Reducing Parts Diversity in Product Design: a Data Centered Approach

To appear in: Proceedings of CE'2003, Special track on Data Integration in Engineering, Madeira, Portugal, 26-30/07/2003 Reducing parts diversity in product design: a data centered approach

Jérôme CHOCHON & Yamine AIT-AMEUR & Guy PIERRA & Jean-Claude POTIER Laboratory of Applied Computer Science (LISI), National Engineering School for Mechanics and Aerotechnics (ENSMA), Poitiers 86960 Futuroscope Cedex - France {chochon½pierra½yamine½[email protected]}

ABSTRACT: To attract customers, manufacturers must design a large diversity of variants of products that suit to various requirements. But to reduce cost, manufacturers must reduce the diversity of components. We focus on part diversity, i.e. when two or more parts satisfy to the same need. Parts are described in several independent documents, or database, each one with its own information model. We claim that, to a large extend, part diversity results from lack of information and information exchange within the extended enterprise. So we propose to capture the whole part information through a single computerized representation based on the PLIB data model (ISO 13584). But designers must keep their own view of parts. So, various human-readable presentations will be generated from the PLIB representation by tools. One example is given. We discuss the creation of a database of fasteners in a manufacturing industry. We present the various steps to build the PLIB data model and we outline existing and in progress tools to generate various human-readable presentations (website in DHTML, paper document, …).

1 INTRODUCTION make easier comparison between parts and it should suggest best-practice search criteria for parts selec- To attract customers, manufacturers should design tion. The goal of this paper is to show how these re- products that suit to various requirements. Custom- quirements may be fulfilled using the ISO 13584 ers become more and more exacting in their choices data model. and they want their products to have a different ap- The rest of this paper is organized as follows. In pearance from other ones. Manufacturers must de- section 2, we discuss the origin of product diversity. sign several variants of product. But designing vari- Various solutions to restrict diversity are presented. ants involve diversity. To reduce costs, Then we analyze the causes of parts diversity. In manufacturers must reduce diversity in products. section 3, we propose a new approach, i.e. creation One solution is to reduce the number of different of a single database. We discuss the advantages of parts. Indeed, a number of internal parts do not play such approach, and potential difficulties. We outline any role in the product appearance. Thus the number the PLIB model (ISO 13584) that would allow us to of parts which have the same functional use should create a database which would handle all presenta- be reduced. But we must first identify why designers tions of all information items. Tools may be de- cannot easily recognize parts which fulfill the same signed to generate various human-readable presenta- requirements. tions from this computerized representation. Section One reason seems to be that designers can hardly 4 presents a case study on fasteners in manufactur- compare various parts. Designers select their parts ing industry. We first discuss the context and then, from various sources (paper catalog, website, CAD we present different steps for the implementation of library, etc…). These sources often suggest different a PLIB database. Finally we show existing and in search criteria, thus different choice results. A possi- progress tools that can generate human-readable ble solution to this problem would be create a single presentations. database with a unique computerized representation of all the part information which would allow generation of all needed human-readable presentations. Database should allow to gather the various human- readable information items to be included in the various presentations like drawing or dimensional properties. Moreover, it must provide mechanisms to 2 THE DIVERSITY ISSUE 2.2.1 Standardization In the standardization approach, products are designed by using as much as possible the same existing parts. Consequently, the intermediate diversity

