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The NIST EXPRESS Toolkit is a software library for building EXPRESS-related tools. This paper gives an introduction, overview, and history of the toolkit. This paper also describes how to get more information on the toolkit. No knowledge of EXPRESS or the EXPRESS Toolkit is presumed

This paper describes a set of minor modifications to yacc-like tools that allows them to be used in a straightforward way to parse ambiguities and, more generally, grammars that require an indefinite amount of lookahead. Required changes to the lexical analyzer are also discussed, and the application of these techniques is illustrated within the context of specific examples

The NIST EXPRESS toolkit is a software library for building EXPRESS-related tools. The toolkit was previously released in 1991, based on ISO TC184/SC4 N14 (familiarly called "EXPRESS N14"). The current release is based on Draft International Standard (DIS) 10303-11 (N151) and while the philosophical underpinnings are similar, much of the interface has changed significantly. This paper describes changes that must be made to existing applications so that they can work with the new toolkit. This paper should be read by anyone maintaining software based upon the NIST EXPRESS toolkit. This paper will also provide insight to people interested in the internals of EXPRESS implementations and some of the ways they have changed over time due to experience and the different EXPRESS specifications. Keywords: compiler, EXPRESS; implementation; National PDES Testbed; PDES; STEP Context The PDES (Product Data Exchange using STEP) activity is the United States' effort in support of the Standard for ...

The NIST EXPRESS toolkit is a software library for building EXPRESS-related tools. The EXPRESS Toolkit is based on Draft International Standard (DIS) 10303-11 (N151). The NIST Part 21 Exchange File Toolkit is a software library for building Part 21-related tools. The Part 21 Toolkit is based on DIS 10303-21. This paper describes how to obtain the toolkits and install them. No knowledge of EXPRESS or the EXPRESS Toolkit is presumed other than a familiarity with file transfer and similar installation procedures. A rudimentary grasp of the theory of typical computer language implementations is useful but not necessary. Keywords: compiler, EXPRESS; implementation; National PDES Testbed; PDES; STEP Context The PDES (Product Data Exchange using STEP) activity is the United States' effort in support of the Standard for the Exchange of Product Model Data (STEP), an emerging international standard for the interchange of product data between various vendors' CAD/CAM systems and other manufact...

1 Motivation Writing a language processor from scratch is a daunting task. The current interest in generative approaches, where (parts of) language processors are generated automatically from formal specifications of the language, comes as no surprise. Early examples are parser generators like Yacc [8], which generate parsers from

Process of breaking input into tokens. Sometimes called “scanning ” or

Syntax : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 14 2.4 Simple types : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 18 2.5 Structured types : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 23 2.6 Values : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 30 2.7 Transfer Syntax : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 32 2.8 Macros (not available yet) : : : : : : : : : : : : : : : : : : : : : : : : 35 3 Theory of operation 37 3.1 Cohesive set of tools : : : : : : : : : : : : : : : : : : : : : : : : : : : 37 3.2 Model of types : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 38 3.3 Model of values : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 40 3.4 Free value activation : : : : : : : : : : : : : : : : : : : : : : : : : : : 42 4 Advanced usage 46 4.1 Building freeval : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 46 4.2 Reconfiguring activations : : : : : : : : ...

In 1990, NIST released a software toolkit for building EXPRESS-related tools. The software was based on early drafts of EXPRESS and included a parser, a resolver, and a framework for producing schema -independent tools. During the past year, we have redesigned the toolkit with respect to user experience and the EXPRESS Draft International Standard. Our work will be of interest to implementors of EXPRESS tools and toolkits. This paper describes our work and the current state of the NIST EXPRESS toolkit. As well as describing our efforts in improving the toolkit performance, we will comment on: . the "hard" parts of implementing the EXPRESS language, . things we did wrong, . several implementation-dependent extensions to EXPRESS, . sophisticated error and warning detection. We will also revisit our original ideas underlying the toolkit concept. We will discuss whether, in light of our experiences, the concepts still make sense, can be amended, or should be entirely scra...

The NIST EXPRESS Toolkit is a software library for building EXPRESS-related tools. This paper gives an introduction, overview, and history of the toolkit. This paper also describes how to get more information on the toolkit. No knowledge of EXPRESS or the EXPRESS Toolkit is presumed other than a rudimentary grasp of basic computer science. Keywords: compiler, EXPRESS; history; implementation; National PDES Testbed; PDES; STEP Context The PDES (Product Data Exchange using STEP) activity is the United States' effort in support of the Standard for the Exchange of Product Model Data (STEP), an emerging international standard for the interchange of product data between various vendors' CAD/CAM systems and other manufacturing -related software [10]. A National PDES Testbed has been established at the National Institute of Standards and Technology to provide testing and validation facilities for the emerging standard. The Testbed is funded by the Computer-aided Acquisition and Logistic Sup...