Product Modelling Using Multiple Levels of Abstraction_612045

8/13/2019 Product Modelling Using Multiple Levels of Abstraction_612045

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18 F . E r e n s e t a l, / C o m p u t e r s in l n d u s t o 2 4 ( 1 9 9 4 ) 1 7 - 2 8b e s t c h a r a c t e r i z e t h i s c l a ss o f s p e c i a l i z e d a p p l i c a -t i o n s a r e :- T h e i r s t r u c t u r a l d a t a ( d a t a d e s c r i p t i o n , d a t a

i n t e r r e l a t i o n a n d d a t a c l a s s i f i c a t i o n ) i s t y p i c a l l ym o r e d y n a m i c t h a n c o n v e n t i o n a l d a t a -i n t e n s iv ea p p l i c a t i o n s a n d is i n t e r t w i n e d w i t h , a n d o f t e na p a r t o f , t h e r e p e t i t i v e d a t a i t s e l f .

- T h e a m o u n t o f s t r u c tu r a l i n f o r m a t i o n i s l a rg ec o m p a r e d t o t h e s i m p l e i n f o r m a t i o n c o n t e n t ,f o r e x a m p l e t h e g e o m e t r y d e s c r ip t i o n o f a t r u c kis h ig h l y s t r u c t u r e d a n d i n c l u d e s a r e l a t iv e l ys m a l l a m o u n t o f re p e t i t i v e d a t a .

- E n d - u s e r s h a v e d i f f e r e n t v i e w s o n t h e s a m ed a t a . S o m e a r e w o r k i n g o n p r o d u c t f a m i l ys t r u c t u r e s , o t h e r s o n d e t a i l e d c o m p o n e n t d e -s c r ip t i o n s , a ll u s in g t h e i r o w n t e r m i n o l o g y a n da p p l i c a t io n s . W h a t t h e y h a v e i n c o m m o n i st h a t t h e u s e r s a r e s t r o n g l y c o n n e c t e d w i t h th ed a t a . B r o w s i n g t h e d a t a b a s e s e e i n g t h e s t ru c -t u r e a s w e l l a s t h e r e p e t i t i v e d a t a i s a n i m p o r -t a n t a s p e c t o f t h e i r w o r k . T r a d i t i o n a l b u s i n e s sa p p l i c a t i o n s h a v e r i g i d u s e r i n t e r f a c e s t o s h e l -t e r t h e u s e r f r o m t h e s t r u c t u r e o f t h e d a t a b a s ei t se l f .A p p l i c a t i o n s w h e r e s t r u c t u r a l d a t a i s i n t e r -

t w i n e d w i t h r e p e t i t i v e d a t a o f t e n e n c o u n t e r am o d e l l i n g p r o b l e m w h e n t r a d i t i o n a l d a t a b a s et e c h n o l o g y i s a p p l i e d . D e s i g n c h o i c e s m u s t b em a d e a b o u t w h i c h p a r t o f t h e d a t a is s e e n a ss t r u c tu r a l a n d m o d e l l e d i n th e d a t a b a s e s c h e m a ,a n d w h i c h p a r t o f t h e d a t a is s e e n a s r e p e t i ti v ea n d m o d e l l e d i n th e d a t a b a s e a s o c c u r r e n c e s o ft h e d a t a b a s e s c h e m a . H o w e v e r , a c l o s e r l o o k a tt h e s e a p p l i c a t i o n s r e v e a l s t h a t t h e r e i s a s l i d i n gs c a le b e t w e e n s t r u c t u r a l d a t a a n d r e p e t i t i v e d a t a .I t i s n o t a l w a y s p o s s i b l e t o s p l i t t h e d a t a i n t o t w od i s t i n c t i v e g r o u p s . T h i s s t a t e m e n t i s e l u c i d a t e d i nt h e n e x t s e c t i o n w i th a n e x a m p l e o f d e v e lo p i n gp r o d u c t f a m i l i e s .

T h e r e m a i n d e r o f th i s p a p e r is o r g a n i z e d a sf o l l o w s . I n S e c t i o n 2 w e i n t r o d u c e a s i m p l e e x a m -p l e w i t h a r e l a ti v e l y d y n a m i c s t r u c t u r e a n d l im -

i t e d q u a n t i t i e s o f d a t a . S e c t i o n 3 is u s e d t o d e -s c r ib e t h e m u l t i p l e l e v el s o f a b s t r a c ti o n . T h e n , i nS e c t i o n 4 , o u r c u r r e n t i n s i g h t s i n t o m o d e l l i n gm u l t i p l e l e v el s o f a b s t r a c t io n a r e s u m m a r i z e d .O u r s o l u t i o n t o t h e p r o b l e m i s d e s c r i b e d i n S e c -t i o n 5 w i t h t h e L e e d s P r o d u c t D a t a E d i t o r . F i -n a l l y s o m e c o n c l u s i o n s a n d p o s s i b i l i t i e s f o r f u r -t h e r r e s e a r c h a r e p r e s e n t e d .

2 An example: Produ ct family mo del l ingT h e c h a n g e f r o m t h e s e l le r s m a r k e t o f t h e

f i ft i es t o t h e b u y e r s m a r k e t w e k n o w t o d a y h a sr e s u l t e d i n a d r a m a t i c i n c r e a s e o f p r o d u c t v a ri -a n t s . W h e r e p r o d u c t s w e r e o r i g i n a l l y o f f e r e d i no n l y a fe w v a r i a n t s , n o w s o m e p r o d u c t s c a n b ep r o d u c e d i n m i l l i o n s o f ( s l i g h t l y ) d i f f e r e n t v a r i -a n t s . E x a m p l e s c a n b e f o u n d i n c a r , a e r o p l a n ea n d m e d i c a l e q u i p m e n t c o m p a n i e s . I n t h e s e s i t u -a t io n s , i t is n o t e c o n o m i c a l l y v i a b l e a n y m o r e t om a k e a l l v a r i a n t s t o s t o c k .

