Functional modeling for enabling adaptive design of devices for new environments

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<ul><li><p>Functional modeling for enabling adaptivedesign of devices for new environments</p><p>Sattiraju Prabhakara ,* &amp; Ashok K. GoelbaSchool of Computing Sciences, University of Technology, PO Box 123, Broadway, Sydney, NSW 2007, Australia</p><p>bCollege of Computing, Georgia Institute of Technology, Atlanta, GA 30332, USA</p><p>Current AI research on adaptive design is limited to devices with minimal interactionswith their environments. This is partly because current functional models are limitedto devices with minimal environmental interactions. We describe a functionalrepresentation scheme, called the Environmentally-bound StructureBehaviorFunction (or ESBF) model, to represent and organize knowledge of the functioningof a device, including the role of its environmental interactions. We also describe aprocessing strategy called Environmentally-driven Adaptive Modeling (or EAM) formodifying a known design for operation in a new environment, and thus for carryingout new functions that arise due to new deviceenvironment interactions. Weillustrate the ESBF and EAM through the example of adapting the conceptual designof a refrigerator to obtain a preliminary design of an air-conditioner. We also discussthe implementation of this example in a computer program called EnvironmentalKRITIK. q 1998 Elsevier Science Limited. All rights reserved.</p><p>Key words: functional modeling, design, adaptation, reuse of experiences, environ-mental interactions.</p><p>1 DEVICES AND THEIR ENVIRONMENTS</p><p>Much AI research on device design has focussed on deviceswhose functioning can be modeled with minimalrepresentation of environmental interactions. Consider, forexample, classical AI design systems such as R1,1AIR-CYL,2 PRIDE,3 VEXED4 and VT.5 Typically, thesesystems use heuristic search for a new device design,accommodating interactions among the components of thedevice but largely ignoring the interactions of the devicewith its environment. In this paper, we present an approachfor designing devices that makes use of functional models ofdevices which incorporate, into the model, the interactionsbetween the device and its environment.</p><p>1.1 Functional modeling for design</p><p>A design task can be defined as transforming the require-ments of an artefact to a physical product description of thatartefact that satisfies the requirements. The designedproducts can also be represented using qualitative modelswith the structure and behavior of the artefact. Physicaldescriptions and qualitative behavioral descriptions cannot</p><p>address the tasks required to be performed during theprocess of designing the artefact.</p><p>(1) Verification and prediction: once the design task iscomplete, it should be possible to verify the artefactdescription to see whether it satisfies the require-ments or not. It is also required to test, at variousstages of the design process, that the artefactdescription addresses the requirements.</p><p>(2) Incorporating designers rationale: the artefactdescriptions need to provide explanations as tohow the devices work. This will enable one to testwhether the artefact will work or not.</p><p>(3) Addressing the synthetic task: design requiressynthesizing component-related descriptions into anartefact description. This is in addition to analyticaltasks such as simulation of the artefact behavior.</p><p>The functional modeling approach suggests that anartefact is modeled in terms of function, i.e. what it isintended to do, and how the intentions are to beaccomplished through causal interactions among com-ponents of the device.6 Here, the requirements are specifiedas functions of the artefact. Geros7 method for designingartefacts, using functional modeling, suggests that thestructure of the artefact is not directly generated fromthe requirements. In this model of design synthesis, the</p><p>Artificial Intelligence in Engineering 12 (1998) 417444q 1998 Elsevier Science Limited</p><p>All rights reserved. Printed in Great Britain0954-1810/98/$19.00PII: S 0 9 5 4 - 1 8 1 0 ( 9 8 ) 0 0 0 0 3 - X</p><p>417</p><p>*Author to whom correspondence should be addressed.E-mail:</p></li><li><p>expected behavior of causal interactions is generated fromthe function. The expected behavior is transformed to a struc-ture. From the structure, the physical behavior of the artefactis derived. The expected behaviors are compared to the actualbehaviors of the structure of the physical artefact. Theexpected behavior is reformulated based on the comparison.7</p><p>The functional modeling work in design has attempted toaddress a variety of design tasks using different kinds offunctional models. These models can be summarized ashaving the following features:8,9</p><p>(1) Representational grounding: the functions canbroadly differ based on whether they are theintentions on structure or behavior. The behaviorsof an artefact are abstracted to satisfy a designintent. Here, the functions are grounded in theabstracted behaviors.6,10 An example of groundingfunctions over structure is a display function withthe intent of displaying some aspects of structureof the artefact.11</p><p>(2) Levels of intention: the functions vary in the level ofabstraction of function in terms of its meaning.