Analysis Techniques For Man-Machine Systems Design
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Analysis Techniques For Man-Machine Systems Design

Analysis Techniques For Man-Machine Systems Design Analysis Techniques For Man-Machine Systems Design

ai.eecs.umich.edu
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11.07.2015 Views

NATO UNCLASSIFIED EAC/243(Panel 8 TR/7Volume 2- 36 -orderconfirmationmmunication order is processing operator 1 communication order is sent toorder arrives waiting starts is active is terminated complete sendsystem is idle,waiting for ordersr communication order order operator 2 communication order is con tiocommnicaionordeissenttoorder arrives waiting processing is active is terminated complete cstartscommandstartsFigure 2.10:A Petri net model of a communication system in a conflict situationTable 2.4: Some typical interpretations of Transitions and Places (Murata, 1989)Input places Transition Output placesPreconditions Event Post-conditionsInput data Computation step Output dataInput signals Signal processor Output signalsResources needed Task or job Resources releasedConditions Clause in logic ConclusionsBuffers Processor BuffersInputs to the techniqueThe events and the conditions of a system must bedescribed and modelled. The sequencing between theevents must be available, as well as their prioritiesand duration times.Outputs of the techniqueThe execution of the Pctri net results in a sequence ofdiscrete events that can be analysed. Further, severaltechniques have been developed for analyzing Pctri netswithout execution of the neL Some typical questions thatcan be addressed by this type of model are:1. Reachability of certain markings, i.e., unsafe systemstates.2. Resource administration and allocation, i.e., overflowand conflict situations, and deadlock problems and"starvation" of the system.When to usePetri nets can be used in the latter stages of design definition, or when other systems engineering specialities havemade them available.NATO UNCLASSIFIED- 36-

NATO UNCLASSIFIED- 37 - AC/243(Panel-8)TR/ 7Volume 2Related techniquesPetri nets are related to Function Flow Diagrams (2.1), SADTrm/IDEF (2.3), Finite State Machines (see 2.5), DataFlow Diagrams, and Behaviour Graphs (2.7)Resources requiredThe analyst must obtain information concerning the expected behaviour of the system. A user-defined scenario is atypical starting point. A CASE tool is mandatory in order to record different relationships systematically (e.g.,between functions and items, between functions and requirements) and to handle the iterative development of thedescription effectively.DisadvantagesAdvantagesA Petri net model can be considered as an alternative to a Petri nets tends to become too large for analysis of evenstate machine model and is specially suited to modelling modest systems. In applying Petri nets it is oftena-synchronous concurrent systems. Petri nets can be used necessary to add special modifications or restrictionsfor the hierarchical decomposition of systems and for suited to the particular application (Murata. 1989).developing models for SAINT simulation (5.2). Petri netmodels can used by practitioners and analysed formally bytheoreticians. The modeling power of a Petri net can beextended in several ways (Christensen, 1991).Relative contributionNo data available.ApplicationsPetri nets can be used to describe behaviour where ambiguity cannot be tolerated (e.g., a life-critical application) orwhere precise process synchrony is important. Petri nets have bccn used for specifying man-machine dialogues whichinvolve asynchronous events and interleaving (mixed command sequences) (Biljon, 1988). They have been applied todecision making (Perdu & Levis. 1989) and to command and control systems (Wohl, 1987; Wohl & Tenney, 1987).Petri nets have also been proposed as a means of evaluating operator workload (Madni & Lyman. 1983) by defininghuman operator tasks as places, and internal or external forcing events as transitions.Quality assurance considerationsPetri nets check for consistency, completeness. and potential conflicts in concurrent operations. Dynamic consistencycan be checked using simulation techniques.Relationship to system performance requirementsPerformance requirements are specified as an integral part of the model. It is possible to associate deterministic orNATO UNCLASSIFIED- 37 -

NATO UNCLASSIFIED- 37 - AC/243(Panel-8)TR/ 7Volume 2Related techniquesPetri nets are related to Function Flow Diagrams (2.1), SADTrm/IDEF (2.3), Finite State <strong>Machine</strong>s (see 2.5), DataFlow Diagrams, and Behaviour Graphs (2.7)Resources requiredThe analyst must obtain information concerning the expected behaviour of the system. A user-defined scenario is atypical starting point. A CASE tool is mandatory in order to record different relationships systematically (e.g.,between functions and items, between functions and requirements) and to handle the iterative development of thedescription effectively.DisadvantagesAdvantagesA Petri net model can be considered as an alternative to a Petri nets tends to become too large for analysis of evenstate machine model and is specially suited to modelling modest systems. In applying Petri nets it is oftena-synchronous concurrent systems. Petri nets can be used necessary to add special modifications or restrictionsfor the hierarchical decomposition of systems and for suited to the particular application (Murata. 1989).developing models for SAINT simulation (5.2). Petri netmodels can used by practitioners and analysed formally bytheoreticians. The modeling power of a Petri net can beextended in several ways (Christensen, 1991).Relative contributionNo data available.ApplicationsPetri nets can be used to describe behaviour where ambiguity cannot be tolerated (e.g., a life-critical application) orwhere precise process synchrony is important. Petri nets have bccn used for specifying man-machine dialogues whichinvolve asynchronous events and interleaving (mixed command sequences) (Biljon, 1988). They have been applied todecision making (Perdu & Levis. 1989) and to command and control systems (Wohl, 1987; Wohl & Tenney, 1987).Petri nets have also been proposed as a means of evaluating operator workload (Madni & Lyman. 1983) by defininghuman operator tasks as places, and internal or external forcing events as transitions.Quality assurance considerationsPetri nets check for consistency, completeness. and potential conflicts in concurrent operations. Dynamic consistencycan be checked using simulation techniques.Relationship to system performance requirementsPerformance requirements are specified as an integral part of the model. It is possible to associate deterministic orNATO UNCLASSIFIED- 37 -

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