F I N A L Y E A R P R O J E C T R E P O R T
Project title: Develop an
open business information system
using the emerging international
data exchange standard ‘STEP’
This report has been submitted for assessment towards a Bachelor of Engineering degree in the School of Electrical, Electronic and Information Engineering, South Bank University.
This report is written in the author’s own words and all sources have been properly cited.
1Abstract
This project is based on an emerging international standard defined by the International Organisation for Standardisation in ISO 10303. The standard is abbreviated as ‘STEP’ which is standing for ‘STandard for the Exchange of Product model data’ and is concerned with product data exchange between computer systems with different applications.
Its important trait is not to consider the syntax of data being transferred and to provide a platform for interfacing with applications, that do not have the same internal data structures.
The project is an application of this standard in the electronic industry domain. It shows how product data models in STEP are defined and implemented. Furthermore the underlying architecture of this standard and the product data transfer are covered.
The report finally takes into account test results obtained and difficulties, that should be solved to improve the standard and increase its acceptance.
2Acknowledgements
I am indebted to my supervisor Dr. F. Cheng who provided helpful and constructive criticism throughout my project work.
Special thanks to South Bank University and Hochschule Bremen for offering the opportunity to study in London.
Table of contents:
1 Abstract______1
2 Acknowledgements______1
3 Introduction______3
4 Aims and objectives______5
5 Deliverables______6
6 Technical background and context______6
7 Technical approach______9
7.1 The idea behind STEP______9
7.2 The STEP conforming data transfer______10
7.3 The product model______13
7.3.1 Modelling the product model______13
7.3.1.1 The Nijssen Information Analysis Method______14
7.3.1.2 The schema 'EL_PARTS'______20
7.3.2 The data definition language EXPRESS______25
7.4 The implementation in STEP______29
7.4.1 The STEP architecture______29
7.4.2 The Standard Data Access Interface______31
7.4.3 Relational database management systems versus object oriented database management systems (OODBMS) 35
7.4.4 Establishing the conceptual schema in database management software____35
7.4.4.1 The implementation of the schema 'ELEC_DEVICE' applying the database management system ACCESS 36
7.4.4.2 The DBase IV database and the conceptual product model schema____40
7.4.5 The data transfer between DBase IV and ACCESS in STEP data format__41
8 Results and discussion______43
9 Conclusions and recommendations for further work______46
10 Bibliography and References______47
10.1 Bibliography______47
10.2 References______48
11 Project Planning______49
11.1 Main tasks and time estimated______49
11.2 Milestones______50
Appendix 1a - 1c Project network plan, Gantt chart and alterations
Appendix 2Abbreviations and acronyms 1
List of figures and tables 3
3Introduction
This project addresses the problem of exchanging product model data between computer systems in a standardized form. It seems not to be a new area of work but hitherto especially in the CAD domain standards for data transfer have only focused on the exchange of geometrical or draughting data. A major problem has always been that both the sending and the receiving system had different applications and hence not the same internal data structure. This fact is now compensated for through the emerging standard STEP, that has been created to support these data transfers and is defined by the International Organisation for Standardisation in ISO 10303, the standard for Industrial automation systems and integration - Product data representation and exchange. This standard is usually referred to as ‘STEP’, which stands for ‘STandard for the Exchange of Product model data’. It uses an intermediate neutral data transfer format which reduces the number of conversion programs necessary for each computer system to two.
The platform for the description of products in STEP is the ‘product model’, that is a data structure for the representation of product definition data. "The general idea of a product data model is a conceptual description of a product, capable of structuring all the information necessary for the design, manufacture and use of that product. Rather than as a single database, it is viewed as a common language for the description of a particular type of product or as a more complex and complete form of a traditional classification system" (Björk, Wix 1991).
In my project I used as an example a company which produces a large number of different kinds of electronic components and has customers throughout the whole world. It should be possible for a purchaser to use the manufacturer’s product data in the form given on his computer system via data exchange in STEP data format and vice versa.
Therefore my general aim in this project was to create a product data model and to use it as an ‘Open Business Information System’ between computers with different internal data structures. This is meant that the data model not only had to be implemented in several programs but also data transfers in standardized form had to be made to verify the work.
