Real Time Systems Design And Analysis

Chapter 8 - Engineering Considerations

8.1   METRICS

Metrics can be used in real-time systems engineering in several ways. First,
certain metrics can be used during software requirements development to assist
in cost estimation. Another useful application for metrics is for benchmarking. For
example, if an engineering group has a set of successful systems, then computing
metrics for those systems yields a set of desirable and measurable characteristics
with which to seek or compare in future systems. Most metrics can be used for
testing in the sense of measuring the desirable properties of the software and
setting limits on the bounds of those criteria.

Of course, metrics can be used to track project progress. In fact, some companies
reward employees based on the amount of software developed per day as
measured by some of the metrics to be discussed (e.g., delivered source instructions,
function points, or lines of code). Finally, metrics can be used during the
testing phase and for debugging purposes to help focus on likely sources of errors.


8.1.1   Lines of Code

The easiest characteristic of software that can be measured is the number of
lines of finished source code. Measured as thousands of lines of code (KLOC),
the “clock” metric is also referred to as delivered source instructions (DSI) or
noncommented source-code statements (NCSS). That is, the number of executable
program instructions, excluding comment statements, header files, formatting
statements, macros, and anything that does not show up as executable code after
compilation or cause allocation of memory, are counted. Another related metric
is source lines of code (SLOC), the major difference being that a single source
line of code may span several lines. For example, an if-then-else statement
would be a single SLOC, but multiple delivered source instructions.

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