Practical Application of Functional and Relational Methods for the Specification and Verification of Safety Critical Software

Lawford, Mark; McDougall, J. L.; Froebel, P.A.; Moum, Greg

doi:10.1007/3-540-45499-3_8

Cited by 17 publications

(7 citation statements)

References 2 publications

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“…In particular, for each table that is syntactically valid, PVS automatically generates its associated healthiness conditions of completeness and disjointness as type correctness conditions (TCCs). Furthermore, we have expertise built from past experience in applying PVS to check requirements and designs in the nuclear domain [8] that gave us confidence in using the toolset. For modelling real-time behaviour, we reused parts of the PVS theories from [5,4] (see Sec.…”

Section: Tabular Expressionsmentioning

confidence: 99%

Formal Verification of Real-Time Function Blocks Using PVS

Pang

Wang

Lawford

et al. 2015

Electron. Proc. Theor. Comput. Sci.

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A critical step towards certifying safety-critical systems is to check their conformance to hard realtime requirements. A promising way to achieve this is by building the systems from pre-verified components and verifying their correctness in a compositional manner. We previously reported a formal approach to verifying function blocks (FBs) using tabular expressions and the PVS proof assistant. By applying our approach to the IEC 61131-3 standard of Programmable Logic Controllers (PLCs), we constructed a repository of precise specification and reusable (proven) theorems of feasibility and correctness for FBs. However, we previously did not apply our approach to verify FBs against timing requirements, since IEC 61131-3 does not define composite FBs built from timers. In this paper, based on our experience in the nuclear domain, we conduct two realistic case studies, consisting of the software requirements and the proposed FB implementations for two subsystems of an industrial control system. The implementations are built from IEC 61131-3 FBs, including the on-delay timer. We find issues during the verification process and suggest solutions.

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Section: Tabular Expressionsmentioning

confidence: 99%

Formal Verification of Real-Time Function Blocks Using PVS

Pang

Wang

Lawford

et al. 2015

Electron. Proc. Theor. Comput. Sci.

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“…The syntactic constructs that we use the most are "if-then-else" predicates and tables, which we will explain as we use them. An example of using tabular expressions to specify and verify the Darlington Nuclear Shutdown System (SDS) in PVS can be found in [13]. PVS has a powerful interactive proof checker to perform sequent-style deductions.…”

Section: Preliminariesmentioning

confidence: 99%

“…Tabular expressions [20,21] are a way to document system requirement that have proven to be both practical and effective in industry [13,25]. PVS [18] is a non-commercial theorem prover, and provides an integrated environment with mechanized support for writing specifications using tabular expressions and (higher-order) predicates, and for (interactively) proving that implementations satisfy the tabular requirements using sequent-style deductions.…”

Section: Introductionmentioning

confidence: 99%

Formalizing and Verifying Function Blocks Using Tabular Expressions and PVS

Pang

Wang

Lawford

et al. 2014

Communications in Computer and Information Science

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Abstract. Many industrial control systems use programmable logic controllers (PLCs) since they provide a highly reliable, off-the-shelf hardware platform. On the programming side, function blocks (FBs) are reusable components provided by the PLC supplier that can be combined to implement the required system behaviour. A higher quality system may be realized if the FBs are pre-certified to be compliant with an international standard such as IEC 61131-3. We present an approach to formalizing FB requirements using tabular expressions, and to verifying the correctness of the FBs implementations in the PVS proof environment. We applied our approach to the example FBs of IEC 61131-3 and identified issues in the standard: ambiguous behavioural descriptions, missing assumptions, and erroneous implementations.

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“…Tolerances were taken into account on the system inputs and outputs where necessary, effectively making the specifications relational. 5 With mathematical requirements in place, it becomes possible to formally verify that the system design meets the requirements as a part of the development process. Figure 2 shows the idealized development process together with the tools used in producing the documentation and software for the Darlington SDS Redesign.…”

Section: Overview Of the Darlington Redesign Projectmentioning

confidence: 99%

Formal Verification of Nuclear Systems: Past, Present, and Future

Lawford¹,

Wassyng²

2012

ISIJ

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In this paper we review the Systematic Design Verification Process used on the computer controlled shutdown systems of the Darlington Nuclear Generating Station Shutdown Systems. The Software Requirements Specification (SRS) made extensive use of tabular expressions to document the requirements as did the Software Design Description (SDD). Systematic Design Verification was then performed based upon the 4-Variable Model to verify that the design was correct with respect to its requirements. Custom tools were developed to process the SRS and SDD documents to produce "block theorems" for the PVS theorem prover that were used to verify the majority of the functional requirements. We discuss how the formal methods were integrated into the forward going software development process and techniques that were used to manage the complexity of the verification task. We offer some lessons learned in the process and discuss the future of formal verification for nuclear systems.

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Practical Application of Functional and Relational Methods for the Specification and Verification of Safety Critical Software

Cited by 17 publications

References 2 publications

Formal Verification of Real-Time Function Blocks Using PVS

Formal Verification of Real-Time Function Blocks Using PVS

Formalizing and Verifying Function Blocks Using Tabular Expressions and PVS

Formal Verification of Nuclear Systems: Past, Present, and Future

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