Further information about realisation is given in the following paragraphs which start up with a detailed description of the aims and objectives of my work followed by a list of deliverables. Then I explain the technical background and context of the project work. The next section is about the technical approach and shows in detail the realisation of my aims, which are then discussed against the results. In the last paragraph I present my conclusions and recommendations for further work together with a list of references and bibliography. Finally an extra section gives a survey about the way I planned my project work. The report is completed by an attached floppy disk and several appendices which are referred to throughout the text.
4Aims and objectives
My general aim was to develop a product data model by adopting the STEP methodology and to use it as an Open Business Information System. This required an understanding of what this standard is about and the need to describe products, to implement their semantic definition on computers and to transfer these definitions as well as sample data in STEP data format. This led to the following main tasks:
First I searched for information and did background reading, to improve my understanding of STEP. This was done by using the Perry Library as well as the CD-ROM information system in the Learning Resources Centre and the World-Wide-Web.
In addition I read the information given by my supervisor. Without doing this it would not have been possible to realise the project. Hence it was one of the milestones I defined. More about milestones are shown in the paragraph that covers project planning.
The next task was the conceptual description of the product data model. Developing this model needed first my creativity and my knowledge about the characteristics of electronic components. The quality of all further work was dependent on making a comprehensive description of the product data model. Therefore this was a crucial part in my project. The realisation of the model was done using given software. I will describe this in detail in the section about the technical approach.
The development of the ‘Open Business Information System’ made it necessary to implement the concept of the product data model into a database. To be able to do this I had to learn the database management system ACCESS.
Another task was to use the database management system DBase IV. This means that I had to make an implementation of tables in this database system for querying the ACCESS database to get information out of it.
The next aim was to produce the files, that are essential for transferring
data in STEP data format. The bases for this work have been the
ACCESS database and the tables created using DBase IV.
The following but also important part was to test the system and verify
that all components work together as specified. Details about the specification are part of the system’s development and will be shown in the section about the technical approach. In this phase I had to specify test conditions and to check if the ‘Open Business Information System’ meets its specification.
5Deliverables
The key deliverables of the project as the main outputs of my work are
closely related to the aims and objectives described above. They are therefore as follows:
A conceptual description of the product data model,
a database written in ACCESS, that reflects the product data model,
tables created by using the database management system DBase IV,
files needed to make data transfers in STEP data format and
the final year project report
6Technical background and context
Before the idea of STEP was born several standards were developed since 1979, which were all concerned with the exchange of draughting and geometric data only. Throughout the 1980’s it became apparent that graphic data exchange would not be sufficient for future engineering systems. Although there was no clear definition of what such future systems would have to be able to do, it was recognised that data exchange has to be considered as a primary feature and not as a secondary aspect. Hence data exchange must influence the design of computer systems to ensure that they are able to communicate with each other. Therefore STEP is intended as a world wide standard. The development of STEP started in the mid 1980's and those parts of it which are available and standardized are the result of a big international effort. Examples of countries that are involved are Australia, Belgium, Canada, Denmark, France, Finland, Germany, Hungary, Japan, Netherlands, Norway, Sweden, Switzerland, United Kingdom, and United States of America (Björk, Wix 1991).
However, there has been a considerable amount of activity in this area for more than one decade, and STEP is still being developed. The work that has been done includes fundamental research as well as applications. A few examples are:
STEP conforming integrated facility management (F. Cheng et al. 1995). This project deals with supporting an integrated information system in the estate domain and addresses the problem of data exchange between separate information systems by integrating already existing sources.
STEP-based information systems in integrated environments - A case study (S. Schwarz 1995). Schwarz shows how STEP can be used to develop a graphical information system for the building industry and covers all important aspects of the standard.
The MARITIME AP Factory: A modelling environment for application protocols (W. de Bruijn et al. 1995). This is more a research project than an application of STEP because it covers the problems related to the definition of application protocols (AP) in STEP.
ATLAS integration tools (P. Poyet 1995). This paper about the European Union project ATLAS explains the attempts which have been made so far to develop software tools according to STEP and addresses especially the 'Standard Data Access Interface' (SDAI) which is defined in part 22 of ISO 10303.
CIMSTEEL integration standards (A. Watson, A. Crowley 1995). The authors give a survey about the applicability of STEP to the exchange of engineering data in the steel frame industry.
Data exchange of 3D building models based on STEP (W.R. Haas 1995). Haas introduces part 225 of ISO 10303, a quite new way for transferring 3D models in the building industry, that is currently under development.
CONCEPTUAL modelling approaches in the COMBINE project (A.M. Dubois et al. 1995). The paper is about the European project COMBINE and deals with the development of heterogeneous design tools for the building industry, adopting the STEP methodology.
