Real-Time for the Real World ™
Work-in-progress preview of a work-in-progress book:
Introduction to Fundamentals of Timeliness
in General Real-Time Systems [Jensen 201x]
Informally, a system is a “real-time” one if its core properties of timeliness and predictability of timeliness are integral to its logic, not just performance measures. In general, those properties are dynamic due to intrinsic aleatory and epistemic uncertainties about parameters of the system and its application environment. Despite such uncertainties, dynamically real-time systems have mixed application-specific kinds and degrees of criticality—including even the most extreme safety-critical systems (e.g., for warfare)—which can be expressed in terms of application qualities of services. Traditional real-time computing systems are a narrow special case whose parameters and core properties are predominately static, and presumed to be known á priori. Those systems have very limited (albeit potentially important) applicability. Many dynamically real-time systems exist, created by application domain experts outside the real-time computing field. These experiences are usually held as proprietary or classified. They usually suffer from the lack of a coherent foundation for real-time per se. The design, implementation, and application of real-time systems (both static and dynamic) can be extended and strengthened by creating such a foundation based on first principles for those core properties. This book introduces one approach to that. Timeliness is dynamically expressive using the time/utility functions and utility accrual paradigm. Uncertainty of timeliness predictability can be reasoned about—beyond what is possible with conventional probability theory—using application-specific instances of mathematical theories of evidence based on belief functions. This foundation has been successfully employed in different real-time contexts having wickedly dynamic parameters and core properties, where traditional static real-time perspectives and traditions were inadequate and counter-productive.
N.B. There still are pages from the previous (c. 2008-2012) version of this site which I have not yet updated and integrated (or removed).