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Annex 1 Function Point Method (FPM)  

  Function Point Methode (FPM)

  • 1 Identification/Definition of the Method
  • 2 Brief Characteristic of the Method
  • 3 Appraisal of the Method
  • 4 Application of the Method in the V-Model
  • 5 Interfaces
  • 6 Further Information
  • 7 Literature
  • 1 Identification/Definition of the Method

    /IBM, 1985/ pp. 7-13

    2 Brief Characteristic of the Method

    The Function Point Method (FPM) was developed by IBM. It is a combination of the analog method (the FP curve is based on the empirical values from similar projects) and weighting method (evaluation of the influence factors for the project). FPM is closely related with the function-oriented development methods (like SSADM, HIPO) and-based on the user requirements-concentrates on the functions. The effort estimation takes complexity, certain software characteristics, and productivity into consideration. The Function Points (FP) are applied as a measuring means for the productivity used to specify the effort.

    FPM steps:

    1. Determination of the Function Points
      In order to determine the Function Points, the functions are defined and classified, according to external input, external output, logical internal file, external interface file, and external inquiry ("transactions"). After that, these transactions are classified according to their complexity (simple, average, complex). Based on the type and the degree of complexity, the transactions are weighted. The addition of these weights of all transactions results in the (unadjusted) Function Points.
    2. Determination of the adjusted Function Points
      Influence factors like interlacing with other projects, decentralized data management, transaction rate, complex processing, reusability, conversions, user friendliness are taken into consideration and evaluated with regard to the influence they are having on the project. The degree of influence is calculated from the sum of the influence factors. Multiplying the unadjusted function points with the degree of influence results in the adjusted function points. As compared to the (unadjusted) function points, these can be increased or reduced by up to 30 %.
    3. Determination of the Effort
      Based on a productivity curve/table, the adjusted function points are converted into man-months. To realize this, an "IBM curve" is available which should be successively replaced by individual empirical values from post-calculations.

    3 Appraisal of the Method

    Criteria for the Application of the FPM

    Strong and Weak Points of the Method and possible Remedial Measures

    4 Application of the Method in the V-Model

    5 Interfaces

    - not applicable -

    6 Further Information

    Further Developments/Versions

    The FPM has already been modified in several ways. Different versions exist with regard to

    Related Methods

    The Data Point Method was developed by Harry M. Sneed /Sneed, 1991/, i. e. as an alternative to CoCoMo and FPM and as an answer to the trend towards data- or respectively object-oriented software development.

    The procedure applied to determine the data points is similar to the one applied to determine the function points, with the difference that data objects and not transactions are concentrated on. The data point method can be applied for the estimation of commercial systems on the basis of a data model, FPM on the basis of a functional model.

    Method ASSET-R /Reifer, 1989/ determines the size and effort of a real-time system via function points. In ASSET-R, real-time-oriented influence factors like process interfaces and operating modes are taken into consideration when setting up the function points. However, ASSET-R then returns via influence factors like system architecture and programming language to the estimation basis LOC.

    7 Literature

    /Albrecht, 1983/ Comparison of the FPM with LOC-based Effort Estimation Methods
    /Busch, 1972/ Definition of the Delphi Method
    /IBM, 1985/ Original Literature (IBM Product Information)
    /Noth, 1986/ Definition and Introduction into FPM, Appraisal, Further Developments,
    and Application Proposals (pp. 89-105, p. 118)
    /Reifer, 1989/ Description of Method ASSERT-R as compared to other Estimation Methods
    /Sneed, 1987/ Explanation of the FP Method as compared to the Methods CoCoMo
    and Component Analysis Method (pp. 79-80, p. 175, pp. 178-181, pp. 185-189, pp. 195-196)
    /Sneed, 1991/ Brief Description of the Data Point Method
    /Symons, 1988/ Critical Assessment of the FPM, Improvement Proposals (Mark II)

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