I t i s d i f f i c u l t t o s t o r e a l l p o s s i b l e v a r i a n t s s e p a -r a t e l y i n a d a t a b a s e b e c a u s e o f t h e d a t a r e d u n -d a n c y c a u s e d b y th e c o m m o n a l i ty b e t w e e n t h ev a r i a n t s . F u r t h e r , i t is d i f f i c u l t t o h a v e i n s i g h t i n t ot h e f a m i l y o f v a r i a n t s a s t h e r e l a t io n s h i p s b e -t w e e n t h e v a r i a n t s ( i. e. t h e s t r u c t u r e o f t h e f a m -i ly ) a r e n o t s t o r e d i n t h e d a t a b a s e a n d t h u s l o s tf o r th e u s e r a n d e v e r y o n e e ls e . T h e r e f o r e , b o t h an e w f a m i l y d e s c r ip t i o n a n d a n e w l o g i st ic c o n c e p ti s n e e d e d :- p r o d u c t f a m i l ie s s h o u l d b e d e s c r i b e d a s p r o d -

u c t f a m i l i e s , i n s t e a d o f a c o l l e c t i o n o f i n d i v i d -u a l p r o d u c t v a r i a n t s; a n d

- c u s t o m e r s s h o u l d b e a b l e t o s p e c if y a v a r i a n to f a p r o d u c t f a m il y, a n d t h e m a n u f a c t u r e rs h o u l d b e a b l e t o a s s e m b l e t h a t s p e c i f i c variantt o c u s t o m e r o r d e r .T h e c u s t o m e r s p e c i fi c a t io n , t o g e t h e r w i t h a

p r o d u c t f a m i l y d e s c r i p t i o n , i s u s e d t o g e n e r a t e a ll

Product Var ian tDescription is function ofus tomerSpecification

F i g 1 G e n e r a t i n g p r o d u c t in f o r m a t i o n

nd the Product Fam i lyDescription


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F. Erens et al . / Com puters in Industry 24 1994) 1 7-2 8 19

F i g 2 P r odu c t f a mi l y s t r uc t u r e

specific (manufacturing) documentation for thatspecif ication (Fig. 1) [2].In order to enable the generation of a productvariant description, specifically for a given cus-tomer specification, a product family descriptionmust be available. The creation of such a familydescription is normally the responsibility of mar-keting, engineering and design. It is an exampleof data where structural data is intertwined withrepetitive data and shared between differentusers.xample

Consider, for example, a car family. A car is,amongst other things, assembled from a chassis,an engine, a gearbox and an interior. The interioris assembled from the seats and the dashboard(see Fig. 2). The relationships between the differ-ent parts of the car are structural data, while theparts themselves are repetitive data which mayitself be structured.

Further, a number of views can be determined,each having its specific requirements in the orga-nization. The design process of such a car in-volves two d ifferent types of activity and producesdata on different abstraction levels, namely:- structural data , shared by all cars of thatfamily which defines the structure of a car;- r e p e t i t i v e data , which details the compo-nents of a car.These different abstraction levels will be eluci-dated in the next section. First we will continuewith this example.

Each of the aforemen tioned sub-assemblies canbe considered as a product family. The interior,for example, is a product family which is assem-bled from the seats and the dashboard. All prod-

uct families have a number of variants. The vari-ety of the car family originates from the variety ofits sub-assemblies. In turn, the variety of theinterior originates from its sub-assemblies, i.e. ofthe seats and the dashboard.

The data structures behind today's engineeringdatabases [3,4] typically necessitate the definitionof every variant of a product family. This meansthe need for the separate description of possiblymillions of variants of a car, where each descrip-tion has a large commonality with descriptions ofother variants. This redundancy of data is nor-mally not acceptable.When variants of a product family are physi-cally assembled from component variants, it ispossible to build the descriptions of the variants.The description of a car variant can be builtfrom:- the descriptions of the chassis, engine, gearbox

and interior variants; plus- the description of the car family (e.g. how dothe component families fit together).For example, the description of an interior

variant can be built from the descriptions of theseat and dashboard variants, plus some informa-tion about interiors in general (e.g. how seat anddashboard families are normally assembled). Fig.3 shows the built descriptions in black and thebasic descriptions in white. Basic descriptions be-long to basic, or so-called primary variants, whilebuilt descriptions belong to so-called assemblyvariants.

For the purpose of this paper, we will assumethat all assemblies are assembled to customerorder. The generation of product descriptions for

F i g 3 B u i l d i n g d o c u m e n t a t i o n o f a s s e m b l e d v a r ia n t s


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211 F . Eren s e t a l . / Com puter s in Indus try 24 1994) 17--28T a b l e 1P a r a m e t e r s a n d p a r a m e t e r v a l u e s f o r th e e n g i n eP a r a m e t e r s P a r a m e t e r v a l u e sE n g i n e s i z e 1 . 8 l i t re 2 . 0 l i t r eT u r b o y e s n o

v a r i a n t s i s in l i n e w i t h t h e n a t u r e o f a s s e m b l e - t o -o r d e r m a n u f a c t u r i n g . B o t h p h y s i c a l s t o c k s a n dd a t a r e d u n d a n c y a r e r e d u c e d .

I n r e p e t i t i v e s i t u a t i o n s , w e d o n o t w a n t t ob u i l d t h e d e s c r i p t i o n s o f t h e i n d i v id u a l p r o d u c tv a r i a n ts b y h a n d . P r e f e r a b l y w e w a n t t o g e n e r a t ea ll o f t h e n e c e s s a r y i n f o r m a t i o n a u t o m a t i c a l l yf r o m t h e c u s t o m e r o r d e r , a s s h o w n i n F i g . 1 .T h e r e f o r e w e n e e d t o in t r o d u c e a d e fi n i n g m e c h -a n i s m w h e r e c u s t o m e r s c a n d e s c r ib e a p r o d u c tv a r i a n t i n c o m m e r c i a l t e r m s a n d m a n u f a c t u r i n gc a n d e s c r i b e a p r o d u c t v a r i a n t i n t e r m s o f t h ep r o d u c t a r c h i t e c t u r e a n d t h e p r i m a r y v a ri a n t sf r o m w h i c h t h e o t h e r v a r ia n t s a r e c o m p o s e d . T h i sm e c h a n i s m i s c a l l e d a g e n e r a t i v e b i l l - o f - m a t e r i a l[5].

T h e c o m m e r c i a l t e r m s i n w h i c h a c u s t o m e rs p e c i f i e s a p r o d u c t v a r i a n t a r e c a l l e d p a r a m e t e r s .E a c h p a r a m e t e r h a s a n u m b e r o f p o s s ib l e v a l u e sf r o m w h i c h t h e c u s t o m e r m u s t c h o o s e t o d e f i n e ap r o d u c t v a r i a n t. W e w il l n o t e l a b o r a t e o n t h i ss u b j ec t , b u t t h e p a r a m e t e r s t h a t a r e r e l e v a n t tos p e c i f y t h e e n g i n e a r e l i s t e d i n T a b l e 1 , a s w e w i l lu s e t h e s e p a r a m e t e r s i n S e c t io n 4 .

3 M u l t ip le l eve l s o f abs trac t ion

I n t h e p r e v i o u s s e c t i o n , w e i n d i c a t e d t h a t t h e r ea r e t w o d i f f e r e n t a s p e c ts t o t h e d e s i g n o f p r o d u c tf a m i li e s , n a m e l y , d e f i n i n g t h e s t r u c t u r e o f t h ep r o d u c t f a m i l y a n d d e t a il i n g t h e c o m p o n e n t v a r i-a n t s t h a t c a n o c c u r i n t h i s s t r u c t u r e .

A n e n g i n e e r w h o is r e s p o n s i b l e f o r d es i g n i n gc a r s i n g e n e r a l w i l l u s e a d a t a b a s e t o f a c i l i t a t e h i so r h e r d e s i g n a c t i v i t i e s . T h e s e a c t i v i t i e s h a v e , f o ra l a r g e p a r t , a p r o j e c t m a n a g e m e n t c h a r a c t e r .

