Graphical specification and reasoning: Case study generalised railroad crossing

  • Henning Dierks
  • Cheryl Dietz
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 1313)


A benchmark real-time problem, the generalised railroad crossing [9], serves as illustration of a fully graphical approach to the formal development of correct reactive real-time systems. We show how to formally capture requirements with the graphical language Constraint Diagrams [6] and perform graphical refinement steps towards implementable requirements. These requirements correspond directly to PLC-Automata [4], a class of real-time automata suitable to describe the behaviour of Programmable Logic Controllers (PLCs), a hardware widely used in industry in order to control processes. A compilation schema generates runnable PLC-source-code. Optionally; error states can be introduced in the automata to allow checks of correctness of assumptions. While all languages used — except for the PLC-source-code — are visual, their common semantics is formally defined employing Duration Calculus (DC) [20]. Correctness of refinement steps can thus be formally proven. Once established, graphical refinement rules can be used without knowledge of the DC inside. In that way visuality eases application of formal reasoning.


Programmable Logic Controller Graphical Specification Time Automaton Graphical Language State Assertion 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 1997

Authors and Affiliations

  • Henning Dierks
    • 1
  • Cheryl Dietz
    • 1
  1. 1.University of OldenburgGermany

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