ABSTRACT FOCUS AND CAUSAL REASONING IN DISTURBANCE MANAGEMENT OF COMPLEX DYNAMIC SYSTEMS
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FOCUS AND CAUSAL REASONING IN DISTURBANCEMANAGEMENT OF COMPLEX DYNAMIC SYSTEMS
Johannes PETERSENTechnical University of DenmarkDepartment of Automation, B. 326DK-2800 Lyngbyjop@iau.dtu.dk
ABSTRACTIn disturbance management of complex dynamicsystems causal reasoning plays an important role.This paper provides a theoretical discussion ofsome aspects of causality and causal reasoning.More specifically, it deals with the notion of acausal field and focus in causal reasoning. Bymeans of simple examples it is shown how twodifferent strategic response types in disturbancemanagement, repair and compensation, imposes adifferent focus in causal reasoning.
KEYWORDSCausal Reasoning, Focus,Disturbance Management and Diagnosis.
INTRODUCTIONOne of the tasks of the human operator supervisinga complex process plant is to respond appropriatelyto disturbance situations. When an unfamiliardisturbance occurs the operator is faced with an ill-structured problem characterized by a mismatchbetween the actual and the desired behavior.Typically the goal to pursue is not readily known atthe time a disturbance is detected.Disturbance management of complex dynamicsystems cannot be reduced to an identification offailed components for the purpose of repair. In factthe primary task of the operator is to cope withshort-term consequences of the disturbancebringing the system into a safe state. Only whenthis is accomplished it is feasible to diagnose andtreat the underlying fault (e.g. (Rasmussen, 1986)).In response to an unfamiliar disturbance situationthe operator has to consider several possiblestrategic response types (see e.g. (Rasmussen,1986) and (Woods, 1988)):1. Compensate disturbance2. Compensate consequences of the disturbance3. Shut-Down4. Repair (find and correct, what produced thedisturbance)The choice of a specific strategy should be derivedon the basis of an overall assessment of thesituation. Typically such an assessment will haveto consider aspects such as: 1) the kind ofdisturbance, 2) its possible consequences inrelation to overall system goals, 3) the availableactions and 4) time resources.As it cannot be assumed that the informationneeded to carry out a proper assessment anddiagnosis of the situation is readily given, theoperator has to make inferences based on the plantstate information available on the display as well ashis or her mental models of the process. From anabstract point of view it is essential for each of thedifferent response types, mentioned above, toidentify causal factors, which by propermanipulation, will bring about the desired effect.
If the overall goal is repair, the operator searchesfor causal factors in terms of possiblemalfunctioning components, which could havecaused the specific abnormal symptoms.Depending on the available means the component,which is found to be malfunctioning, is exchangedor its workings adjusted. When a repair task is setout it has to be ensured that the process is in a safestate, i.e. the current state of the process will haveno immediate undesired consequences.
If the overall goal is to compensate a specificdisturbance the operator seeks to identify possiblecausal factors which, when manipulated properly,will lead to a compensation of the disturbance orsome of its consequences. Compensation is ameans to cope with the consequences of adisturbance, which have a negative influence onsome of the goals ascribed to the system.
It is clear that causal reasoning plays a major rolein disturbance management for which the overallpurpose is to make a link between analysis of thestate of the process and synthesis of plans ofintervention. At the same time causal reasoningand the nature of causality raises difficult problemswhich has been subject to discussions withinphilosophy (e.g. (Sosa, 1975)), philosophy ofmedicine (Wulff et al., 1986), qualitative physics(e.g. (Forbus, 1984) and (De Kleer et al., 1984)),and cognitive science and man-machine systemsresearch (e.g. (Rasmussen, 1991), (Pedersen et al.,1991), (Rasmussen, 1993), (Pedersen et al., 1993)).
As emphasized by Pedersen and Rasmussen(Pedersen et al., 1991) it is important to make adistinction between singular causation and generalcausation. General causation describes relationsbetween event types, whereas singular causationdescribes relations between particular events.Disturbance management and diagnostic reasoningis primarily concerned with making inferencesbetween particular events, such as “the feedwaterpump 12 has failed” or “the flow in pipe P1 hasdecreased”. That is, singular causal relations aresought between events referring to properties of thespecific process being supervised. In this paper aspecific theory of singular causality, developed byMackie (Mackie, 1975) and further developed byPedersen et al. (Pedersen et al., 1993), is described.This theory of singular causality will be used tothrow light on some aspects of causal reasoningwhich are particularly important for disturbancemanagement of complex dynamic systems. Morespecifically, two response types in disturbancemanagement, repair and compensation, are studiedby means of simple examples. It is analyzed howcausal reasoning for the purpose of repair andcompensation imply a different focus in relation tothe kinds of cause factors searched for.