T h e i n f o r m a t i o n s t r u c t u r e t h a t s ) h e n e e d s f o rd e s i g n i n g c a r s w i l l b e i m p l e m e n t e d i n t h ed a t a b a s e s c h e m a a n d w i l l c o n t a i n e n t i t i e s l i k e :- w h o is r e s p o n s i b l e f o r a p r o d u c t f a m il y ;- w h e n i t s d e t a i l e d d e s i g n s h o u l d s t a r t a n d f in -

ish;- t h e r e l a t i o n s h i p s w h i c h e x is t w i t h o t h e r p r o d -

u c t f a m i l i e s ; a n d- w h e r e t h e v a r i a n ts o f a c e r t a i n p r o d u c t f a m i ly

w i l l b e m a n u f a c t u r e d .A s p e c i f i c c a r f a m i l y w il l b e s t o r e d i n a

d a t a b a s e , u s i n g s u c h a d a t a b a s e s c h e m a . W h e nt h e d a t a d i c t i o n a r y i s l e v e l 1 i n t h e l i s t o f a b s t r a c -t i o n l ev e ls , t h e n t h e d a t a b a s e s c h e m a f o r t h ep r o j e c t m a n a g e m e n t o f c a r d e v e l o p m e n t w il l b el e v e l 2 , a n d t h e i n d i v i d u a l f a m i l i e s w i l l b e f o u n do n t h e t h i r d l e v e l .

O t h e r p e o p l e a r e r e s p o n s i b l e f o r d e f i n in g t h ep o s s i b l e v a r i a t i o n i n t h e p r o d u c t f a m i l i e s w h i c hc o n s t i t u t e t h e c a r r a t h e r t h a n t h e a r c h i t e c t u r e o ft h e c a r i t s e l f : f o r e x a m p l e , t h e g e a r b o x , t h e f u e li n j e c t o r a n d t h e s e a ts . T h e p o s s i b l e v a r i a t io n o f ap r o d u c t f a m i l y i s d e f i n e d b y a l i s t o f f a m i l y -s p e c if ic p a r a m e t e r s . F o r e x a m p l e , a n e n g i n e m a yb e d e f i n e d b y i t s s i z e a n d w h e t h e r o r n o t i t i st u r b o - c h a r g e d w h e r e a s a s e a t m a y b e d e f i n e d int e r m s o f it s m a t e r i a l , d e g r e e o f p a d d i n g a n d t y p eo f h e a d r e s t . F o r t h e s e p e o p l e t h e p a r a m e t e r s o fe a c h p r o d u c t f a m i l y s h o u l d b e c a p t u r e d i n ad a t a b a s e s c h e m a s o th a t v a r i an t s c a n b e d e f i n e di n a d a t a b a s e w h i c h c o n f o r m s t o t h i s s c h e m a .

T h u s , i n t o ta l , f o u r l e v e l s o f a b s t r a c t i o n c a n b ed e t e r m i n e d i n o u r e x a m p l e :1 ) t h e d a t a - d i c t i o n a r y l e v e l is a d a t a s t r u c t u r e ;2 ) t h e p r o j e c t m a n a g e m e n t l ev e l s u p p o r t s t h e

d e s c r i p t i o n o f p r o d u c t f a m i l ie s ;3 ) p r o d u c t f a m i l i e s a re d e f i n e d i n t e r m s o f t h e

p r o j e c t m a n a g e m e n t d a t a s t ru c t u r e s a n d d e -f i n e t h e s e t s o f p a r a m e t e r s i n t e r m s o f t h e i rv a r i a n t s w h i c h m u s t b e d e f i n e d ;

4 ) p r o d u c t v a r i a n t s a r e d e f i n e d i n t e rm s o f t h e i rf a m i l y p a r a m e t e r s .

T h e s e f o u r l e v e ls a re s u m m a r i z e d i n F ig . 4. I tc a n b e s e e n t h a t l e v el s 1 a n d 2 a re d a t a s t r u c t u r e sa n d t h a t l e v e l 4 is i n s t a n c e d a t a . H o w e v e r , l ev e l 3i s b o t h a d a t a s t r u c t u r e w h e r e t h e f o r m o f v a r i -a n t s is d e f i n e d ) a n d a n i n s t a n c e o f t h e p r o j e c ts t r u c t u r e f o r a c a r f a m i l y ) .


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F. Eren s et al . / Com puters in Industry 24 1994) 1 7-2 8 21

project structure o~rep~

produ ct fam ilies ~mp~e

product var iants exara ~

data-dictionary

c a r developmentIn~ce-of

gearbox

gearbox G1.8

~ Instance-oengine

~ I rr s t a n c e o fengine E1.8t

Fi g . 4 , Exa m pl e s o f c l a s s i f ic a t i on .

level 1

level 2

level 3

level 4

Limitations of conventional database systemsRedundancy of data is introduced when theseabstraction levels are implemented in separatethree-layer databases:

The first type of redundancy concerns the dif-ferent abstraction levels. It is not possible tomodel four levels of abstraction without repeatingstructural data in one database as repetitive datain another database. Conventional relational orobject-oriented databases have only three levels,namely: data dictionary, tables/classes and tu-pies/instances.

The second type of redundancy concerns re-dundancy within a single level. Database tables(for example for variants of the engine and thegearbox) will have a number of similar attributes,which are repeated for tables. An example isgiven in Section 4.1.

The next section describes how today's tech-niques deal with the modelling of abstractionlevels and data redundancy in general. It is shownthat even modern object-oriented databases arenot powerful enough to model this problem con-ceptually right. More advanced, but still aca-demic, approaches offer better solutions.

4 C u r r e n t p r a c t ic e s a n d in s i g h t sIn this section, we will describe three differentapproaches before we elaborate a fourth ap-

proach, which is based on the Leeds ProductData Editor, in Section 5. Firstly, we will discussan implementation in a relational database. Sec-ondly, we will describe the advantages and short-comings of object-oriented databases. Finally, wewill show a fundamentally different approach(3DIS) which has been proposed by Afsarmaneshand McLeod [1].4 1 Relational approach

Relational databases make a clear distinctionbetween data and structure [6]. Normally, there isa large volume of data and only a relatively smalland stable structure. This structure is often calledthe database schema and is used by applicationprogrammes to work on the data. According toour previous figure, we will need a number ofdifferent, however related databases:- car development as a project database for

specific product families (see Table 2);-several databases for product families, e.g.engine and gearbox (see Tables 3 and 4).

From this example, it can be seen that en-gine and gearbox appear both on the datalevel (Table 2), and on the schema level (Tables 3and 4).

