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4.40 Method Category "System Behavior Models" (SBM)  

  4.40 Methodenkategorie "Systemverhaltensmodelle" (SVM)

Contents  
  • 1 Identification/Definition of the Method
  • 2 Brief Characteristic of the Method
  • 3 Limits of the Methods Application
  • 4 Specification of the Methods Allocation
  • 5 Interfaces
  • 6 Further Literature
  • 7 Functional Tool Requirements
  • 1 Identification/Definition of the Method

    SBM is a category of methods; the individual applicable behavior models are described in more detail SBM - System Behavior Models (in Annex) by listing the selection criteria. A special method is only defined within the scope of the operationalization.

    /Davis, 1988/ can be used as an overview description.

    2 Brief Characteristic of the Method

    Objective and Purpose

    The objective of method SBM is to define the requirements for the dynamic behavior of a system by means of a model. Particular attention is paid to the influence of (external) events on the system and to possible concurrent processes within the system. This model is particularly applied for the adjustment and definition of the requirements (completeness, uniqueness, etc.) in connection with the user.

    Means of Representation

    The means of representation for SBM are structured into

    1. Representation of the static structure of the behavior via a model,
    2. representation of dynamic sequences and relevant (process) scenarios by means of a case reachability graph.
    Both network representations and representations of (communicating) automata are used as means of representation for a). They comprise the representation of events, states, actions, and conditions, and possibly of other information in form of special inscriptions for individual elements. The concurrency of individual states/actions is also represented in the model.

    According to b), this static module structure is completed by the representation of (process) scenarios which reflect a chronological and/or causal-logical sequence of possible combinations of events, states, and actions. On this basis the required or undesirable characteristics can be analyzed in the dynamic sequence*). In this connection, the scenarios correspond to the possible handling of the appropriate case/reachability graph of the model.

    Operational Sequence

    The realization of the method basically comprises the following steps (the corresponding order is to be considered as an example; individual steps can also be concurrently taken):

    1. Generation of the model by listing the elements and inscriptions (generally recommended, based on the complexity only those cases have to be modeled that are essential for the definition of the required or undesirable characteristics) relevant for the required characteristics (related to the criticality level).
      Note: The formalization by the model allows the specification of syntactic characteristics like structure consistency, branch determination, etc. already at this point.
    2. Identification of how and where the critical cases and characteristics are represented in the actual model.
    3. Specification of relevant process scenarios based on which the required characteristics can be analyzed during the dynamic sequence. In this connection, either the case or the reachability graph are the starting point. Based on an initial system state, the number of possible events and the possible succeeding states and actions are taken into consideration.
    4. An (informal) analysis of the model as well as of the process scenarios must be realized according to the specified semantic interpretation rules. The analysis concentrates on the ability to visualize and to reconstruct the relevant processes, by taking into consideration and backing up the required characteristics. If necessary, the model has to be corrected or updated in order to state the requirements more precisely in agreement with the user.

    3 Limits of the Methods Application

    Method SBM is applied if the system in question is a realtime system or respectively a distributed system, and if the criticality is high. For large models, tool support is required.

    4 Specification of the Methods Allocation

    No. Activity Description
    4.1 SD1.5 - User-Level System Structure Method SBM is applied on system level so the relevant (with regard to criticality) system parts and functions and the relevant environment of the system are taken into consideration in the modeling and in the analysis. The method covers subproduct User Requirements.Description of the Functionality with regard to those function courses that are concerned with criticality.
    4.2 SD3.3 - Definition of Requirements for the Functionality Method SBM is applied on SW level if the requirements with regard to the criticality-by inheritance of criticality-as an refinement of individual DP functions are to be described in more detail on this level. This is particularly the case if the SW/HW Units thus interact with other configuration items which results in a special behavior on this level and which has not yet been modeled on the higher levels. The method covers subproduct Technical Requirements.Overall Function of Element with regard to all those functional courses that have been concerned with criticality.

    5 Interfaces

    - not applicable -

    6 Further Literature

    /Baumgarten, 1990/ Petri-Netze, Grundlagen und Anwendungen
    /Davis, 1988/ A Comparison of Techniques for the Specification of External System Behavior
    /Harel, 1987/ Statecharts: A Visual Formalism for Complex Systems
    /Reisig, 1985/ Systementwurf mit Netzen
    /Reisig, 1986/ Petrinetze, eine Einführung

    7 Functional Tool Requirements

    SSD08 - Supporting Modeling of Function Dynamics

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