Verifying Correctness of PLC Software during System Evolution using Model Containment Approach

2025-09-06

AI Summary

Verifying functional correctness after PLC software upgrades remains challenging. To address this, this paper proposes a model-inclusion-based verification method: sequential function charts (SFCs) of both legacy and upgraded PLC programs are automatically translated into Petri net models, followed by rigorous inclusion checking via symbolic path equivalence theory. The key contribution is a novel, efficient symbolic path equivalence decision algorithm, enabling the development of a lightweight, custom Petri net inclusion checker. Evaluated on 80 real-world industrial benchmarks from the OSCAT library, the approach demonstrates strong scalability and high precision. Compared to the state-of-the-art tool verifAPS, it achieves an average 3.9× speedup while maintaining soundness and completeness. This significantly enhances the automation level and practical applicability of PLC upgrade verification.

Technology Category

• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories
• Planning, Routing, and Scheduling: Learning for Planning and Scheduling
• Knowledge Representation and Reasoning: Automated Reasoning and Theorem Proving

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• Security and Privacy: Large-scale security measurements

Abstract

Upgradation of Programmable Logic Controller (PLC) software is quite common to accommodate evolving industrial requirements. Verifying the correctness of such upgrades remains a significant challenge. In this paper, we propose a verification-based approach to ensure the correctness of the existing functionality in the upgraded version of a PLC software. The method converts the older and the newer versions of the sequential function chart (SFC) into two Petri net models. We then verify whether one model is contained within another, based on a novel containment checking algorithm grounded in symbolic path equivalence. For this purpose, we have developed a home-grown Petri net-based containment checker. Experimental evaluation on 80 real-world benchmarks from the OSCAT library highlights the scalability and effectiveness of the framework. We have compared our approach with verifAPS, a popular tool used for software upgradation, and observed nearly 4x performance improvement.

Problem

• Verifying correctness of PLC software upgrades during system evolution
• Ensuring existing functionality is preserved in upgraded PLC versions
• Checking model containment between old and new software versions

Innovation

• Model containment approach for PLC verification
• Converts SFC to Petri nets for comparison
• Symbolic path equivalence algorithm for containment checking