In this way data redundancy over differentlevels of abstraction is introduced. Further, theengine (gearbox) information that is presented inTable 2 is valid for all design variants of thatengine (gearbox) which can be found in Table 3

T a b l e 2A t t r i b u t e s a n d d a ta f or c a r d e v e l o p m e n tP r o d u c t f a m i l y R e s p o n s i b i l i ty F a m i l y s t a r t F a m i l y f i n is h M a i n p r o d u c t r e l a t i o n s h i p sn a m e d a t e d a t eCa r P . B r e u l s 1992 - 10 1995 - 2 Eng i ne , Ge a r bo xEn g i ne H . He gge 1993 - 3 1994 - 8 I gn i t i on , Ge a r bo xGe a r bo x E . P l a t i e r 1993 - 3 1994 - 6 I n t e r i o r , En g i neI n t e r i o r R . S t e ke l 1993 - 7 1994 - 11 Da s hb oa r d , Se a t sCha s s i s T . Re nk e m a 1992 - 10 1993 - 12 I n t e r i o r , Sus p e ns i on


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22 F . E r e n s e t a l. / C o m p u t e r s i n I n d u s t r y 2 4 1 9 9 4 ) 1 7 - 2 8Table 3Attributes and data for the product family 'engineDesign Fuel Gearbox Variant Commercial paramete rsvariant economy interface start dateEl .8 16 km / l G1.8 1993-3 engin e size = 1.8 and tur bo = noE2.0 18 km / I G2.0 1993-4 engin e size = 2.0 and turbo = noEl. St 15 km / l G1.8 1993-8 engin e size = 1.8 and tur bo = yesE2.0t 17 km / l G2.0 1993-9 engine size = 2.0 and tur bo = yes

Table 4Attributes and data for the product family gearboxDesign Gear Propeller shaft Variant Commercial paramet ersvariant ratio interface start dateGI. 8 1:0.5678 S-manual 1993-4 engine size = 1.8 and automat ic = noG 1.8a 1:0.6201 S-autom atic 1993-4 engin e size = 1.8 and aut omat ic = yesG2.0 1:0.7675 S-ma nual 1993-10 engi ne size = 2.0 and aut omat ic = noG2.0a 1 : 0.8945 S-automa tic 1993-10 engi ne size = 2.0 and auto mati c = yes

( T a b l e 4 ) . I t i s h o w e v e r n o t p o s s i b l e t o e x p r e s st h e l i n k b e t w e e n t h e e n g i n e ( g e a r b o x ) t u p l e o fT a b l e 2 a n d t h e d a t a b a s e s c h e m a o f T a b l e 3( T a b l e 4 ) .

T h i s c o m p l e x i t y is f u r t h e r i n c r e a s e d d u e t or e d u n d a n c y o f s t r u c t u ra l i n f o r m a t i o n w i t h in as i n g le l e v e l o f a b s t r a c t i o n . T h e a t t r i b u t e s v a r i a n ts t a rt d a t e a n d c o m m e r c i a l p a r a m e t e r s , f o re x a m p l e , a r e n e e d e d b y b o t h t h e e n g i n e a n d t h eg e a r b o x t a b l e ( o n le v e l 3 ), a n d a r e r e p e a t e d f o rb o t h . H o w e v e r , n o t o n l y t h e a t t r i b u t e s a r e r e -p e a t e d , a l s o t h e a p p l i c a t i o n p r o g r a m m e s w o r k i n go n t h e s e a t t r i b u t e s e i t h e r :- a r e d u p l i c a te d a n d a d a p t e d f o r t h e d i f f e re n t

t a b l e s i n w h i c h t h e s e a t t r i b u t e s o c c u r ; o rk n o w a b o u t b o t h d a t a b a s e s c h e m a ( t h e e n g i n ea n d t h e g e a r b o x s c h e m a ) .B o t h s i t u a t io n s m a k e a n a d a p t a t i o n o f t h e

d a t a b a s e s c h e m a m o r e d i ff i cu l t a n d c o st ly . T h en e x t s e c t i o n s h o w s h o w o b j e c t - o r i e n t a t i o n u s e si n h e r i t a n c e t o r e m o v e t h is r e d u n d a n c y w i th i n as i n g l e l e v e l o f a b s t r a c t i o n . T h e r e d u n d a n c y o v e rd i f f e r e n t l e v e ls o f a b s t r a c t i o n , h o w e v e r , c o n t i n u e sto e x i s t .

4.2. Object or iented approachA l t h o u g h o b j e c t - o r i e n t e d t e c h n i q u e s [7 ] o f f e r

s o m e p o w e r f u l c o n c e p t s f o r d a t a m o d e l l i n g , t h e r e

i s s t i l l a g e n e r a l c o n s e n s u s t h a t t h e r e i s a s t r i c tb o r d e r l i n e b e t w e e n s t r u c t u r a l d a t a ( c l a s s e s ) a n ds p e c i f i c d a t a ( o b j e c t s ) . I n s t a n t i a t i o n i s u s e d t ol i n k t h e c l a ss a n d o b j e c t l e v e l s a n d c a n b e r e -g a r d e d a s t h e m o s t b a s i c o b j e c t - o r i e n t e d r e u s a b i l -i ty t e c h n i q u e a s o b j e c ts r e u s e t h e s t r u c t u r e w h i c hi s d e f i n e d a t t h e i r c l a s s e s . C l a s s e s c a n b e r e -g a r d e d a s i n s t a n c e s o f a m e t a - c la s s , w h i c h i ss i m i l ar t o t h e d a t a d i c t i o n a r y o f re l a t i o n a ld a t a b a s e s . W i t h r e s p e c t t o d i f f e r e n t a b s t r a c t i o nl e v e l s , t h o u g h , t h e d a t a r e d u n d a n c y i s n o t s o l v e d .

I n S e c t i o n 4 . 1 , w e d i s c u s s e d t h e p r o b l e m o fr e d u n d a n c y a t t h e s t r u c t u r a l l e v e l . A t t r i b u t e sn e e d t o b e r e p e a t e d a s w a s s h o w n i n T a b l e 3 ,w h e r e s o m e a t t r i b u t e s ( d e s i g n v a r i a n t , v a r i a n ts t a rt d a t e a n d c o m m e r c i a l p a r a m e t e r s ) a r e n o tu n i q u e f o r a n e n g i n e a n d t h e r e f o r e r e p e a t e d f o rt h e g e a r b o x i n T a b l e 4 . A n o b j e c t - o r i e n t e d t e ch -n i q u e t o r e m o v e t h i s d a t a r e d u n d a n c y i s t h e u s eo f s t r u c t u r a l i n h e r i t a n c e . A t t r i b u t e s a n d a p p l i c a-t i o n p r o g r a m m e s t h a t a r e s h a r e d b y s e v e r a l c l a ss e sa r e o n l y d e f i n e d o n c e a n d t h e n i n h e r i t ed t o th e s ec l a s s e s . T h i s m e c h a n i s m i s a l s o k n o w n a s s p e c i a l -i z a ti o n o r t h e s u p e r c l a s s / s u b c l a s s r e l at i o n s h ip[ 7]. F i g . 5 s h o w s h o w t h e a t t r i b u t e s d e s i g n v a r i-a n t , v a r i a n t s t a rt d a t e a n d c o m m e r c i a l p a -r a m e t e r s a r e i n h e r i t e d f r o m a s u p e r c l as s

f a m i l y . T h e s e a t t ri b u t e s o n l y n e e d t o b e d e -f i n e d o n c e, a n d c a n t h e n b e m a d e u s e o f b y a n ys u b c l a ss o f f a m i l y .


