Requirement-Dependent Extra Invariant Patterns in Deductive Verification of PoST Programs

When developing safety-critical software, in particular software for control systems, formal verification methods which make it possible to prove that the program satisfy the requirements for all execution paths play an important role. One of these methods is deductive verification, in which requirements are formalized in the form of logical formulas, and then verification conditions are generated and proved for the program. One of the promising approaches to the development of control programs is process-oriented programming. Previously, for the deductive verification of process-oriented programs, a method was developed in which requirements are specified in the form of invariants of the control loop statements that should be true between iterations. However, to prove the verification conditions, it is necessary to use information about the program structure, which is usually not contained in the requirements. Therefore, an extra invariant containing such information is also specified. Generating loop invariants is a difficult task to automate. In this paper, it is proposed to use patterns to determine an extra invariant of the control loop. For previously defined classes of requirements described by patterns, in this paper we have defined extra invariant patterns. The proposed approach to determining invariants in combination with previously developed strategies for proving verification conditions makes it possible to make deductive verification of process-oriented programs more automated.