Functional modeling is in use for the interpretation of the results of model based simulation of engineered systems for design analysis, enabling the automatic generation of a textual design analysis report that expresses the results of the simulation in terms of the system’s purpose. We present a novel functional description language that increases the expressiveness of this approach, allowing a system function to be decomposed in terms of subsidiary functions as well as required effects, increasing the range both of systems and design analysis tasks for which the approach can be used. 

Bell, Jonathan

Price, Chris

Snooke, Neal

English

Functional modeling is in use for the interpretation of the results of model based simulation of engineered systems for design analysis, enabling the automatic generation of a textual design analysis report that expresses the results of the simulation in terms of the system’s purpose. We present a novel functional description language that increases the expressiveness of this approach, allowing a system function to be decomposed in terms of subsidiary functions as well as required effects, increasing the range both of systems and design analysis tasks for which the approach can be used

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Aberystwyth UniversityA language for functional interpretation of model based simulationBell, Jonathan; Snooke, Neal; Price, ChrisPublication date:2005Citation for published version (APA):Bell, J., Snooke, N., & Price, C. (2005). A language for functional interpretation of model based simulation. 1547-1548.General rightsCopyright and moral rights for the publications made accessible in the Aberystwyth Research Portal (the Institutional Repository) areretained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by thelegal requirements associated with these rights.            • Users may download and print one copy of any publication from the Aberystwyth Research Portal for the purpose of private study orresearch.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the Aberystwyth Research PortalTake down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.tel: +44 1970 62 2400email: is@aber.ac.ukDownload date: 18. Apr. 2020A language for functional interpretation of model based simulationJonathan Bell, Neal Snooke and Chris PriceDepartment of Computer Science, University of Wales AberystwythPenglais, Aberystwyth, Ceredigion, SY23 3DB, U. K.jpb, nns, cjp@aber.ac.ukAbstractFunctional modeling is in use for the interpretationof the results of model based simulation of engi-neered systems for design analysis, enabling the au-tomatic generation of a textual design analysis re-port that expresses the results of the simulation interms of the system’s purpose. We present a novelfunctional description language that increases theexpressiveness of this approach, allowing a systemfunction to be decomposed in terms of subsidiaryfunctions as well as required effects, increasing therange both of systems and design analysis tasks forwhich the approach can be used.1 IntroductionThe automation of the design analysis of engineered systemsrequires both simulation of the behavior of the system and in-terpretation of the results, to enable the automatic generationof a draft report outlining the results of the design analysis.This report is cast in terms of the system’s purpose and assystem function can be regarded as relating its behavior topurpose, this interpretation of simulation for automatic reportgeneration is a useful roˆle of functional description.Functional modeling has been used for deriving the behav-ior of a system from knowledge of its structure and compo-nent functions [Sticklen and Chandrasekaran, 1989], support-ing design by functional refinement [Iwasaki et al., 1993],and interpretation of simulation for automatic report genera-tion [Price, 1998] where system functions are associated withsignificant behaviors (outputs or goal states). Here we presenta novel language for the description of system function thatincreases the expressive power of that approach by allow-ing partial fulfilment of a system’s purpose to be described.Novel features of the language also increase both the rangeof systems that can be described and the range of tasks forwhich the language is useful.2 Describing and decomposing functionThe definition of function that underlies the language pre-sented here might be given informally as “how a deviceachieves its purpose” or more formally asFunction: An object O has a function F if itachieves an intended goal by virtue of some exter-nal trigger T resulting in the achievement of an ex-ternal effect E.This is distinct from notions of behavior and purpose, whichis a problem with some definitions of function used in modelbased reasoning. It follows that a representation of functionhas three elements; a description of purpose and the func-tion’s trigger and effect. The trigger and effect are Booleanexpressions and act as the recognizer of achievement of thefunction. A function can fail in two ways. Either the triggercan fail to result in the expected effect or the effect can oc-cur without the trigger, as summarized in Table 1. The fourTrigger Effect Functionfalse false Inoperativetrue false Failedfalse true Unexpectedtrue true AchievedTable 1: Achievement of function using trigger and effect.states of a function are defined in terms of the truth of thetrigger and effect, so if a function is triggered but the effect isnot present it is said to be failed, for example. Agreement invalue between the trigger and effect is consistent with correctbehavior of the system. We cannot, however, pair off thesecases as the consequences of the two inconsistent behaviorswill differ and the resulting report must reflect this.The description of purpose is separate from the