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F. Erens et al . / Computers in Industry 24 1994) 17 -28 2 3

nginf m i ly ~ o ~ ~

comm erdal parametorsde inn v dan tvlulont mld ditom m m o ~ a d Bo w r m a opm p imiift InCwface

F i g . 5 . I n h e r i t a n c e o f s t r u c t u r a l i n f o r m a t i o n .

4 .3 . 3DI S approachA f s a r m a n e s h a n d M c L e o d [1 ] p r o p o s e a

d a t ab as e w h e r e a l l i n f o r m a t i o n i n c l u d i n g t h e d a t a ,t h e d e s c r i p t i o n s an d c l a s s i f ic a t i o n s o f d a t a( m e t a - d a t a ) , ab s t r ac t i o n s , o p e r a t i o n s , an d co n -s t r a i n t s a r e t r e a t ed u n i f o r m l y a s o b j ec t s . W i t h i nt h i s f r am ew o r k , 3 D I S i n co r p o r a t e s s ev e r a l p r ed e -f ined abs t r ac t ion pr imi t ives , inc lud ing a genera l -i za t ion h ie rarchy .

O b j e c t s a n d m a p p i n g s a r e t h e t w o b a s i c m o d -e l l i n g co n s t r u c t s i n 3 D I S . R e l a t i o n s h i p s am o n go b j e c ts a r e m o d e l l e d b y ( d o m a i n - o b j e c t, m a p -p i n g - o b j ec t, r an g e - o b j ec t ) t r ip l e s . T h e s t r u c t u r eo f t h e s e t r ip l e s i s v e r y m u ch l ik e t h e b i n a r y r e l a -t i o n s h ip s i n t h e b i n a r y s em an t i c m o d e l [ 8 ]. B e l o ws o m e m ap p i n g s a r e g i v en , w h i ch a r e u s ed f o r t h eca r ex am p l e i n F i g s . 6 - 8 :M e m b e r / t y p e m a p p i n g s- i n s t a n t i a t i o n : H a s - m e m b e r : t y p e o b j e ct sP ( a t o m i c / c o m p o s i t e o b j e c t s )- c l as s if i ca tion : ( I s - a -m em ber -o f )M e m b e r - m a p p i n g / t y p e m a p p i n g s- d e c o m p o s i t i o n : H a s - m e m b e r - m a p p i n g : t y p eo b j e c t s ~ P ( m e m b e r - m a p p i n g s )

ag g r eg a t i o n : ( I s - a - m em b er - m ap p i n g - o f )P r o d u c t , H a s - m e m b e r - m a p p i n g , {

H a s - p r o d u c t - f a m i l y - n a m e ,H a s - r e s p o n s i b i l i t y ,H a s - f a m i l y - s t a r t - d a t e ,H a s - f a m i l y - f i n i s h - d a t e ,H a s - m a i n - p r o d u c t - r e l a t i o n s h i p s } )F i g . 6 . C a r d e v e l o p m e n t l e v e l .

E n g i n e , H a s - m e m b e r - m a p p i n g , { H a s - d e s i g n - v a ri a n t ,H a s - f u e l - e c o n o m y ,H a s - g e a r b o x - i n t e r f a c e ,H a s - v u r i a n t - s t a r t - d a t e ,H a s - c o m m e r c i a l - p a r a m e t e r s } )

E n g i n e , I s - a - m e m b e r - o f , { P r o d u c t } )C o m m e r c i a l - p a r a m e t e r s , H a s - m e m b e r - m a p p i n g , { H a s - n a m e ,

H a s - v a l u e } )E n g i n e , H a s - r e l a t e d - p r o d u c t , { I g n i t i o n } )E n g i n e , H a s - r e l a t e d - p r o d u c t , { G e a r b o x } )E n g i n e , H a s - m e m b e r , { E l . 8 ,

E 2 . 0 ,E 1 . 8 t ,E 2 . 0 t } )F i g . 7 . E n g i n e d e f i n i t i o n l e v e l .

E v e r y i d en t i f iab l e i n f o r m a t i o n f ac t in an ap p l i-c a t i o n en v i r o n m en t co r r e s p o n d s t o an o b j ec t i n a3 D I S d a t a b a s e . S i m p l e , c o m p o u n d , a n d b e -h av i o u r a l en t i t i e s i n an ap p l i c a t i o n en v i r o n m en t ,a t t r i b u t e s o f o b j ec t s an d r e l a t i o n s h i p s a m o n g o b -jec t s , as wel l as ob jec t g roupings and c las s i f i ca-t i o n s a r e a l l m o d e l l ed a s o b j ec t s . W h a t d i s t i n -g u i s h e s d i f f e r en t k i n d o f o b j ec t s in a 3 D I Sd a t ab as e i s t h e s e t o f st r u c t u r a l an d n o n s t r u c t u r a l( d a t a ) r e l a t i o n s h i p s d e f i n ed o n t h em .

T h e c o n c e p t w h i c h w e h a v e e x p l o it e d t o m o d e lm u l t i p l e lev e l s o f ab s t r ac t i o n is i n s t a n t i a t i o n /c l a s si f ic a t io n . H o w ev e r t h e s em an t i c s o f t h e s et e r m s a r e n o t d e f i n ed i n R e f . [1 ] . O u r i n t e r p r e t a -t ion i s tha t an ins tance of a c l as s i s an ob jec tw h o s e t y p e i s t h e c l a s s an d w h i ch h a s v a l u e s f o rt h e a t t r i b u t e s o f t h a t c l a ss . F o r ex am p l e , E n g i n e1.8 l i tre, with turbo) i s an i n s t an ce o f t h e o b j ec ten g i n e d e f i n ed a s Eng ine H A S s ize 1 .8 l it re O R2 .0 l it re ) A N D turbo wi th O R wi thou t ) ) .

E l . 8 , I s - a -m e m b e r - o f , { E n g i n e } )E l . 8 , H a s - f u e l - e c o n o m y , { 1 6 k m / l i t r e } )E l . 8 , H a s - g e a r b o x - i n t e r f a c e , { G 1 . 8 } )E l . 8 , H a s - v a r i a n t - s t a r t - d a t e , { 1 9 9 3 - 3 } )E l . 8, H a s - c o m m e r c i a l - p a r a m e t e r s , { E n g i n e - s i z e = l . 8 , T u r b o = n o } )

F i g . 8. E n g i n e i n s t a n c e l e v e l E l .8 o n l y ) .