As already mentioned, the above listed papers are only examples of STEP related work. Indeed the world wide web includes more than two million pages about ISO 10303. That indicates the enormous number of activities in this area and also the problem of finding specific or relevant information in the internet unless the page number is known. Although much more work has been done than I can refer to in this report, I could not find anywhere papers about projects that are comparable with my work. Hence I am sure that the 'Open Business Information System' will make a contribution to the application of STEP that can be further used. Moreover it will help others to understand the general context and principles of this emerging and important standard.
7Technical approach
It is clearly beyond the scope of my project and hence of this report to give the full explanation about all capabilities STEP has and is intended to have in future. Therefore I will focus on my work and include a wider context where appropriate.
Nevertheless it is important to consider some essential characteristics which are building the frame STEP are working in.
7.1The idea behind STEP
As already mentioned above standardisation efforts in recent decades have focused only on exchanging draughting and geometrical data. Although there was no clear definition of what future computer systems would have been able to do, it was recognised in the early 1980's that such systems would have to comprise a range of capabilities that exceeds transferring draughting data, to improve competitiveness of several sectors in industry. This is especially true for the engineering domain where data exchange between computer systems is a fundamental aspect even though it covers only one area of complex engineering work.
Besides data exchange the most important sector nowadays is probably product modelling and its archiving throughout its life cycle. This is because an increasing number of users of data models is not humans but computer systems which do not rely on visual depictions which humans require. For example automated production lines and robots are capable of interpreting product data directly without using symbology and visual illustration. Drawings as needed for the human cognitive process are meaningless for them.
Exactly the aforementioned problems are met by STEP that offers the 'product model' as a platform for describing products. The product model is envisaged as a data structure for the representation of product definition data independent of any particular system. Its general idea is a conceptual description of a product, which can structure all the information necessary for the design, manufacture and use of that product. Tools necessary for the definition and description of product models are provided by STEP. I will describe one of them later.
Due to these facts ISO 10303 is intended for use in several engineering domains. Examples are Computer Aided Drafting and/or Design (CAD), Computer Aided Software Engineering (CASE), Computer Aided Manufacturing (CAM), Computer Integrated Construction (CIC) and Computer Aided Maintenance Management (CAMM).
But this leads us back to the data transfer area again. The problem in data exchange has always been the different internal data structures of the computer systems that are involved. This difficulty is now compensated for by the standard for Industrial automation systems and integration - Product data representation and exchange, that is usually referred to as STEP - STandard for the Exchange of Product model data. This emerging standard uses a neutral data transfer format which can be 'understood' by the receiving system as well as the sending one.
That sounds quite straightforward but the question is how this can be achieved. We will look at this in more detail in the next section.
7.2The STEP conforming data transfer
One important aspect of STEP is that it does not determine how data must be physically stored. It is only concerned with exchanging the semantics of data. To understand this, it is useful to look at the architecture data can be embedded in. One common approach to envisage architecture is to choose the well-known level model, that is shown below in figure 1 and uses the ANSI/SPARC terminology. This model was defined first by D. C. Tsichritzis et al. (1978).
The external level is the individual user level. Its appearance can vary depending on the users' requirements. The internal level stands for the syntactic of data, which is deduced from the conceptual level. In other words, the syntactic is the interpretation of the semantics as defined at the conceptual level. Without interpretation all data would be meaningless. Hence the conceptual level can also be regarded as an interface for the mapping between the internal level and the external level.
The conceptual level I will take up again later. For the time being we are concerned with the internal level and the external level only. Nevertheless the level model should be kept in mind because I will refer to it several times throughout the report.
It is a main feature of STEP that the internal level and hence the physical storage of data is not of interest for data exchange. This is achieved by providing a pre-processor and a post-processor for every computer system involved. For the explanation of the underlying structure it is useful first to have a look at figure 2 below, which shows the principle of STEP conforming data transfer. There we can see that data which is intended to be sent (for example 'aaa') is translated from the internal level into a neutral data format ('xxx'). This means that after the conversion process there is no further interpretation of the data, that is dependent on the internal data structure of the sending system. The data are now on an external level, which is 'understandable' by the receiving system as well as the sending one. This is because, from the viewpoint of the translation program, the data has got a new syntactic. We can also say that the data is interpreted in another way which is based on the semantics of the converter as defined on its conceptual level.