</p><p>(3) Functional decomposition: a function of an artefactis decomposed into subfunctions, where each sub-function is mapped onto different aspects of theartefacts.</p><p>(4) Relating function with other kinds of knowledge:qualitative behavioral models have used generalfirst principles knowledge to generate behavioralmodels. Functional models represent the specificroles of the first principles in generating behaviorsegments in order to achieve a functionality.6,10</p><p>(5) Representing function in context: functionalrepresentations that explicitly embed an artefactinto its environment.12</p><p>1.2 Functional modeling for adaptive design</p><p>An alternative method to routine design used in designresearch is adaptive design, in which old design cases areadapted to address new design problems.13,14 For adaptingpast design cases to design new devices, qualitative modelsof devices are used to represent design cases.1518 Thesequalitative models represent relationships between structureand behavior of devices, with minimal representation ofenvironments.</p><p>In addition, functional modeling of devices has allowedformalization of the design task and the process of adaptivedesign.13 A design task can be defined as mapping from afunction of the device or the goals of the designer for thedevice to the structure of the device. Each design case isrepresented as a mapping from the structure of the device tothe function of the device. The design of a new device, i.e.achieving a new functionality, is done by adapting astructure to function mapping of a known device to achievethe new functionality. The functional models are used torepresent design cases, from which adaptation spaces aregenerated for solving a new design problem. The adaptation</p><p>spaces for designing new devices can be generated provideda functional model has the following properties.</p><p> Localization of functional aspects of the deviceonto structural aspects of a design case. Thislocalizability property is not inherent in allmodels, e.g., models of non-linear functions.</p><p> Isolable modification of a localized element of apast design case. The modification of local elementsshould preserve the remaining models of the designcase, primarily the localizability property of the restof the model. This enables the model to preserve theremaining functional aspects and their adaptability.A further consequence of this property is that theadapted model itself is adaptable, thus ensuring apotentially infinite sequence of adaptable models.Therefore, the adaptation spaces generated containmodels that are functional variations of the pastdesign.</p><p>The Structure, Behavior and Function (SBF) model10has the above properties. KRITIK10,16 and IDEAL19,20demonstrate the usefulness of these properties in a numberof systems for various domains.</p><p>The following aspects of the SBF models enablelocalization and isolable modification properties to besatisfied.</p><p>(1) Functional closure of behavior: in SBF models, onlyfunctionally relevant behaviors are represented. Thisallows functions to be directly mapped onto behaviors,and no other behaviors are present in the functionalmodel that does not have functional significance.</p><p>(2) Causal closure over structure: each of the behavioralstates in an SBF model is closed over a device sub-structure and includes a small set of structuralelements of the device. A causal event links twosuch states by a behavioral state transition. Thisaspect of an SBF model suggests that if there is afunctionally relevant event, then it can be mappedonto a small group of structural elements.</p><p>(3) Equivalence of events across functions: two eventsare equivalent if their behavioral states andbehavioral state transitions are equivalent. Thestates, or the state transitions, are equivalent iftheir elements are equivalent. Both of these arerepresented using a global ontology that ensurestheir equivalence. This point enables modifiabilitywithout disturbing the equivalence structure in therest of the model.</p><p>(4) Localizable causes: a state is a causal result ofanother state that lies in a sequence of state transi-tions within the same behavior. This makes use ofthe transitive nature of the causal relationshipsbetween states. This closedness makes the searchfor a behavioral state transition localizable.</p><p>Many functional models possess one or two of the aboveproperties,2123 but not all. SBF models provide a powerfulsolution for adaptation problems.</p><p>418 S. Prabhakar, A. K. Goel</p></li><li><p>However, this functional modeling of devices allows onlya minimal modeling of the environment:</p><p>(1) Minimal role of the environment: the device isassumed to have a small set of input and outputstates compared to its large number of internalbehavioral states. Changes in behavioral states ofenvironment often do not contribute to thefunctionality of the device.