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4 F. Erens et aL / Computers in Industry 24 1994) 17-28O f c o u r s e t h i s i n t e r p r e t a t i o n c o u l d b e i n c o r -

r e c t . A n o t h e r p r o b l e m w i t h 3 D I S i s t h a t i t a p -p e a r s t o b e w e a k l y t y p e d ; i t i s n o t c l e a r h o w ( o re v e n i f) t h e c o n f o r m a n c e o f i n s t a n c e s t o t h e i rt y p e s i s g u a r a n t e e d . I n p r a c t i c e t h e c o n f o r m a n c eo f i n s t a n c e s t o t h e i r t y p e s i s e ss e n t ia l . F o r e x a m -p l e , it m u s t n o t b e p o s s i b l e t o d e f i n e a n e n g i n ew i t h o u t g i v in g e x a c tl y t w o v a l u e s o f t h e c o r r e c tt y p e s: o t h e r w i s e t h e e n g i n e d e f i n i t i o n w o u l d b ei n c o m p l e t e o r i n c o r r e c t i n s o m e o t h e r w a y .

F i n al ly , 3 D I S d o e s n o t a p p e a r t o s u p p o r t m o d -u l a r i z a t io n . T h e e f f e c t o f t h is i s t h a t t h e d a t as t r u c t u r e s w h i c h n e e d t o b e p o p u l a t e d d u r i n gd i f f e r e n t d e s i g n a c t iv i t ie s a r e m i x e d w i t h i n s t a n c ed a t a a n d a r e t h e r e f o r e n o t r e a d i l y v i si b le . U n d e r -s t a n d a b il i ty i s a n i m p o r t a n t r e q u i r e m e n t o f d a t am o d e l s [ 9] a n d a 3 D I S d a t a b a s e o f a r e a l e n g i-n e e r i n g e x a m p l e w o u l d b e u n l i k e ly t o s u p p o r t t h isr e q u i r e m e n t .

S o , w h i ls t 3 D I S s u p p o r t s t h e i m p l e m e n t a t i o no f m u l t i p l e l e v e l s o f a b s t r a c t io n , a b e t t e r w a y o fd e s c r i b i n g t h e d a t a a n d i t s s t r u c t u r e i s r e q u i r e d .T h e L e e d s S t r u c t u r e E d i t o r , d e s c r i b e d i n t h e n e x ts e c t i o n , p r o v i d e s s u c h a c a p a b i l i t y . O n c e t h es t r u c t u r e a n d c o n t e n t o f th e d a t a h a v e b e e n d e -t e r m i n e d u s i n g s u c h a to o l i t c o u l d b e i m p l e -m e n t e d , w i t h t h e a p p r o p r i a t e u s e r i n t e r f a c e a n dt y p e c h e c k i n g t o o l s , i n a d a t a b a s e s y s t e m s u c h a s3 D I S .

5. Applying the Leeds Structure Editor for product fami ly model l ing5 1 An introduction to the Leeds Structure Editor

g e o m e t r i c e v a lu a t o rs , v e c t o r p a c k a g e s a n d c u t t e rp a t h g e n e r a t i o n p r o g r a m m e s .

S E ' s d a t a d i c t io n a r y h a s a n u m b e r o f c o n -s t r u c t s w h i c h a l l o w e n g i n e e r s t o c r e a t e d i r e c t e dg r a p h s , c o n s i s t in g o f n o d e s a n d r e l a ti o n s . T h e s ea r e :- c o l l e c t i o n s ( C O L ) o f o t h e r n o d e s (g r o u p ) ;- s e l e c t io n s ( S E L ) o f o t h e r n o d e s (c h o i c e );- l is t s o f n o d e s , w h i c h a r e a ll o f t h e s a m e t y p e ;- a t o m s , w h i c h a r e l e a v e s i n t h e h i e r a r c h i c a l

s t r u c t u r e , t h e b a s i c t y p e s o f t h e S E .T h e h i e r a r c h i c a l s t r u c t u r e t h a t i s c r e a t e d w i t ht h e s e c o n s t r u c t s i s c a l l e d t h e m e t a - s t r u c t u r e ,c o m p a r a b l e w i t h a s c h e m a i n a d a t a b a s e ( le v e l 2i n F i g . 4 ). T h e d a t a d i c t i o n a r y ( l e v e l 1 i n F i g . 4 ) isc a l l e d t h e b o o t s t r a p m e t a - s t r u c t u r e a n d i s h a r d -w i r e d i n t h e S E . A l l m e t a - s t r u c t u r e s c a n b e r e -g a r d e d a s i n s t a n c e s o f t h is b o o t s t r a p m e t a - s t r u c -t u r e . T h e m e t a - s t r u c t u r e s c a n b e p o p u l a t e d ( i n -s t a n t i a t e d ) w i t h v a l u e s i n a s i m i l a r w a y a s i nd a t a b a s e s . F i g . 9 s h o w s h o w t h e c a r s t r u c t u r e o fF i g . 3 ( c o m p l e t e d w i t h v a r i a n t s ) c o u l d b e m o d -e l l e d in t h e S E . H e r e , t h e c a r f a m i l y is m o d e l l e da s a m e t a - s t r u c t u r e , w h i l e t h e v a r i a n t s a r e m o d -e l l e d a s i n s t a n c e s o f t h i s m e t a - s t r u c t u r e .

T h e a b o v e m e t a - s t r u c t u r e h a s t h e m a i n d i s ad -v a n t a g e t h a t i t c a n o n l y b e u s e d f o r m o d e l l i n gv a r i a n t s o f t h e c a r p r o d u c t f a m i l y . I t is n o t g e n e r i ce n o u g h f o r m o d e l l i n g c o m p l e t e l y d i f f e r e n t f a m i -l i e s , e . g . a e r o p l a n e s a n d m e d i c a l e q u i p m e n t . T h i sd e f i c i e n c y c a n , h o w e v e r , b e o v e r c o m e b y a c h a r -a c t er is t ic o f t h e S E , n a m e l y a n i m p l e m e n t a t i o n o fA - c a lc u l u s w i t h w h i c h m u l t i p l e a b s t r a c t i o n le v -e l s c a n b e c a p t u r e d .

T h e L e e d s S t r u c t u r e E d i t o r ( S E ) is a t o o l t h a th a s b e e n d e v e l o p e d t o c r e a t e a n d e d i t p r o d u c td a t a s t r u c t u re s . O n e o f th e p r o b l e m s o f to d a y ' sc o m p u t e r s y s te m s is t h a t p e o p l e m u s t r e s t r u c t u r et h e c o n t e n t s o f t h e i r m i n d s s o t h a t s o f t w a r e a p p l i -c a t i o n s c a n u s e t h e i n f o r m a t i o n h e l d t h e r e . T h eS E h a s b e e n c o n c e i v e d w i t h th e i d e a t h a t p e o p l e ,p a r t i c u l a r l y e n g i n e e r s , c a n i n t e r a c t w i t h t h e c o m -p u t e r i n a w a y w h i c h g i ve s t h e m c o n t a c t w i t ht h e i r s t r u c t u r e d d a t a [1 0]. S e v e r a l p i e c e s o f so f t-w a r e h a v e b e e n w r i t t e n t h a t m a k e u s e o f d a t af r o m t h e L e e d s P r o d u c t D a t a E d i t o r , i n c l u d i n g

car

ch ass i s i n te r io r en g i n e g ear b o xd ash ~

5 vadant s e a t b o a r dF ~ ~ 1 4 variants 3 vadantsb b2 variants 2 variants

Fig. 9. Car m odel led in the Leed s Structure Editor.


