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4.21 Elementary Method "Control Flow Modeling" (CFM)  

  4.21 Elementarmethode "Kontrollflu -Modellierung" (KFM)

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

    /Hatley, 1987/ Appendix A, A.2 and A.3 (pp. 363-381)

    2 Brief Characteristic of the Method

    Objective and Purpose

    The method Control Flow Modeling (CFM) is used to supplement control elements in the data flow diagrams generated in the data flow modeling. These updates have been proved necessary and useful, particularly within the scope of the realtime-oriented programming. The interaction of processes introduced in the data flow modeling are described by means of control flow diagrams. In the following the term "Processes" only refers to these processes.

    Means of Representation

    Control flows connect elements of the control flow diagram with each other. They transport control signals. Control stores are allocated the same role in control flow diagrams as data stores in data flow diagrams: they temporarily store the content of control flows without changing them.

    The interface to the control specification (CSPEC interface) is identified by a symbol (e. g. bar) per control flow diagram. In this connection it is mentioned if a process is activated or deactivated depending on CSPEC (e. g. by an arrow from a CSPEC interface to a process) and if an activated process works as an input value in the CSPEC (e. g. by an arrow from a process to a CSPEC interface) (see chapter 5 "Interfaces").

    Operational Sequence

    The control specification (CSPEC) is the steering element of the control flow model. This describes the interactions of processes by control flows. A CSPEC lists the conditions under which a process is activated or deactivated. Generally, the control specification is realized by a finite automaton with output (Mealy automaton, see basic method STM), therefore a further description of the control specification is not given at this point.

    The most effective way to utilize method CFM is in connection with the development of a mostly data-oriented system with an additional control component. In this connection, the term "data-oriented" does not only refer to a typical database application. It rather refers to the fact that the decomposition of the system is based on the identification of data flows and processes, not on an event modeling. This uneven weighting between data orientation and control orientation results from the subordination of the control flow mechanism to the data flow mechanism in the diagram technique since the flow of control is only identified after the problem decomposition and according to structural aspects.

    3 Limits of the Methods Application

    The basic method Control Flow Modeling is predominantly applied-in particular in connection with event-oriented systems-if the individual processes of the DFM - Data Flow Modeling have to be specified in a more detailed manner because of a high complexity. Normally, if this high complexity does not exist, the DFM is sufficient.

    4 Specification of the Methods Allocation

    No. Activity Description
    4.1 SD3.2 - Specification of Requirements for External Interfaces of SW/HW Unit In case of a realtime-oriented application, a control flow model has to be generated in addition to the data flow model. The control flows must be defined by means of a state transition diagram.

    The result is a combined Data Flow/Control Flow model to model the technical requirements. Together with method DFM - Data Flow Modeling, the method covers the subproduct Technical Requirements.Technical Requirements for the Interfaces.

    5 Interfaces

    No. Interface Observation Information in Annex 1
    5.1 CFM-DFM Control flow models have to be generated on the basis of data flow models. The components of CFM are integrated into the corresponding data flow models. 4.5 Interface DFM-CFM
    5.2 CFM-STM The control specification CSPEC must be realized by means of a state transition diagram or by an equivalent means of representation. The state transition diagram is integrated into the control flow model. 4.14 Interface CFM-STM

    6 Literature

    /Hatley, 1987/ Strategies for Real-Time System Specification
    /Raasch, 1991/ Systementwicklung mit Strukturierten Methoden

    7 Functional Tool Requirements

    SSD07 - Supporting Modeling of Information Flows

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