2.1 Product diversity origin decreases. Designers use tools that allow them to Manufacturers make products with low-cost per- search and select components that fulfill to their spectives and production profitability. Customers search criteria in a restricted set of components. want to buy products that meet as such as possible But using a smaller number of parts might de- their wishes. Two extreme scenarii exist. In the first crease the diversity of products, because we reduce one, a product fits to a large scope of customers. possibility to differentiate product from another one. One product with no options, thus no diversity, To keep final diversity, authorized components must matches with several needs because all functional- not prevent the differentiation of products. Profit- ities are integrated. This approach exists in electrical ability of this method depends on the balance be- domestic equipments. In the second scenario, manu- tween the cost of standardization and the profits re- facturers make one particular product for one par- sulting from economies of scale and reduction in ticular customer, like in space industry (e.g. satel- variety. Mathematical instrument was developed to lite). Automotive industries are in an intermediate find the best compromise (Lee, H.S. & Tang, C.S. state. They produce variants of car models in order 1997). to meet most customer needs. This approach requires a well-controlled diversity. 2.2.2 Modular design For automotive industries, product diversity ex- In the modular design approach, designers identify ists since the 50’s (Cialvaldini, C. & Loubet, J.L. repetitive units -elements or assembly of elements- 1995). Before these years, they used to make unique called modules. A module is designed with several products with little or no diversity. The Ford T functional capabilities and standard interfaces. Di- model from Ford Motor Company is the best exam- versity of functional capabilities allows using the ple (“People can have the Model T in any color so same module in several products: some functional long as it’s black”, Henry Ford). But after the 50’s, capabilities can be used in one product and not used came customized products. Some manufacturers in another one. Standard interfaces allow many con- created products with a number of variants and cus- figurations and permit interchangeability and inde- tomers could customize the product to fit with their pendence of modules. tastes. Then, this approach creates diversity of vari- To produce a large variety of products at lower ants. cost, one method to identify suitable modules has Diversity of variants is necessary to fit closely been proposed. It consists of using a matrix repre- with customer needs, whereas reducing diversity is sentation to model interactions between parts and essential to reduce manufacturing costs (manufactur- functions and to break down the matrix to identify ing approach versus marketing approach). That is elements as modules (Huang, C.C. & Kusiak, A. the diversity issue. Automotive manufacturers want 1998). Intermediate diversity decreases because to produce different variants of car models, with modules are defined with many functional capabili- several options or different bodies with the smallest ties and interfaces in order to replace several parts or number of different parts, in order to achieve two assembly of parts. As designers define modules with goals: meet all customer needs and produce enough several capabilities, product diversity may not de- to ensure profit. So they must define standardized crease and even more could increase it by using the elements or parts that they could use to design vari- new functional capabilities resulting from the mod- ous finished products. ule breakdown.

2.2 From the final diversity to the intermediate 2.3 Focus on parts diversity diversity In the previous section, we outlined two methods Reducing production costs by decreasing final diver- to reduce intermediate diversity. In this paper, we sity, i.e. variants diversity, is not an acceptable goal. focus on standardization of parts. But reducing the But, in several engineering design fields, products to part diversity may decrease the variants diversity. To be designed are essentially assemblies of technical avoid this drawback, we try to identify the useless elements. So it has been suggested to keep variants diversity that we define as the fact that two or more diversity and to decrease the internal diversity of parts fulfill the same requirement. To avoid this kind elements. Two approaches have been proposed: of useless part diversity, we must understand the standardization and modular design. reasons why two different designers may select two different parts for the same requirement. 3 DEFINING A DATA CENTERED APPROACH: The solution we suggest is to have both a single SWITCHING FROM DOCUMENT TO DATA computerized representation for each part but to of- fer several points of view on this information: several human-readable presentations of the same computerized representation. 3.1 Causes of parts diversity Therefore, our approach consists in building first The first cause of useless part diversity seems to be the (possibly distributed) database with all instances the diversity of the information processed by the and all properties about data, and second generating various actors. Several experts work on the design of presentations from this database for all the various product using tools adapted to their task like CAD disciplines, software tools and needed documenta- library for designers, FEA models for stress analysis tion.(Fig. 2). Presentations constitute various views engineers or paper catalogues and Web sites for of representations. buyers. There are as many sources of information as there are documents or parts representations (Fig. 1). When a tool is updated, each representation should Paper Catalogue be updated too in order to guarantee the integrity of data. Update operations are very costly and so they Website are often not performed. Thus information is fre- quently not accurate. CAD Components Library WebSite Database Database

