Time management for real-time systems
Loïc Briand · ACM SIGAda Ada Letters · 1992
The external time is the space used for the definition of dates in their common meaning.The use of external time in software is reserved to direct relationship of application with real world dates, such as an airplane departure time information ("the next flight leaves at 5:23 A.M.").The main characteristic of the external time is that it is not monotonic: it is always possible to update its current value.Two kinds of reasons generally imply such an update: ° The target computer's clock source is not that accurate that a drift cannot be observed after a while.° The external world modifies its time reference: that is for example the case of daylight time.Systems that must deal with several time zones generally prefer to use one unique time reference such as GMT time.This is for example the case of air traffic control systems where it would be quite impossible to associate several different time references with the same object. Volume XlI, Number 5