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Living with Function Points

Learn how to count function points and measure functionality in business applications using Function Point Analysis (FPA), a reliable and independent measurement approach. Discover the different elements that are counted, such as outputs, inquiries, inputs, files, and external interfaces. Understand the weightings for each feature and the importance of considering factors like backup and recovery, data communications, distributed processing, performance, and operational environment. Also, explore questions related to online data entry, master file updates, complexity, reusability, conversion and installation, and design for change and user ease. Finally, find out how adjusted function points provide a more accurate prediction of software size compared to traditional source lines of code (SLOC) measurement.

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Living with Function Points

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  1. Living with Function Points Bernstein and Lubashevsky Text pp234-238

  2. Function Point Analysis How to count function points

  3. Function Points • Attempting to measure “functionality” • widely used in business applications

  4. Program Features • outputs • inquiries • inputs • files • external interfaces

  5. Pressman, Soft Eng, 5th Ed • Outputs • “Each user output that provides application-oriented information to the user is counted. In this context output refers to reports, screens, error messages, and so on. Individual data items within a report are not counted separately”

  6. Pressman, Soft Eng, 5th Ed • Inputs • “Each user input that provides distinct application-oriented data to the software is counted. Inputs should be distinguished from inquiries, which are counted separately” • Inquiries • “An inquiry is defined as an on-line input that results in the generation of some immediate software response in the form of an on-line output. Each distinct inquiry is counted.”

  7. Pressman, Soft Eng, 5th Ed • Files • “Each logical master file (I.e. a logical grouping of data that may be one part of a large database or a separate file), is counted” • External interfaces • “All machine readable interfaces (e.g. data files on tape or disk) that are used to transmit information to another system are counted.”

  8. Dreger, FPA, 1989 • “A function point is defined as one end-user business function” • “business functions made available to the user are identified” • “outputs are items of business information processed by the computer for the end user”

  9. Dreger, FPA, 1989 • Inquiries “are direct inquiries into a data base or master file that look for specific data, use simple keys, require immediate response and perform no update functions” • “Inputs are items of business data sent by the user to the computer for processing and to add, change, or delete something.” • “Files are data stored for an application, as logically viewed by the user”

  10. Dreger, FPA, 1989 • Outputs • “count each of the outputs leaving the context diagram ‘area under study’ at the lowest (greatest detail) level of the logical … data flow diagram system” • count separately if different format or different processing • Dreger says detail lines and total lines are different, ifpug says no

  11. Dreger, FPA, 1989 • Inputs • “count each unique user data or control input that enters the application boundary and also updates (adds to, changes, or deletes from) a logical internal file, data set, table or independent data item.” • “count as one input each uniquely formatted or processed portion ...”

  12. Dreger, FPA, 1989 • Files • “count each major logical group of user data or control information” • Interfaces • “count as one interface each major logical .. file or other logical group of user-approved data or control information within the application boundary that is set to, shared with, or received from another application.”

  13. Weights for features • simple average complex • outputs 4 5 7 • inquiries 4 5 7 • inputs 3 4 6 • files 7 10 15 • interfaces 5 7 10

  14. Questions • Does the system require reliable backup and recovery? • Are data communications required? • Are there distributed processing functions? • Is performance critical? • Will the system run in an existing, heavily utilized operational environment?

  15. Questions • Does the system require on-line data entry? • Does the on-line data entry require the input transaction to be built over multiple screens or operations? • Are the master files updated on-line? • Are the inputs, outputs, files, or inquiries complex? • Is the internal processing complex?

  16. Questions • Is the code designed to be reusable? • Are conversion and installation included in the design? • Is the system designed for multiple installations in different organizations? • Is the application designed to facilitate change and ease of use by the user?

  17. Adjusted Function Points • FP = FPunadjusted * (.65 + 0.01 * (sum of ratings ) )

  18. AT&T and FPA • “5. The measurements must be repeatable and independent of the observer” • “The prediction accuracy proved to be better than twice of traditional SLOC”

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