The Use of Formal Methods for Signalling Interfaces

Application of Formal Methods and Interface Standardization in Railway Signalling Systems

The video explores the use of formal methods and interface standardization within railway signalling systems, focusing on the European UIC-led initiative called UNISIG (referred to as “you links” in subtitles). It highlights key technological concepts, product features, and methodologies aimed at improving system development, quality, and interoperability.

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Standardization of Signalling Interfaces

European infrastructure managers collaborate to standardize interfaces between signalling subsystems supplied by different vendors. This approach:

• Reduces lifecycle costs
• Shortens time to market
• Avoids repetitive development efforts

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Reference Architecture

UNISIG has developed a reference architecture that:

• Defines subsystem functions and their interactions
• Places the interlocking system at the core
• Specifies interfaces between the interlocking and field elements such as points, signals, and level crossings

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Complexity and Requirements

Modern signalling systems face increasing complexity due to:

• Rapidly evolving technology
• Growing variations in subsystems
• Stringent requirements for reliability, safety, maintenance, and legal compliance

Interface standardization focuses on use cases that reflect the functional distribution across subsystems, without harmonizing operational rules.

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Lifecycle Model (V Model)

Development follows the European standard V model, which ensures:

• All requirements are systematically addressed
• Phases of specification and integration are covered
• Key areas such as route protection, train protection, and control technology are included

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Model-Based Systems Engineering (MBSE)

UNISIG employs MBSE using SysML to integrate signalling and system engineering expertise:

• Infrastructure managers define use cases
• Use cases are converted into standardized SysML diagrams
• Diagrams represent various model views, including:
  • Technical context
  • Use cases
  • Sequence diagrams
  • State machines

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Virtual Prototyping and Simulation

Executable SysML state machines are used to create virtual prototypes that:

• Simulate and verify subsystem behavior early in development
• Reduce ambiguous text-based requirements
• Minimize design errors
• Lower lifecycle costs through automated verification and validation

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Formal Methods and Mathematical Proofs

To complement system testing, formal methods are applied to mathematically prove that interface specifications meet all requirements:

• Two universities developed a formal modeling language and toolset
• These tools analyze system design quality and compliance with national and UNISIG standards
• Formal verification involves:
  • Translating SysML models into formal models
  • Verifying completeness and correctness
  • Testing compliance with specifications

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Benefits and Future Outlook

The combined use of formal methods and MBSE:

• Improves system comprehensibility
• Facilitates communication among stakeholders
• Enhances quality assurance

This approach is considered essential for the next generation of signalling engineers and will be disseminated through academic publications.

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Guides, Tutorials, and Reviews Provided

• Explanation of the lifecycle V model for railway system development
• Overview of using SysML diagrams for modelling signalling subsystems
• Description of virtual prototyping for simulation and verification
• Introduction to formal methods for mathematical proof of system correctness

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Main Speakers and Sources

• European infrastructure managers involved in UNISIG
• UNISIG representatives developing reference architecture and MBSE approaches
• Two universities collaborating on formal modeling languages and toolsets for formal verification