Content of Common Catalogue Components

Computerised

CAD Library files

Figure 1: Difficulties with multi-sources of information generating Figure 2: Generating human-readable presentations Moreover, structure of information which allows users to select components are often different from Thus computerized representations to capture all one representation to the other. Designers search the part data need to be created in one place. The set parts according to the classification used in the rep- of points of view specific presentations is generated resentation. For CAD tools, designers search parts in automatically from this database. Moreover, the da- a tree-representation defining families of parts. In tabase structure shall allow to compare parts accord- paper catalog, parts are classified in family and users ing to their characteristic properties. must choose a part-family before selecting the part corresponding to their needs. Libraries are modeled 3.3 Use properties to reduce parts diversity as a hierarchy of parts, but as a rule the hierarchy depends on the point of view of the representation’s Moreover, to reduce the number of parts, we sug- author. Part retrieval is driven by the hierarchy struc- gest to define a property for each part with the value ture when it should be driven by the characteristics Recommended/Not Recommended. A part expert of the parts. will review the set of existing parts and selects those So we propose to make the same information which are recommended and those which are not available at the same time to all the actors of the ex- recommended. Substitution of not recommended tended enterprise by having only one computerized parts by recommended parts will decrease the num- representation of each part in one database and ber of different parts. This process becomes possible moreover, to facilitate selection by means of prop- when all the parts are accessible at the same time erty value, as independently as possible of the clas- and are described by the same properties. It is possi- sification structure. ble for instance when a not-recommended part is se- lected to display and suggest all the recommended parts which share the same property values. More- 3.2 From one computerized representation to over this can be done in each discipline specific several human-readable presentations presentation. But we cannot prescribe only one view on data. Ex- perts who work on products have their own back- 3.4 Obstacles ground and their own point of view on parts. It is impossible to create one part presentation structure Creating a single model for all information elements for all needs (design, financial, stress analysis…). existing in legacy representations is a real challenge. Different kinds of properties exist, like dimensional 3.5.1 Modeling of data parts family-the PLIB dic- properties or commercial properties shall. Moreover, tionary their integrity shall be guaranteed in particular by To define computer sensible parts library, we must ensuring that the same currency for prices or units identify which important items characterize existing for length and mass measures always assumed. Usu- libraries. In paper catalogues, suppliers expose their ally, each point of view-specific representation has lists of parts. A user selects a part according to the its own model and its own information structures. family he specifies or according to the value of a Commercial databases usually store information given part property. Nevertheless, the user must con- with a table-like structure. This computerized repre- sider the knowledge of the point of view the supplier sentation is common in most business-oriented ac- used in order to define the parts and the associated tivities. But in PDM (product data managers) sys- library. This knowledge is either processable (if it is tems, data are modeled by tree representations. computerized) from library. In paper catalogues, Rules help users to select parts by hiding some paths suppliers often describe categories of parts, their according to the selection query they have specified. properties and their classification. These concepts The unique computerized representation must feder- define supplier ontology. Thus, in order to get bene- ate all these data models and support in particular fits of all the concepts, computerized, parts library the same selection methods. Moreover, it must en- must supply this ontology information with the cata- sure properties integrity in their definition domain. logue content. Finally it should be able to associate with each part To handle such ontology, PLIB uses an informa- the various tool-specific presentation like CAD ge- tion model (Sardet, E. & Pierra, G. 1997), written in ometry models or marketing pictures. the EXPRESS language (ISO/IS 10303-11 1994, It is precisely what the PLIB model allowed us to Schenck, D. & Wilson P. 1994) and a methodology do. We summarize in the next clause the model ca- developed and published by IEC (the International pabilities. Electrotechnical Commission) and the ISO (Interna- tional Standard Organization). As example, IEC has developed a specific dictionary to define technical 3.5 The PLIB model properties and parts family for electrotechnical parts PLIB, for Parts Library, was a standardization initia- (IEC 61360-4 1997). Other dictionaries are under tive launched in the beginning of nineties. The PLIB development, especially one for fasteners (ISO/CD standard ISO 13584 permits to model parts library 13584-511 2002). data in computer sensible representation and enables PLIB dictionary (Pierra, G. 1994) allows to de- an unambiguous exchange of parts between suppli- fine a classification tree to identify families and ers and users. We can characterize the PLIB ap- properties and also information to qualify each part proach in four points: and each property. 1 This standard uses an object oriented approach A part family is identified through a unique code, for capturing supplier’s knowledge on parts; a version number, its author identification and other 2 PLIB is formally specified to guarantee inde- information like definitions, superclass and subclass. pendence between computer and software sys- The superclass gives a single inheritance tree and al- tems; lows hierarchical classification thanks to the is-a re- 3 PLIB separates the data model from the data it lationship. Technical properties fill up the definition. models. The data model is defined at the diction- A technical property is identified similarly with ary level, while data are stored at the content information like code, number of version, identifica- level. A dictionary is defined with a hierarchy of tion of the class where it was defined and other in- model classes and supports integration of multi- formation (translation, domain of values, symbol supplier libraries. Each supplier can define his …). Properties are classified in three families: own library with parts (a screw, a bolt, a cutting - Non dependent property: an invariable property tool …) and properties (screw diameter, bolt whose value is fixed once the part is defined. E.g. height, hardness of the cutting tool …). If several a screw’s diameter or a nut’s height; suppliers reference a common dictionary, librar- - Condition property: a context parameter whose ies with structures can be defined. value characterizes the part use condition. E.g. 4 The part definition and the part representations torque to screw parts in one sort of material; are separated. Representations have an independ- - Dependent property: a property whose value de- ent hierarchy of functional model class, linked to pends on condition property i.e. it is computed dictionary model classes by relationship related to from the depending on the values of a condition representation (view-of). This allow multi- property. representation (for drawing software or simula- To design a catalogue according to the PLIB ap- tion) of parts. proach, suppliers define a dictionary level before storing their part. So, they use the previous concepts to build a tree of classes and properties or they can reference an existing dictionary, thanks to the codes 4.1 Methodology of classes and/or properties. When referencing the Various documents, paper catalogues or intranet dictionary, suppliers can define their own parts hier- websites represent views of a same application do- archy by selecting parts families and properties used main (fasteners). Each support has its own classifi- in their catalogues. This relationship between the cation. Therefore various search methods according normalized dictionary and the supplier dictionary is to the used document have to be defined and mas- called is-case-of. If several suppliers define their tered. The diversity of the information points of own catalogues with the same dictionary, users can view has not been contested. But due to the hetero- compare them without ambiguity on knowledge. geneity, updates between the different formats are This is the basis of integration on federation of data handmade. This entails costs and delays, due to dif- in PLIB. ficulties to update parts information. The diversity of points of view leads to different structures and dif- Supplier A ferent definition formats as listed below. mass Screw diameter - Paper catalogues are generally written with MS length mass Machine screw word. The structure of these documents is presen- Fastener tation-oriented. Therefore parts information is Screw diameter Drilling screw length presented to be human-understandable. Parts Machine screw length families are followed by other parts families in

