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M. Fredj – Ingénierie des modèles0

Le cycle de vie des modèles (1) Model construction is not instantaneous. Let us take an example to

illustrate this.

Suppose you are arriving for the first time in a given ton! forexample Seattle! "a.! to attend a conference. #he donton hotelhere you are staying gives you some indications on ho to go tothe conference! here to go shopping or dining out in the evening!etc.

 $ll the actions that you ill undertake like going to visit a museummay %e carried out successfully and expediently if preceded %y aplanning phase here a model ill %e %uilt (map of donton).

&n the a%sence of such a model or ith a too imprecise or evenrong model! the alk to a particular place may take a very longtime.

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M. Fredj – Ingénierie des modèles1

Le cycle de vie des modèles (') $s your stay in Seattle goes on! your model of thearea %ecome more and more precise and your travelsto interesting spots take less time.

 our knoledge of the ton is %eing progressivelyenriched and updated. #he corresponding mentalmodel you have %uilt is composed of   entities (theonvention enter! the *inancial +istrict! the Spaceenter! your ,otel! the $rt Museum! -ine Street! 1st

 $venue! etc.).

&t is also composed of facts that you are constantlyadding! assessing and using like the o%servation thatrd $venue is parallel to 1st $venue and perpendicularto -ine street! that -ine street lead to -ike -laceMarket and that your hotel is near the intersection of -ine street and /th $venue.

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M. Fredj – Ingénierie des modèles'

Le cycle de vie des modèles () $t some time you may %uy a dontonalkingmap. #his is a model of previous experience %y otherpeople and you are %uying this experience to validateand to enrich your on knoledge.

 $s you continue to visit the ton! you may get a mapof the pu%lic transportation (%uses! monorail andunderground). #his data ill also contri%ute to enrichyou operational knoledge.

"hat is interesting is that you ill eave the

information contained in different maps (alking mapand pu%lic transportation map) %y connecting  ointpoints in the different models.

2f course this is made possi%le %ecause the different maps are models of the samesystem (the city of Seattle). $t some time you may even use a %ike and findconvenient to use a speciali3ed map indicating recommended routes.

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M. Fredj – Ingénierie des modèles

Le cycle de vie des modèles (4)

&n the left %ottom part of the %ike route map!there is a rectangle area providing the 5legend5.

#his is hat e6ll call later a metamodel sinceit defines the meaning of the various iconsappearing in the model (the map). &t6s the keyto interpreting the map as a description of thereal territory.

 $nsering a 7uestion a%out the time it ill take

to alk or %ike from the Space 8eedle to -ike-lace Market re7uires the legend informationthat four centimeters on the map correspondsto 900 meters on the ground. $pplying ashortest path algorithm to the map is then easyand ill lead to the re7uested anser.

:uilding a company %usiness information system is a

progressive operation! similar to %uilding a personal map of Seattle.

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M. Fredj – Ingénierie des modèles4

Le cycle de vie des modèles ; r<sum<

#he example maps taken in the previous section may help us illustratingsome key points on modeling. Let us summari3e and generali3e here someo%servations ust made that could apply to general models as ell as to

maps. #he first idea is that a map is a graphical model of a given territory. =raphics

artifacts may ease cognitive tasks %y using elements and spatial relationsamong them to re present a%stract or concrete facts a%out a specific portion of the real or imagined orld.

 $nother idea is that here are several kinds of maps (alking! pu%lictransportation! road map! etc.). >ach map has a specific intended usage and is%uild for some specific purpose.

#he (graphical) language of a map is defined %y a legend! hich is attached tothe map (loosing the legend may render the map 7uite useless). #he legend is

itself ritten in a graphical language that is left implicit (lines and %oxesmainly).

 $nother finding is that maps may %e progressively ela%orated. $t some time amap may %e rong (hristopher olum%us used rong maps that he helped tocorrect). Maps may %e considered as assets that may help to transfer expertise

%eteen different people and different contexts.

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M. Fredj – Ingénierie des modèles9

?sually original models like maps may not %e ela%oratedautomatically! %ut automatic means may help to %uild them. $n

aerial photograph does not make a good map! %ut it may help toela%orate it.

2ne common idea is that more a map is precise! more useful itis. #his may %ear some truth %ut should %e taken ith caution.

#he riter @orge Luis :orges records the folloing story. #ocompeting teams of geographer ere competing in %uildingmore and more accurate maps of a given country. $t one timeone of the team on %y providing maps ith the exactdimension of the territory! on a scale of one to one. $t the exact

time these maps achieved maximum precision they also lost anypractical utility.

 $ map represents a given territory %ut a map is different fromthe territory. &t is a model of a system.

Le cycle de vie des modèles ; r<sum<