Modelling Hybrid Systems in Event-B and Hybrid Event-B: A Comparison of Water Tanks
Hybrid and cyberphysical systems pose significant challenges for a formal development formalism based on pure discrete events. This paper compares the capabilities of (conventional) Event-B for modelling such systems with the corresponding capabilities of the Hybrid Event-B formalism, whose design was intended expressly for such systems. We do the comparison in the context of a simple water tank example, in which filling and emptying take place at different rates, necessitating a control strategy to ensure that the safety invariants are maintained. The comparative case study is followed by a general discussion of issues in which the two approaches reveal different strengths and weaknesses. It is seen that restricting to Event-B means handling many more things at the meta level, i.e. by the user, than is the case with its Hybrid counterpart.
KeywordsMode Event Water Tank Safety Property Discrete Transition Continuous Behaviour
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