Drilling screw length order to build a list;

Nuts diameter - Intranet web sites use a similar approach. Infor- Fastener length mation is structured to be understandable for Stample Screw diameter readers. Parts families do not appear as a list but Nuts Dictionary diameter they appear as a tree displayed on a screen. Fami- Stample lies appear in the leaves of the tree; Supplier B - CATIA uses PDM (like Enovia VPM) as parts li- Figure 3: Dictionary with several catalogues brary. It is based on a tree-oriented structure different from the website tree structure; - Specific software like stress analysis tools uses 3.5.2 Modeling contents CSV files to load part’s definitions.

3.5.3 Modeling representations According to our previous presentation, PLIB sug- 4.2 Our approach gests to represent another hierarchy with functional Our goal is to evaluate the feasibility of a unique classes for storing tool-oriented presentation (Pierra, representation of all the necessary information. We G. 1993). A functional model class of the represen- propose to create a PLIB-oriented database and to tation hierarchy refers to one or several classes of generate, using an automatic processing, all the dis- the general model by the view-of relationship and al- cipline-specific presentations from this database. lows to represent technical models with several The use of one single database is important to con- points of view. Properties (non dependant, depend- solidate all part information in a single place. The ant and context properties) needed for the view are PLIB format allows to support the previously listed identified. Then, some attributes, called representa- representation structures and gives flexibility to de- tion attributes, are derived from model properties. fine the data model at the dictionary level. An object-oriented structuring is efficient to capture the part model. Moreover, the definition of properties al- 4 CASE STUDY: FASTENERS IN lows to give not only domain values but also units MANUFACTURING INDUSTRY for properties and other useful characteristics. Sepa- ration between a general model (representing part To illustrate the use of PLIB for reducing the di- families) and a functional model (representing pres- versity of data through integration and federation, a entations) facilitates the generations of presenta- case study was performed. In an automotive indus- tions. Moreover, the use of EXPRESS language try, designers search their fasteners in independent gives a neutral format from which several presenta- supports like paper catalogues, intranet websites, tions can be generated by automatic tools. CAD libraries for CATIA, specific software libraries So the development of a PLIB database requires to perform stress analysis, etc… A single part may is three steps: currently described on several supports. We tried to 1 Collecting information related to the knowledge centralize all fastener data in a single computerized on fasteners; representation using the PLIB data model. 2 Defining the fasteners ontology allowing to cate- STEP files in order to exchange PLIB libraries be- gorize the knowledge concepts, by using PLIB tween computers. But, how do we build the diction- model; ary? We suggest two approaches. 3 Designing tools for generation human-readable 1 Define our own dictionary. Each concept is de- and discipline-specific presentations of the set of fined during the first step and several documents fasteners. explain how structuring the data-model. Thus the These steps are described in details in the following dictionary meets our needs but nothing ensures subsections. that all fasteners manufacturers and users have the same concepts and definitions. 4.2.1 Collecting existing information on fasteners 2 Define our dictionary by referencing a normal- To collect the existing information on fasteners, in- ized existing dictionary like the one developed by formation in the automotive manufacturer item data- the CNIS (China National Institute of Standardi- base, in fastener suppliers’ catalogs and websites are sation) (ISO 13584-511 2002), which has pro- first considered. They contain families of fasteners, posed a fasteners dictionary, standardized at ISO but only dimensional properties are itemized. Spe- level according to PLIB concepts. Thus we can cific stress analysis software require also mechanical define our dictionary by referencing the CNIS properties for computation. We extracted them for dictionary. Technically, the case-of relationship, the software library. So, all the information elements defined in PLIB is used to support this referenc- about fastener existing in the company are now ing mechanism. gathered. We group all these information items