Using STEP in exchange of digital product information.

Transcription

1 Using STEP in exchange of digital product information. Authors Department of Electro-Technology Faculty of Electrical Engineering Czech Technical University in Prague Technická 2, PRAHA 6, Dejvice Czech Republic Phone (2) , Fax (2) WWW:{ Abstract STEP, the Standard for the Exchange of Product Model Data, is a comprehensive ISO standard (ISO 10303) that describes how to represent and exchange digital product information. The goal of this article is an introduction to the STEP standard. We also show how can be used for description of technological data in production process. 1. INTRODUCTION The STEP is the ISO standard (ISO 10303) for exchange of production data. The STEP describe how to present and exchange product information. The STEP is used in product s entire life cycle, from analysis to design, manufacturing, quality control and testing. The STEP standard is supporting geometry, topology, relationship, attributes, assemblies and configuration of product management data. The STEP standard is structured to many parts. The basic parts are complete and published, whiles more are under development. One of the most important features is STEP extensibility. The STEP standard is based on language that can describe structure of any engineering product that needs to be exchanged. This language is called EXPRESS. The definitions, which describe products in some area in industry, are called Application Protocols (AP). The Figure 1 shows the structure of the STEP standard. Application protocols are available for mechanical and electrical applications, and are under construction for composite materials, sheet metal dies, automotive design and manufacturing, shipbuilding, the AEC industry, process plants, and others. Over time, many industries will develop their own AP s. Some key reasons why STEP is important: STEP is a standard that can grow. It is based on a language (EXPRESS) and can be extended to any industry. A standard that grows will not be outdated as soon as it is published. Figure 1: Structure of STEP standard

2 The overall structure of the standard is summarized here. In words, the basic breakdown is: Parts 11 to 19 specify the Description methods, Parts 21 to 29 specify the Implementation methods, Parts 31 to 39 specify the Conformance testing methodology and framework, Parts 41 to 99 specify the Integrated generic resources, Parts 101 to 199 specify the Integrated application resources, Parts 201 to 299 specify the Application protocols, Parts 301 to 399 specify the Abstract test suites, and Parts 501 to 599 specify the Application interpreted constructs Application Protocols The STEP Parts known as Application Protocols (AP s, part series 2xx) define formal models in a designated application area. The scope of an AP is defined by: the type of manufactured product, the supported stages in the life cycle of the product, the required types of product data, the usage of the product data the disciplines that create and use the product data. Examples of some AP, which are most interested in the field of packaging, are: AP203: Configuration controlled design AP210: Electronic assembly, interconnect and packaging design AP212: (Electrotechnical design and installation) Description Methods The group of description methods (part numbers 1-12) create the base of the STEP standard. The most important method is the EXPRESS language (ISO ). EXPRESS is object oriented human readable modelling language with graphical representation. Implementation Methods STEP implementation methods (part series 2x) describe the mapping from STEP formal specifications to a representation used to implement STEP. In other words, implementation methods specify means to store, access, modify and transmit EXPRESS defined data. At present time exist following ISO parts: 2. EXPRESS The standard object oriented EXPRESS language is written to be a human readable and computer interpretable language like other computer languages for example Pascal, C++, Java, etc. The standard define the base language structures and definitions. The overall structure of EXPRESS language is similar to special object oriented languages or languages for specifying structure of object oriented databases. The data model, which is described by EXPRESS language, is similar to Entity-relationship model (ERM) or some object oriented models like Object Modelling Technique (OMT). EXPRESS is designed to be implementation independent and thus support the four levels. It defines a common interpretation of the standard in terms of data and rules. This common interpretation can be used to drive computer processes. 21 (STEP file format) 22 (Abstract STEP Data Access Interface SDAI) 27 (Java language-based SDAI) 28 (STEP data in XML) products are under development. EXPRESS has a number of dialects, which are: EXPRESS-C EXPRESS with static and behavioural modelling capabilities EXPRESS-G Graphical language EXPRESS-I Instantiation language

3 EXPRESS-M Mapping definition language SCHEMA example; TYPE date = ARRAY [1:3] OF INTEGER; EXPRESS-P Process definition language END_TYPE; EXPRESS-V Extension of EXPRESS which enables the creation of views EXPRESS-X Merger of M and V The EXPRESS language allows you to define a data model in terms of constraints, rules, and data structures. In this section, we show some of the basics of defining data structures in EXPRESS. FUNCTION years(d : date) : INTEGER; (* computes an age to the current date from d *) END_FUNCTION; TYPE hair_type = ENUMERATION OF (brown, black, blonde, redhead, gray, white, bald); END_TYPE; Entities An entity is analogous to an object with a structure data type in C++. Each entity has a name and a set of attributes. Each attribute has a name and a data type. An entity definition has the following form: ENTITY Entity name; a1: data_type; a2: data_type; ENTITY female;... an: data_type; For example a point entity might be defined as follows: ENTITY Point; x: REAL; y: REAL; END_SCHEMA; ENTITY person; SUPERTYPE OF (ONEOF(male, female)); first_name : STRING; last_name : STRING; nickname : OPTIONAL STRING; birth_date : date; children : SET [0 :?] OF person; DERIVE age : INTEGER := years(birth_date); INVERSE parents : SET [0 : 2] OF person FOR children; SUBTYPE OF (person); husband : OPTIONAL male; maiden_name : OPTIONAL STRING; WHERE WI : (exists(maiden_name) AND EXISTS(husband)) OR NOT EXISTS(maiden_name); ENTITY male; SUBTYPE OF (person); wife : OPTIONAL female; The data type of an attribute can be a simple type, an aggregate type, a defined type, an enumeration type, an entity type, or a select type. The EXPRESS language supports several types of inheritance relationships. The following example shows one type of inheritance relationship supported by EXPRESS: ENTITY Point3D SUBTYPE OF (Point); z : REAL; The entity Point3D will have three attributes: x and y that are "inherited" from Point and z, which is declared locally. At this moment is a possible show a more complex example of the EXPRESS language usage. 3. TOOLS At present time exist many producers of EXPRESS/STEP tools. I will concentrate on some of them. Some of them are free, but the most important are commercial. University of the Federal Armed Forces Tool Name WinSTEP (Version 3.0) STEP Toolkit for Windows Free