</p><p>(2) Passive role of the environment: changes in thestates of the environment are brought about by thedevice, but the environment plays no distinct role inthe functioning of the device.</p><p>For these reasons, SBF models are limited in designingdevices for new environments. Furthermore, they face thefollowing problems while addressing the design for newenvironments by adapting past experiences.</p><p>(1) Incomplete model generation: since the environmentof a device is not explicitly modeled, the adaptationof SBF models generates incomplete modelsamodel of the device that does not capture the aspectsof its environment.</p><p>(2) Non-adaptable adaptations: multiple SBF modelsdescribing different designs may be composed toarrive at an SBF model of the new device.16 Sinceeach SBF model represents environmental inter-actions, however minimally, the resulting SBFmodel would also minimally represent the environ-mental interaction. Since the environmental inter-actions are not explicitly modeled in an SBFmodel, this combination of SBF models in anadaptation can give rise to unpredictable results.That is, it is not possible to conclude which environ-mental aspects the adapted SBF model wouldincorporate.</p><p>(3) Large adaptation spaces: since an adaptation doesnot consider the environments, it is underconstrainedfor the requirements of the environments. The result-ing adaptation space may be very large orinappropriate for an environment.</p><p>The following issues become important in modelingenvironments for adaptation.</p><p>(1) Easy replaceability of environments: devices arephysically moved from one environment to another,but can still deliver their functions. The functionalmodel of the device needs to meet this criterion.Since a designer may not be aware of all environ-ments in which a device can be operated or theremay be no generic model of all environments, thedevice models will often be incomplete. The onlysolution is to change the model of the environment.This change in environmental model may suggestsome changes in device model, but together theystill need to support a consistent behavior.</p><p>(2) Supporting close, yet acausal, interactions betweendevice and environment: an environment is not a part</p><p>of a device in the same sense that a component of adevice is a part. This is because the environmentdoes not causally contribute to the functionality ofthe device. An environment often provides aphysical situation in which the causal events of thedevice take place. Devices and their environmentschange dynamically and their event structuresdepend upon each other. The functional modelshould be able to capture this dependency.</p><p>(3) Modeling environments without intrinsic functions:in contrast to devices which are designed for specificfunctions, environments are often not designed tosatisfy any functions. For example, the environmentof an automatic coffee-maker can be a room which isnot specifically designed to support the function ofcoffee-making. Devices are said to have intrinsicfunctions, whereas environments give rise toascribed functions. The inherent process of thedevice supports the intrinsic functions. On theother hand, the ascribed functions are achieved byascribing a structure to the environment that cansupport the function.</p><p>In order to address the above issues, we have developed anew functional representation scheme that extends the SBFmodel to represent deviceenvironment interactions andtheir role in the functioning of the device. We call the newscheme the Environmentally-bound StructureBehaviorFunction (ESBF) model. In contrast to SBF models andother functional representation schemes, the ESBF modelviews a device function not as an abstraction of the internalbehaviors of the device, but as an abstraction of the inter-actions of the device with its external environment. ESBFgives rise to a new processing strategy, called Environmen-tally-driven Adaptive Modeling (EAM), for adapting thedesign of a known design for operation in a new environ-ment and for carrying out new functions based on the newenvironmental interactions. Unlike the adaptive modelingstrategy used in the KRITIK system, EAM explicitly takesinto account deviceenvironmental interactions.</p><p>ESBF and EAM arise from a detailed analysis of threehistorical case studies of technological invention: theautomatic coffee-maker,24,25 the room air-conditioner26,27and the windmill.28 In this paper, we illustrate the ESBFmodel and the EAM strategy through the example ofevolution of the preliminary design of the air-conditionerfrom the conceptual design of the refrigerator.29,30 Thediscussion focusses on the adaptation task as opposed toother tasks of adaptive design, such as design retrieval,design verification, redesign and design storage.</p><p>A computer program called Environmental KRITIK(E-KRITIK) implements and evaluates the EAMstrategy for the task of adapting an ESBF of therefrigerator into an ESBF model of the air-conditioner.In this paper, we briefly describe E-KRITIK. Wealso discuss its limitations and how it might beextended for addressing some of the...</p></li></ul>