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26 F. Erens et aL / Computers in Industry 24 1994) 17-28T h e I F - T H E N s t a te m e n t s in th e b o d y o f t h ef u n c t i o n a r e u s e d t o d e t e r m i n e t h e r i g h t p r i m a r yv a r i a n t o f th e e n g i n e . O n e o f th e s e v a r i a n t s w il lb e r e t u r n e d b y th e f u n c t i o n , w h e n t h e f u n c t i o n isi n v o k e d w i t h p a r a m e t e r v a lu e s .

W e n o w c a n r e p l a c e a s p e c i f ic v a r i a n t o f t h ee n g i n e b y t h e f u n c t i o n E n g i n e :c o d e = E 1 . 8 ti s r e p l a c e d b yc o d e = E n g i n e e n g i n e s iz e = [ 1 .8 , 2 . 0] ,

t u r b o = [ y e s , n o ] )W h e n w e g i v e v a l u e s to t h e p a r a m e t e r s o f th i sf u n c t i o n a n d e v a l u a t e t h e f u n c t io n , t h e n t h e f u n c -t i o n s t r u c t u r e i s r e m o v e d a n d t h e p r e v i o u s v a l u eo f t h e c o d e o f t h e e n g i n e i s r e p l a c e d b y t h e r e s u l to f t h e f u n c t i o n E n g i n e :c o d e = E n g i n e e n g i n e s iz e = 2 .0 ,

t u r b o = n o )i s e v a l u a t e d a n d r e s u l t s i nc o d e = E 2 . 0w h i c h i s a n i n s t a n c e o f t h e m e t a - s t r u c t u r e o f F i g .10 a ga in .

T h i s a p p r o a c h m i g h t l o o k r a t h e r c o m p l e x , b u th a s p r o v e d t o b e s a t i s f a c t o r y f o r m o d e l l i n g ap r o d u c t f am i ly . T h e e f f o r t o f p a r a m e t r i z i n g v a ri -a n t s t o c r e a t e f a m i l i e s i s s m a l l . F u r t h e r , t h e d i f -

f e r e n t m o d e l s o n d i f f e r e n t a b s t r a c t i o n l e v el s ) a r es m a l l a n d e a s y t o se e . T h e A - f u n c ti o n s w h i c h a r eu s e d f o r m o d e l l i n g c o m p o n e n t f a m i l i e s c a n e a s i l yb e s h a r e d b y d i f fe r e n t p a r e n t f a m i l ie s , th e r e b ye l i m i n a t i n g d a t a r e d u n d a n c y a n d s t i m u l a t i n g r e -u s e .5.3. Sum mary of approaches

T a b l e 5 g i v e s a n o v e r v i e w o f t h e r e l a t i o n a l ,o b j e c t - o r ie n t e d , 3 D I S a n d L e e d s S t r u c t u r e E d i t o ra p p r o a c h e s .

F r o m t h e t a b l e i t c a n b e s e e n t h a t b o t h t h er e l a ti o n a l a n d t h e o b j e c t - o r i e n t e d a p p r o a c h e s c a no f f e r t h r e e l e v e l s o f a b s t r a c t i o n t o m o d e l f o u rl e v e ls o f a b s t r a c t i o n ; t h u s t w o t h r e e - l a y e r m o d e l sa r e n e e d e d t o m o d e l f o u r l ev e ls , w h i c h r e s u l t s i nd u p l i c a t i o n i n d i c a t e d b y it a li c s) . P r o d u c t f a m i li e sl e v e l 3 ) a r e i n s t a n c e s o f p r o j e c t m a n a g e m e n tl e v e l 2 ) a n d a r e r e p e a t e d a s t a b l e s o r c l a s s e sl e v e l 2 ) o f t h e p r o d u c t v a r i a n t s l e v e l 3 ) . T h i s

r e s u l t s i n a r e l a t i o n s h i p f r o m p r o d u c t f a m i l i e s a si n s t a n c e s t o p r o d u c t f a m i l i e s a s c l a s s e s , w h i c h i sd i f f i c u l t t o e x p r e s s i n r e l a t i o n a l a n d o b j e c t - o r i -e n t e d d a t a b as e s . T h e b e n e f i t o f o b j e c t - o r i e n t e dd a t a b a s e s o v e r r e l a t io n a l d a t a b a s e s is t h e p o s s i -b i l i t y t o i n h e r i t s t r u c t u r a l i n f o r m a t i o n , w h i c h r e -d u c e s t h e r e d u n d a n c y o f i n f o r m a t i o n o n a n a b -s t r a c t i o n l e v e l .

B o t h t h e 3 D I S a n d t h e S E a p p r o a c h e s s u p p o r tt h e d i r e c t m o d e l l i n g o f m u l t i p l e l e v el s o f a b s t r a c -t i o n . T h e S E i s g e a r e d t o w a r d s a l l o w i n g p e o p l e t os e e a n d i n t e r a c t w i t h t h e s t r u c t u r e a n d c o n t e n t o ft h e i r d a t a a n d a g e n e r a l - p u r p o s e g r a p h i c a l u s e r

Table 5Summ ary of app roachesL ev e l Re latio na l Object-oriented 3DIS Leeds SE1 Data Meta-class Object Bo otstrap meta-structu redictionary2 Project Product P r o j e c t Product P r o j e c t M e t a - s t r u c t u r eor variantsm a n a g e m e n t f a m i l i e s m a n a g e m e n t f a m i l i e s m a n a g e m e n t3 Product Product Product Product P ro d u ct Product families A-calculus)families va r i a n t s families va r i a n t s f a m i l i e s4 Product Product variantsvariants


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F. Erens et al. / Computers in Industry 24 (1994) 17 -2 8 27

i n t e r f ace s u p p o r t s th i s i n t e r ac ti o n . 3 D I S o n th eo t h e r h an d is a d a t ab as e s y s t em w h i ch is b e s tu s ed i n co n j u n c t i o n w i t h s o p h i s t i c a ted an d p o s s i -b l y d a t a s t r u c t u r e s p ec if ic u s e r an d ap p l i c a t io ni n t e rf ace s . I n p r ac t i c e b o t h s y s t em s h av e a r o l e t op l ay : t h e S E a l l o w s p eo p l e t o p r o t o t y p e an d t e s tt h e i r d a t a s t r u c t u r e s w h e r ea s 3 D I S p r o v i d e s ad a t a b a s e e n v i r o n m e n t i n w h i c h t h e t e s t e d d a t as t r u c t u r e s c a n b e i m p l e m e n t e d a n d u s e d i n ap r o d u c t i o n en v i r o n m en t .

