Software productivity

You can measure productivity in a manufacturing system by counting the number of units that are produced and dividing this by the number of person-hours required to produce them. However, for any software problem, there are many different solutions, each of which has different attributes. One solution may execute more efficiently while another may be more readable and easier to maintain. When solutions with different attributes are produced, comparing their production rates is not really meaningful.

Nevertheless, as a project manager, you may be faced with the problem of estimating the productivity of software engineers. You may need these productivity estimates to help define the project cost or schedule, to inform investment decisions or to assess whether process or technology improvements are effective.

Productivity estimates are usually based on measuring attributes of the software and dividing this by the total effort required for development. There are two types of metric that have been used:

  1. Size-related metrics These are related to the size of some output from an activity. The most commonly used size-related metric is lines of delivered source code. Other metrics that may be used are the number of delivered object code instructions or the number of pages of system documentation.
  2. Function-related metrics These are related to the overall functionality of the delivered software. Productivity is expressed in terms of the amount of useful functionality produced in some given time. Function points and application points are the best-known metrics of this type.

Lines of source code per programmer-month (LOC/pm or SLOC/pm) is a widely used software productivity metric. You can compute LOC/pm by counting the total number of lines of source code that are delivered, then divide the count by the total time in programmer-months required to complete the project. This time therefore includes the time required for all other activities (requirements, design, coding, testing and documentation) involved in software development. However, the number of lines of source code depends on the programming language used and this can sometimes result in productivity anomalies.

This approach was first developed when most programming was in older programming languages such as FORTRAN, assembly language or COBOL. Then, programs were typed on cards, with one statement on each card. The number of lines of code was easy to count: It corresponded to the number of cards in the program deck. However, programs in languages like Java or C++ consist of declarations, executable statements and commentary. They may include macro instructions that expand to several lines of code. There may be more than one statement per line. There is not, therefore, a simple relationship between program statements and lines on a listing.

Individual programmer productivity is affected by a range of factors and it does not always follow that the programmer who produces the most lines of code is the most productive. As a manager, you should not use productivity measurements to make hasty judgements about the abilities of the engineers on your team. If you do, engineers may compromise on quality in order to become more ‘productive’. It may be the case that the ‘less productive’ programmer produces more reliable code, code which is easier to understand and cheaper to maintain. You should always, therefore, think of productivity measures as providing partial information about programmer productivity. You also need to consider other information about the quality of the programs that are produced.

(c) Ian Sommerville 2008