functionaldescription itself. This is consistent with the idea that func-tion is concerned with how a purpose is fulfilled rather thanthe purpose itself and also encourages model reuse as similarpurposes might be fulfilled by systems with different func-tional requirements, such as cars’ and motorbikes’ lightingsystems.A function might depend on more than one trigger and ef-fect so logical operators can be used to describe the requiredcombinations. Alternatively, a function can be composed ofsubfunctions, each with its own trigger, effect and purpose.This distinction allows cases where the achievement of onesubfunction mitigates failure of the top level function, such aswhere a warning system has visual and audible signals and thepresence of either one means at least some warning is given.Decomposition in terms of functions means that the top levelfunction’s states must be derived from the four possible statesof each of the subfunctions. This is shown in Table 2. TheChild 1 Child 2 AND OR XORI I I I II A I A AI Fa (I) Fa FaI U (I) U UA A A A IA Fa Fa (A) (U)A U U (A) FaFa Fa Fa Fa (I)Fa U (I) (A) (A)U U U U (I)Table 2: States of functions and sub-functions.rule is that triggering of the top level function is derived fromthe triggering of the children and achievement of its effectfrom those of the children. So, for example, in the sixth lineof the table, where Child 1 is achieved (both trigger and effectare true) and Child 2 failed (trigger true but effect false) a toplevel function that depends on Child 1 AND Child 2 has failedas it is triggered (Child 1 trigger AND Child 2 trigger is true)but the effect is not achieved as Child 1 effect AND Child 2effect resolves to false. Where the state of the function is inbrackets, the report will ignore the top level function and in-clude the associated failure of the child function. In additionto the logical operators, a functional description might usethe sequential operators described in [Bell and Snooke, 2004]to allow systems whose function depends on intermittent orsequential behaviour to be described.As there are three elements in a complete functional rep-resentation, there are three possible pairs that can be used asincomplete subfunctions to simplify the functional decompo-sition. As pairing trigger and purpose (with no effect) is un-necessary, this leaves two classes of incomplete function thatcan usefully be incorporated into the language. These arePurposive incomplete function (PIF) maps effect to pur-pose. This can be used when several subfunctions sharea trigger, as in the warning example mentioned above.Operational incomplete function (OIF) maps trigger to ef-fect with no distinct purpose. It ensures a trigger is as-sociated with a specific effect where alternative combi-nations of trigger and effect can achieve some purpose.These are only used as subsidiary (child) functions.3 Example of functional descriptionThe following is (part of) the functional description of a car’sseat belt reminder system that warns the driver if either frontseat is occupied with its seat belt unbuckled.FUNCTION belt_warningACHIEVES unbuckled_warningBYvehicle movingAND (driver_unbuckled OR(passenger_present ANDpassenger_unbuckled))TRIGGERSPIF warning_lamp AND PIF chimerPURPOSE unbuckled_warningDESCRIPTION "Warn seat belt is unbuckled"FAILURE_CONSEQUENCE"No warning given of dangerous state"The PIFs and their associated purpose descriptions are, likethe description of purpose shown, separate entities. The de-composition in this example allows the language to distin-guish the case where one of the PIFs fails from the more se-rious case where both fail so no warning is given. In additionto this increased expressiveness the explicit inclusion of thetrigger differs from the language in [Price, 1998] and allowsunambiguous description of functions that are triggered bythe state of some other system function, increasing the rangeof systems that can be modeled. The trigger and the use of la-bels for trigger and effect allow a more precise specificationof required system behavior than the earlier language usedfor functional labeling. They also enable the functional de-scription to be built independently of a target system, so thelanguage for can be used for functional refinement of designin addition to interpretation of model based simulation.4 ConclusionThe functional description language introduced here in-creases both the expressiveness and range of the languageused for functional labeling in [Price, 1998]. It shares theadvantages of simplicity, reusability and capability claimedfor that language and in addition allows the functional modelto be constructed independently of the system, so supportingthe use of the language in functional refinement of a designas well as for interpretation of simulation.References[Bell and Snooke, 2004] Jonathan Bell and Neal A. Snooke.Describing system functions that depend on intermittentand sequential behavior. In Proceedings 18th InternationalWorkshop on Qualitative Reasoning, QR2004, 2004.[Iwasaki et al., 1993] Yumi Iwasaki, R. Fikes, M. Vescovi,and B. Chandrasekaran. How things are intended to work:Capturing functional knowledge in device design. In Pro-ceedings of 13th International Joint Conference on Artifi-cial Intelligence, pages 1516–1522, 1993.[Price, 1998] Christopher J. Price. Function-directed electri-cal design analysis. Artificial Intelligence in Engineering,12(4):445–456, 1998.[Sticklen and Chandrasekaran, 1989] Jon Sticklen andB. Chandrasekaran. Integrating classification-basedcompiled level reasoning with function-based deep levelreasoning. In Werner Horn, editor, Causal AI Models,Steps Toward Applications, pages 191–220. HemispherePublishing Corporation, 1989.

A language for functional interpretation of model based simulation

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