6 C o n c l u s i o n sT h i s p ap e r h a s t r i ed t o r a i se an a w ar en e s s w i th

r e s p ec t t o ab s t r ac t i o n l ev e l s . T h e d ev e l o p m en t o fp r o d u c t s an d p r o d u c t f am i l ie s i n p a r t i cu la rs h o w s t h a t t h e r e a r e m o d e l l i n g p r o b l e m s w h i c hcan n o t b e s o l v ed d i r ec t l y i n r e l a t i o n a l o r o b j ec t -o r i en t ed d a t ab as e s . F o r c i n g m u l t i p l e ab s t r ac t i o nl ev e l s i n t h r ee d a t ab as e l ev e l s i n t r o d u ces m o r ec o m p l e x s c h e m a w i t h i n h e r e n t r e d u n d a n c y . A l -t h o u g h t h i s p r o b l em i s g en e r a l l y k n o w n w i t h ex -p e r i e n c e d d a t a b a s e d e s i g n e rs n o t m u c h a t t e n t io nh as b een p a i d t o t h i s s u b j ec t i n l i t e r a t u r e o rs o f t w a r e d e s ig n . T w o acad em i c ap p r o ach e s t h e3 D I S a n d th e L e e d s P r o d u c t D a t a E d i t o r h a v eb ee n d ev e l o p ed to ta ck l e m u l t i p le ab s t r ac t i o nl ev e l s . T h ey ap p ea r t o b e ap p r o p r i a t e f o r m o d -e l li n g p r o d u c t f am i li e s b u t s u p p o r t ed s o f t w a r e o fth i s k ind i s no t ye t ava i l ab le .

AcknowledgementT h i s w o r k h a s b e e n p a r tl y f u n d e d b y t h eA C M E D i r e c to r at e o f S E R C G r a nt N o . G R / H

24266.

References[1 ] H . A f s a r m a ne s h a nd D . Mc L e od , Th e 3D I S : A n e x t e n -

s i b l e ob j e c t - o r i e n t e d i n f o r m a t i on m a na ge m e n t e nv i r on -m e n t , A C M Trans . In f. Sys t. , Vol . 7 , No. 4 , October1989, pp. 339-377.

[ 2 ] E .A . va n V e e n , Modelling Product Structures by GenericBills-of-Materials, El s e v i e r , A m s t e r da m , 1992 .

[3] STEP Par t 44, ISO-10303-44, Product Data Representation a nd Exc ha nge , I n t e g r a t e d G e ne r i c R e s ou r c e s : P r od -uc t S t r uc t u r e C onf i gu r a t i on , D r a f t I n t e r na t i ona l S t a n -dard , 1993.[ 4] P . G u , PM L: P r oduc t m ode l l i ng l a ngua ge , Computersin Industry, Vol . 18, 1992, pp. 265-277.[ 5] F . J . E r e ns , H .M .H . H e gge , E .A . va n V e e n a nd J .C .Wo r t m a nn , G e ne r a t i v e b i l ls - o f - m a t er i a l: A n ove r v i e w ,Proc. IF1P 92, El s e v i e r , A m s t e r da m , 1992.[ 6] J . J , va n G r i e thuys e n , C on c e p t s a nd t e r m i no l ogy f o r t hec o n c e p tu a l s c h e m a a n d t h e i n f o rm a t i o n b a s e , I S O /TC 97 / SC 5 N 695 , 1982 .17] W. Kim (Ed. ) , Object-Oriented Concepts, Databases andApplications, A C M Pr e s s , 1989 .[8] J .R . Abr ia l , D ata sema nt ics , in J .W. Kl imbie and K.L.K of f e m a n ( Eds .) , Data Management Systems, N o r t h - H o l -l a nd , A m s t e r da m , 1974 .[9] C . Bat in i , M. Lenze r in i and S.B . Nav athe , A com para-t ive analys i s of methodologies for da tabase schema in te-g r a t i on , ACM Comput . Surv . , V ol . 18 , N o . 4 , D e c e m be r1986, pp. 323-364.[ 10 ] A . Mc K a y , Th e S t r uc t u r e Ed i t o r a pp r oa c h t o p r oduc tde s c r i p t i on , U n i ve r s i t y o f Le e ds , I SS P r o j e c t R e s e a r c hR e por t , I SS- PD S- R e por t - 4 , J une 1988 .

F r e de r i k Er e ns ga i ne d h i s de g r e e i nI n f o r m a t i on Sc i e nc e i n 1990 , a f t e rw h i c h he be c a m e a c ons u l t a n t a tK PMG Li gh t hous e . S i m u l t a ne ous l y ,he s t a r t e d a s a R e s e a r c h Eng i ne e r i nt he D e pa r t m e n t o f I ndus t r i a l Eng i -ne e r i ng a nd Ma na ge m e n t Sc i e nc e s ,E i ndhove n U n i ve r s i t y o f Te c hno l ogy .H i s c u r r e n t r e s e a r c h i n t e r e s t s i nc l udeproduct model l ing, in tegra l logi s t i csa n d t h e d e v e l o p m e n t o f c o m p le x

products which are of tered in a l a rge var ie ty .A l i s on Mc K a y ga i ne d he r de g r e e i nM e c h a n i c a l E n g i n e e r i n g i n 1 9 8 2 a n dt he n s pe n t t w o ye a r s i n i ndus t r y be -f o r e b e c o m i n g a R e s e a r c h E n g i n e e ri n t h e D e p a r t m e n t o f M e c h a n i c a l E n -g i ne e r i ng . H e r r e s e a r c h i n t e r e s t s i n -c l ude t he r e p r e s e n t a t i on a nd i n t e g r a -t i on o f p r oduc t da t a . S i nc e 1988 s heha s t a ke n a n a c t i ve r o l e i n STEP,par t i cular ly in in tegra t ion, develop-m e n t m e t hods a nd a s a e d i t o r o f Pa r t

41 . C ur r e n t l y s he i s l e a d i ng t he p r oduc t da t a m ode l l i ng a ndi n te g r a ti o n a ct iv i ti e s o f t h e S E R C / A C M E - f u n d e d M O S E S( Mode l O r i e n t e d S i m u l t a ne ous Eng i ne e r i ng Sys t e m s ) p r o j e c t .


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F. Erens et al. / Computers in Industry 24 1994) 17-28Susan Bloor gained her degree inMathematics in 1962 and her PhD in1965. She is Senior ComputationalAdvisor in the Department of Me-chanical Engineering. Her researchinterest is in engineering product datamodelling and its role in systems inte-gration. She has played a leading rolein the Departm ent s resea rch activi-ties in this field for many yearsthrough a continued involvement in

t Ma nager for various European-fun ded projects.

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