on a single 4.2.3 Generating human-readable presentations support. We use MS Excel worksheets for the fol- As asserted in previous sections, PLIB based data- lowing reasons: base are stored in a neutral computer sensible for- - This software is available on most of the com- mat. Various presentations, essentially websites, pa- puter systems; per catalogues and CSV files, will be generated from - The structure of the worksheets gives a table like this PLIB database. structure. Facility for adding/removing columns allows us to add or remove properties; 4.2.3.1 Documents for the web - Sheets permit to do a first information structuring Web sites purpose is to show suppliers fasteners for separating the parts family (for example a family users. In most existing Web site, the document pre- per sheet); sented on the web site has some flaws. Indeed, if de- - The MS Excel software can save information un- signers search a family of parts in a tree, they find a der CSV (coma separated files) this format is ex- page in HTML or PDF format that shows all parts of ploitable by automatic tools. the family. They must read the whole page to select With this first step, information on fasteners is the part they are looking for. This document gives available in a computer format that may be under- nothing more than a paper catalogue. Information stood by human beings. All elements are centralized, within the documents is static. in a flexible structure that allows adding or remov- However, in a PLIB based approach, and thanks ing families and/or family properties. to the explicit modeling of information, it is possible to generate dynamic documents for the web from 4.2.2 Defining and modeling fasteners ontology PLIB database. A tool which is able to generate At this stage, all information about fasteners like: HTML webpage in order to put them on the web can families, properties and list of parts are consolidated. be defined. Moreover it is possible to enrich the The next step consists in associating a PLIB repre- document by dynamic information. Such a tool ex- sentation. Using PLIB concepts, the associated data ists. PLIB Browser takes a PLIB file and generates model will be defined at the dictionary-level (ISO an electronic document in DHTML (Dynamic Hy- 13584-42 1998) and the parts at the content level pertext Markup Language). With such a document, (ISO 13584-24 2002, ISO 13584-25 2003). The de- designers can select a part by evaluating some part sign of fastener dictionary is facilitated thanks to the properties. It is possible to select particular parts PLIB Editor tool. thanks to filters defined on properties instead of PLIB Editor is a JAVA application designed by reading a static document. the Laboratory of Applied Computer Science (LISI/ENSMA) for browsing, modifying and creat- 4.2.3.2 Paper documents ing a parts library according to the PLIB specifica- To search parts in paper catalog, designers use either tion. A data model or a dictionary is defined by us- summary (sums up the catalogue and follows its ing a hierarchy of classes and properties definitions. classification) or tables made to help selection. PLIB Windows display part in a table. User can input part data base content allow automatic generation of values or load CSV files issued from MS Excel or these documents. A tool called P21toXML generates any other software. PLIB Editor generates portable XML files from PLIB files that reflect the information structure as defined in PLIB (semantic tagging). Several steps were defined. The first step was to But the main advantage of paper documents is the group all information items about parts family and ordered and tree-structured presentation of informa- properties of parts defining the fasteners ontology. tion. The structure of object-oriented files used by In the next step, this information is put into PLIB PLIB is different from the structure of documents. format using the PLIB Editor tool. Then all the ex- Therefore, the PLIB approach proposes to define a isting presentations have been re-generated (with an document model using HTML tags. A Style sheet improved content) by an existing tool like PLIB written in XSLT takes the XML file and the HTML Browser. These tools are based on JAVA and use model and generates the HTML document. PLIB API to manage PLIB files and to produce the needed documents. 