ALLAN J. ALBRECHT AND JOHN E.GAFFNEY,JR., MEMBER ,IEEE published in November 1983. Software Function, Source Lines Of Code, and Development Effort Prediction: A Software Science Validation. Presented By: Mohammod Saifur Rahman. Introduction.
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ALLAN J. ALBRECHT AND JOHN E.GAFFNEY,JR., MEMBER ,IEEEpublished in November 1983
Software Function,Source Lines Of Code, andDevelopment Effort Prediction:
A Software Science Validation
Presented By: Mohammod Saifur Rahman
The Problem:Predicting the size of a programming system and its development effort is one of the most important problems faced by the developers.
The Solution:In this article, Albrecht claims that this prediction can be made by estimating the amount of functions a software is to perform.
Albrecht then adds that this “amount of functions” can be estimated by the amount of data used or to be generated by the software.
Amount of function
The amount of function is measured by “Function Points”, which is a weighted sum of number of (1) inputs, (2) outputs, (3) master files and (4) inquiriesprovided to or generated by the software.
Albrecht has employed a methodology for validating estimates of the amount of work-effort (which he calls work-hours) needed to design and develop the software.
He listed and counted the number of external user inputs, inquires, outputs and master files to be delivered by the development project.
Each of these categories of input and output counted individually and weighted by numbers, which reflected the relative value of the function to the user/customer.
The weighted sum of inputs and outputs is called “Function Points”.
Halstead developed aSoftware Length Equation, to estimate the number of tokens or symbols in a program, as follows:
N = n log 2 n + m log 2 m
WhereN is the number of tokensor symbols constituting a program, n is the operator vocabulary size , and m is the operandor data label vocabulary size.
Thus the number of tokens in a program consisting of a several functions or procedures is best found by applying the size equation to each function procedure individually and summing the results.
Gaffney applied the software length equation to a single address machine in the following way:
- A program consists of data plus instructions.- A sequence of instructions can be thought of as a string oftokens. The op.codes tokens may be referred to asoperators and data label tokensas operands. - For e.g in the instruction “LA X”, which means load accumulator with the content of location X, “LA” is theoperator and “X” is the operand.
However, the article states that in the previous equation, number of operators (n) need not be known, instead an average figure for n can be used, and thus only the number of data labels (m) will determine the number of instructions, hence thesize of the software.
This statement is also supported by Christiansen’s claim that program size is determined by the data that must be processed by the program.
Thus the data label (both inputs and outputs) size can be used to estimate the size of the software.
Table I presents data on 24 applications developed by DP services organization, as follows:1. The counts of 4 types of external input/output (In, Out, File, Inquiry) for the applications as a whole.
2. The number of function points for each program.3. The number of SLOC that implemented the function required.4. The number of work hours required to design, develop and test the application.
Using the DP Services data estimate formulas were explored as functions of 9 variates:1. Function points,2. Function Sort Content,3. Function potential Volume,4. Function Information Content ,5. I/O Count , 6. Sort Count,7. Count Information Content,8. Source Lines of COBOL, and9. Source Lines Of PL/1
Albrecht uses the following average weights to determine Function pointsNumber of inputs X 4Number of Outputs X 5Number of Inquiries X 4Number of Master files x 10As an example of the calculation, consider the data for the first application (in Table I). The number of function points calculated is equal to:F=(25 X4)+(150 x 5) +(75 X 4) +(60 x 10)=1750
In this section, the article provides a number of formulas for estimating the following:work hours and SLOC, as functions of function points.
The previous sections and related figure and tables in the
article, developed several formulas and explored theirs
consistency within the DP services data that were used to
develop the formulas.
These formulas then are also validated against three
different development sites.
Table V presents four formulas developed from the DP
services data and the statistics of their validation on the
data from the other three sites.
The very high values of sample correlation between the
estimated and actual SLOC for the 17 validation sites,
listed in Table V (i.e. > 0.92) are most encouraging!