Functional modeling for enabling adaptivedesign of devices for new environments
Sattiraju Prabhakara ,* & Ashok K. GoelbaSchool of Computing Sciences, University of Technology, PO Box 123, Broadway, Sydney, NSW 2007, Australia
bCollege of Computing, Georgia Institute of Technology, Atlanta, GA 30332, USA
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.
Key words: functional modeling, design, adaptation, reuse of experiences, environ-mental interactions.
1 DEVICES AND THEIR ENVIRONMENTS
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.
1.1 Functional modeling for design
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
address the tasks required to be performed during theprocess of designing the artefact.
(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.
(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.
(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.
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
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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
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
(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
(2) Levels of intention: the functions vary in the level ofabstraction of function in terms of its meaning.
(3) Functional decomposition: a function of an artefactis decomposed into subfunctions, where each sub-function is mapped onto different aspects of theartefacts.
(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
(5) Representing function in context: functionalrepresentations that explicitly embed an artefactinto its environment.12
1.2 Functional modeling for adaptive design
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.
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
spaces for designing new devices can be generated provideda functional model has the following properties.
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.
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.
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.
The following aspects of the SBF models enablelocalization and isolable modification properties to besatisfied.
(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.
(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.
(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.
(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.
Many functional models possess one or two of the aboveproperties,2123 but not all. SBF models provide a powerfulsolution for adaptation problems.
418 S. Prabhakar, A. K. Goel