ISO11]. APs are developed according to a rigorous methodology[PALMER] dictated by the STEP community. The end result of this development process is a standards document that specifies the AP's requirements and a technical solution for data exchange that uses STEP technology.
The STEP community is international in scope and includes participants from numerous industries and research institutions. Over twenty-five nations and more than 200 companies are currently involved in developing STEP. A typical STEP AP team has four or more people, typically not all working for the same company or even living in the same country. It takes this team, on the average, a year and a half to produce an initial AP specification for a typical engineering function. Thus AP development is both time-consuming and expensive.
There are two principal reasons why AP development is so cumbersome. One reason is the geographical and organizational dispersion in the STEP community. The other is the lack of an integrated STEP-tailored software environment for AP developers. To address these issues, NIST is building an Internet-accessible, integrated software tool suite in order to accelerate the AP development process and to improve AP quality. This software environment uses a central information registry, the AP Information Base (APIB)[LUB96].
The APIB is an on-line repository under development at NIST for users
and developers of STEP. The APIB currently contains only STEP IRs.
When it is complete, the APIB will also contain APs, other STEP
documents describing representation and implementation methods, and
additional information useful to the STEP community such as schedules,
issue logs, and issue resolutions. The APIB's contents are indexed
for efficient access using a text retrieval engine[OTC]. Each document in the APIB is stored in its native
format. Translation for viewing or publishing purposes is
done on demand. APs and IRs are represented in the Standard
Generalized Markup Language (SGML)[GOLD], a language for describing the structure of documents
for use in text processing applications
. AP and IR documents are marked up using SGML
document type definitions (DTDs) that have been developed specifically
for the requirements of STEP[PHIL]. Other
documents will be represented as plain ASCII text, or in SGML using
DTDs less complex than those for APs and IRs. The text retrieval
engine uses the SGML markup in the APs and IRs to index their data.
Thus users can issue queries to the APIB referring to the SGML
structures specified for STEP.
This paper describes a World Wide Web interface to the APIB. This
implementation makes use of the Common Gateway Interface (CGI)
standard for interfacing external applications with web servers[BLEE95]. CGI scripts generate HTML dynamically in
response to requests for web pages. The APIB gateway uses HTML forms
to obtain input data from the user. The input is then processed by
the APIB gateway's CGI scripts. The APIB gateway provides APIB access services to
STEP AP developers through their web browser software, eliminating the
need for AP developers to install APIB client software. It also
eliminates the need for NIST to build and maintain separate APIB user
interfaces for multiple computer platforms.