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Software Estimation with Function Point Analysis September 2, 2005

Posted by Coolguy in Software Development.
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  • Function Point Analysis is an objective and structured technique to measure software size by quantifying its functionality provided to the user, based on the requirements
  • This technique breaks the system into smaller components so they can be better understood and analyzed.
  • In Function Point Analysis, systems are divided into five large classes.
  • External Inputs EI
  • External Outputs EO
  • External Inquiries EQ
  • Internal Logical Files ILF
  • External Interface Files EIF
  • First three are treated as Transactional Function Types
  • Last two are called Data Function Types

External Input (EI)

  • External Input is an elementary process in which data crosses the boundary from outside to inside.
  • This data may come from a data input screen or another application.
  • The data may be used to maintain one or more internal logical files.
  • The data can be either control information or business information.

External Output (EO)

  • External Output is an elementary process in which derived data passes across the boundary from inside to outside.
  • Additionally, an EO may update an internal logical file
  • The data creates reports or output files sent to other applications. These reports and files are created from information contained in one or more internal logical files and external interface files

External Inquiry (EQ)

  • External Inquiry is an elementary process with both input and output components that results in data retrieval from one or more internal logical files and external interface files

Internal Logical File (ILF)

  • Internal Logical File is a user identifiable group of logically related data that resides entirely within the application boundary and is maintained through External Inputs

External Interface File (EIF)

  • External Interface File is a user identifiable group of logically related data that is used for reference purposes only.
  • The data resides entirely outside the application boundary and is maintained by external inputs of another application.
  • That is, the external interface file is an internal logical file for another application.

Objectives of Function Point Analysis

  • Function Points measure systems from a functional perspective and are independent of technology.
  • Hence, regardless of technology, language, development method, or
    hardware/software used, the number of function points for a system will remain constant.
  • The variable in Function Point Analysis is the amount of effort required to deliver a given set of function points.
  • Therefore, function point analysis can be used to determine which
    environment/language/tool is more productive.
  • Function point analysis can provide a mechanism to track and monitor scope creep.
  • Function point counts at the end of each phase/stage of a project can be compared to the function points actually delivered.
  • If the number of function points has increased then there has been a scope creep.
  • The number of function points that has increased or decreased defines the project growth.
  • If the project has grown then it is a sure indication that the requirements haven’t been gathered well and there has been some scope creep.

Process of Counting Function Points

  • Determine the application boundary
  • Identification of the data functions (internal logical files and external interface files)
  • Identification of transactional functions (external inputs, external outputs and external inquiries)
  • Calculation of the Unadjusted Function Point (UAF) Count
  • Determination of the Value Adjustment Factor (VAF) using General SystemCharacteristics (GSC)
  • Finally, calculate the adjusted Function Point count
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