In the 1970s, Allan Albrecht and his colleagues at IBM measured a number of projects using both logical source code statements and function point metrics. These pioneering studies found some interesting but imperfect correlations between source code size and function points for many programming languages. In 1984, based upon research by Capers Jones, SPR began publishing a table of these empirically-derived relationships, termed "backfiring ratios." FP values come in small groups of three, four, or more, depending on the functional type and relative complexity. So it should be apparent that backfiring is at best theoretical. However, there is some benefit in the rough approximation provided with the backfire ratios provided.
The table currently includes over five hundred source code languages. Use of this data is subject to a number of caveats driven by its derivation and nature. Backfired function point counts are of lower accuracy than normal function point counts. Backfiring is ambiguous if the starting point is physical lines of code, and its accuracy is further compromised in sizing of mixed-language applications. Backfiring ratios vary based on individual programming styles and numerous. The accuracy of this approach is less than that of counts by certified personnel, but the speed and ease of generating results continue to make this approach popular, particularly with legacy applications.
The Programming Languages Table includes a white paper describing the SPR approach in detail, and a full explanation of the ratings. It is available at no cost to SPR KnowledgePLAN® licensees under active maintenance. Request a copy via email with your product serial number. Other customers can purchase via the SPR Catalog
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