Data Consistency in Hard Real-Time Systems

The incorporation of database technology into hard real-time systems presents an important but difficult challenge to any system designer. Notions of consistency and failure atomicity are attractive for architects of dependable hard real-time applications. Unfortunately the hard real-time requirements of bounded access times are not easily imposed upon the concurrency control methods usually found in current database models. The model of data consistency presented here uses temporal consistency constraints in order to ensure that data values are sufficiently recent to be usable. Blocking is avoided by imposing the restriction that only one type of transaction can write to a particular data object, and by using a nonblocking access mechanism. Data itself is considered to be either perishable or non-perishable.