4 WinSTEP is a STEP Toolkit for Windows. Version 3.0 was released in March 1998 although version 2.0a is still available. Version 3.0 is based on an improved STEP class library (received from NIST). WinSTEP is a collection of useful tools dealing with STEP (EXPRESS) running on top of Windows. This version is based on fedex V beta (June 1995). Most improvements are based on the incorporated C++ translator. LKSoftWare GmbH Tool Name J-SDAI SDAI implementation in Java Free version for AP203 The JSDAI Core API is a fully conformant implementation of ISO "Java programming language inding to the standard data access interface with Internet/Intranet extensions." The JSDAI Core API is used to manage populations of STEP data. It simultaneously supports both late and early binding to access entities and attributes. National Institute for Standards and Technology Toolkits Free NIST Expresso is a language environment for EXPRESS providing tools to aid in the development and validation of EXPRESS information models and representative Part 21 data sets. The program translates EXPRESS schema into an object-oriented internal representation, creating class definitions and methods for EXPRESS types, functions and rules. Data corresponding to the EXPRESS may be loaded from part 21 files or created through the user interface. NIST Expresso allows one to validate the loaded data against constraints (WHERE rules, global rules etc.) specified in the EXPRESS schema, provides entity type hierarchy graphs, allows incremental definition of EXPRESS code and an interface for creation and viewing of instance data. STEP Tools Inc Toolkit Commercial STEP Tools Inc. has tools and services for software development, CAD geometry, translation, internet publishing, and training that can help you develop and deploy STEP applications and databases throughout your organization. STEP Toolkit for STEP developer and EzExpress Editor Funkcionality Libraries and editor Avaibility Free STEP Toolkit contains programming libraries and tools that can be used to build software that works with STEP data and EXPRESS schema. This version is based on SCL from NIST. EzExpress editor is an Express language editor which has IDE(Integrated development environment). Embeded Express compiler can be used to generate SCL C++, CORBA-IDL, and ObjectStore C++ codes. 4. XML AND STEP XML (Extensible Markup Language) is a textual language for "structured data format" that are easy to generate and read. XML became an ISO standard in February XML inherited from SGML (Standard Generalized Markup Language, ISO 8879), which was developed in the early 1980s and approved in 1986 as an ISO standard. XML is also related to HTML (Hypertext Markup Language), which is used for the creation of Web pages. XML standard is attractive choice for binding EXPRESS schemas and data due to many reasons. Therefore was established SC4 Project Number : Implementation methods: XML representation of EXPRESS schemas and data. Implementation of EXPRESS schemas and data by XML has many advantages:

5 XML parsers are inexpensive and easy to obtain. Internet browsers will be soon able to parse XML and will include standardized application programmer interfaces for manipulating XML data. which are provided by our Department of Electrotechnology at Electrical Engineering Faculty of Czech Technical University in Prague and try established the first research goal in the area of using the STEP/EXPRESS standard in the area of the packaging. XML is well suited both for data exchange over the Web and for producing human readable output in numerous formats. Thus, XML satisfies the dual nature of modules. For example, consider the following EXPRESS definition of a point on a plane with x and y axes: ENTITY point; x : REAL; y : REAL; This EXPRESS definition specifies a point with the two attributes whose values are real numbers corresponding to the point s x and y coordinates. An early-bound XML serialization of a point might look something like this: <point id= e1 > <point.x id= a1 > <real /></point.x> <point.y id= a2 > <real /></point.y> </point> 5. CONCLUSION The aim of this article was a brief explanation of STEP standard and EXPRESS language. The STEP standard is the most important development in the area of an exchange of production data between different producers. The STEP standard is supported by U.S.A. government and many of the most major worldwide producers e.g. General Electric, etc. Our educational and research project in the area of using the STEP/EXPRESS standard is put basic information about this standard in the courses 6. REFERENCES [1] STEP Tools, Inc.: Introduction to STEP, [2] LKSoftWare GmbH: LKSoft, a solution provider for STEP (ISO 10303) and JavaTM technology, 2002 [3] Peter R. Wilson.: EXPRESS Tools and Services(1998), [4] Joshua Lubell: An XML Repository Architecture for STEP Modules, National Institute of Standards and technology [5] David Loffredo: Fundamentals of STEP Implementation, STEP Tools, Inc. [6] Martin Hardwick: STEP Data Exchange Standard Moves Into Implementation Phase, STEP Tools, Inc. [7] Martin Hardwick: The STEP Standard, [8] STEP Tools, Inc.: ROSE Library Tutorials, 8 Getting Started with EXPRESS, utorial/roselib_tutorial_8.html [9] Robin Cover: STEP/EXPRESS and XML, [10] Martin Hardwick: STEP Database Tutorial, STEP Tools, Inc. [11] Chuck Eastman: Introduction to EXPRESS, CIS/2 Notes, Georgia Tech [12] Stefan Schwarz: Java as a labguage for STEP-based product and process modeling, University of the Federal Armed Forces Munich [13] EXPRESS ENGINE PROJECT, [14] The NIST STEP Class Library,

6 Figure 2: ExExpress - editor of the STEP/EXPRESS standard Figure 3: JSDAI STEP-Book AP210, interconnect design