4.2.3.3 Specific files for software This approach, based on the PLIB technology, Specific software like stress analysis tools generally gives a whole methodology, supported by automatic use CSV files to load components model. Such tools tools which allow to centralize all relevant technical are used by designers to compute screws and bolts data for parts in a PLIB database. Moreover, tool- characteristics in an assembly. Users specify proper- specific representations (like CAD models) may be ties of the assembly with dimensional properties and attached. This approach has been validated on a non context constraints. Software selects screws and nuts trivial case study in manufacturing industry: the fas- corresponding to the parameters. Such tools need teners. specific internal representations of fasteners. A file format exists to allow updating of the tool library of fasteners. These files correspond to CSV files with 6 REFERENCES keywords identifying information. A tool that we developed takes PLIB files and generates files con- Cialvaldini, C. & Loubet, J.L. 1995, La diversité dans form to the software specification (i.e., using key- l’industrie française : Hésitations et enjeux. Regards croisés de l’historien et du gestionnaire. Gérer et comprendre n°41: words). 4-19. Another proposition will be to load PLIB files in IEC 61360-4 1997. Standard data element types with associ- such tools but we must modify each software. ated classification scheme for electric components - Part 4: Reference collection of standard data element types, com- ponent classes and terms. Geneva: ISO. 5 CONCLUSION ISO/IS 10303-11 1994. Industrial automation systems and integration - Product data representation and exchange - Part 11: Description Methods: The EXPRESS Language The purpose of this paper is to contribute to reduce reference manual. Geneva: ISO. the diversity of parts in the manufacturing industry. ISO 13584-24 2002. Industrial automation systems and inte- We have first identified one cause of part diversity: gration - Parts Library – Part 24: Logical Model of Sup- the diversity of part description and their content plier Library. Geneva: ISO. ISO 13584-25 2003. Industrial automation systems and inte- heterogeneity. Each description is a stand alone rep- gration - Parts Library – Part 25: Logical model of sup- resentation and needs to be updated by users using a plier library with aggregate values and explicit content. handmade approach. As a consequence all the hu- Geneva: ISO. man-readable presentations of these descriptions are ISO 13584-42 1998. Industrial automation systems and inte- not at the same updating state. Moreover, some parts gration - Parts Library – Part 42: Methodology for Struc- appear only on some descriptions and not on the turing Parts Families. Geneva: ISO. ISO/CD 13584-511 2002. Industrial automation system and in- others. Each description suggests its own selection tegration — Parts library— Part 511: Mechanical Systems methods and can not allow powerful comparison be- and Components for General Use —Reference Dictionary tween parts. for Fasteners. Geneva: ISO. We propose to create a single computerized rep- Huang, C.C. & Kusiak, A. 1998. Modularity in design of prod- resentation of each part within a database. This data- ucts and systems. IEEE Transactions on Systems, Man and Cybernetics, Part A: Systems and Humans, vol. 28, N°1: base is based on the PLIB data model which defines 66-77. all the useful mechanisms to capture all the aspects Lee, H.L. & Tang, C.S. 1997. Modelling the costs and benefits of a part description in computer sensible representa- of delayed product differentiation. Management Science, tion. Its standard format allows to generate any kind vol. 43(1): 40-53. of human-readable presentations with tools like the Pierra, G. 1993, A Multiple Perspective Object Oriented Model generation of DHTML document by PLIB Browser. for Engineering Design. New Advances in Computer Aided Design and Computer Graphics, International Academic We have presented the implementation of our Publishers. Beijing : 368-373. proposal through a case study: the management of Pierra, G. 1994, Modelling classes of pre-existing components fasteners in some manufacturing industry. Before in a CIM perspective: the ISO 13584 / ENV 400014 ap- our study, there were no description (document or proach, Revue internationale de CFAO et d’Infographie, whatever) that contained all the information on the vol.9: 435-454. Pierra, G. & Potier, J.C. & Sardet, E. 2003, From Digital Li- used fastener. Each document has its own list of braries to Electronic Catalogues for Engineering and Manu- parts and some parts appear only in one document. facturing. International Journal of Computer Applications in Technology (IJCAT) vol. 18: 27-42. Sardet, E. & Pierra, G. 1997. Formal specification, modelling and exchange of classes of components according to PLIB. A case study. Proceeding of global Network Engineering 97. Antwerp:179-201. Schenk, D. & Wilson, P. 1994. Information Modelling The EXPRESS Way London: Oxford University Press.