Introducing B-Sequenced Petri Nets as a CPN Sub-class for Safe Train Control

Formalizing system specification has been highly valuable in demonstrating safety and consistence of safety critical systems. It is undoubtedly the case in railway signalling, especially the European Rail Traffic Management System/European Train Control System (ERTMS/ETCS). However, the complexity of the European standard specification, especially for its highest level, namely level 3, requires a significant overtake in early modelling approaches when it comes to clearly expressing system functionalities along with safety requirements, all towards a concrete safe design. In this regard, our research introduces a Colored Petri net (CPN) sub-class associated to an Event-B machine and annotated by mathematical sequences, which are ex-pressed in the B-language, all in the view of enriching the modelling techniques intended for system formal specification and verification. In this paper, we show through a detailed ERTMS L3 case study, how such featured CPNs fit in the progressive formalization and verification of Movement Authority (MA) computation.