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23 Cards in this Set
- Front
- Back
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the system failure approach
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Methods to examining the real world
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- Abstraction - Modelling - Manipulation - Evaluation |
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the failures analysis cycle
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The Systems Failures Approach has 2 key features
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- Conceptualisation and modelling of the failure situation as a system - Comparison of the system with a model of a robust system that is capable of purposeful activity without failure in order to reveal lessons about the failure. |
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Pre- analysis
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4-way balancing act is always necessary between: - The requirement being holistic, which underpins system work - The purpose of the study, - The time and cost constrains imposed by the client - And the need for the investigation to be manageable |
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Techniques of pre-analysis:
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- spray diagrams - Relationship diagrams - Multiple-cause diagrams - Rich pictures - Non-diagrammatic methods: lists, databases, charts etc. |
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Spray diagrams
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record ideas about relationships in the very early stages of analysis, often as a preliminary to drawing a relationship diagram or multiple-cause diagram.
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Rich picture
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It seeks to get onto one sheet of paper all of the salient features of a situation in a way that is insightful and can be easily assimilated.
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Relationships diagrams
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provide a snapshot of situations.Lines are drawn to connect components that are significantly related in some way.Although the nature of the relationship is not specified, different lengths of lines can be used to imply different degrees of closeness
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Modelling systems requires
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- Name and definition of the system - Description of the components of the system - Description of the components and the relationships in the environment of each system - Identification of the wider system - Description of the inputs and outputs - Identification of the system variables - The structural relationship between components to be established - Some identification of the relationship between the variables that describe the behaviour of the system |
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Input-output diagrams
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very effectively shows what the system would and should do - that is to take inputs and transform them into outputs.
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Systems failure approach
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Stage 1: pre-analysis Stage 2: identifying significant failures and select system(s) Stage 3: Modelling systems |
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Formal Model System
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- System (Formal System) - Wider system - Environment |
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The wider system
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- It defines its purpose and sets its objectives - It influences the decision-makers within the system and monitors the performance of the system as a whole. - It also provides the resources that the system needs in order to function. |
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The environment
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disturbs the system directly but it also disturbs it indirectly through the wider system.The system attempts to influence the environment directly and through the wider system.
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the relationships between the system, the wider system and the environment
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Relationships between subsystems
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The decision making system
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allows the system to exhibit choice, and thus behave as a purposeful system.
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The performance monitoring subsystem
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observing the transformation processes and reporting deviations from the expectations to the decision-making subsystem so it can initiate corrective action if it is necessary.
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Formal system model features:
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- A decision-making subsystem - A performance monitoring subsystem - A set of subsystems and elements that carry out the tasks of the system and thus effect its transformations by converting inputs to outputs - A degree of connectivity between the components - An environment with which the system interacts - boundaries separating the system from its wider system and the wider system from the environment - Resources - A continuous purpose or mission that gives rise to expectations - Some guarantee of continuity |
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Communication
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- Communication between the system and its environment - The flow of information for the wider system, via the system, to the subsystems, and vice versa - Numerous communication links within the system and the subsystem |
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the whole formal system model
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The list of recurring themes thatemerge from comparisons with the FSM is:
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Deficiencies in the structure of the system, such as a lack of aperformance-measuring subsystem or a control/decision-makingsubsystem.. No clear statements of purpose supplied in a comprehensible form to thesystem from the wider system.. Deficiencies in the performance of one or more subsystems – forexample the performance-measuring subsystem may not have performedits task adequately.. Lack of an effective means of communication between the varioussubsystems.. Inadequate design of one or more subsystems.. Not enough consideration given to the influence of the environment, andinsufficient resources to cope with those environmental disturbances thatwere foreseen.. Imbalances in resource allocation that lead to quality problems or tocost or output quantity problems or delays.
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