Formal Specification and Implementation of Priority Queue using Stream Functions

Abstract

Formal specification of software components, as a core research area in software engineering, has been widely studied for decades. Although quite a few formal models have been proposed for this purpose, specification of concrete software components is still a challenging task due to the complexity of the functionalities of the components. In this paper, the authors use the stream function model to specify the behavior of priority queue, a commonly used software component. This specification formally defines the regular behavior and fault tolerance behavior of priority queue. In particular, a priority-concatenation operator is defined to handle the ordering of data items to ensure the highest-priority item is removed first. A finite state machine is built based on this specification as an implementation of priority queue. In addition, the authors also discuss a priority upgrading approach to handle possible starvation situation of low-priority data items in the priority queue.