Combination of Abstractions in the ASTRÉE Static Analyzer

We describe the structure of the abstract domains in the Astrée static analyzer, their modular organization into a hierarchical network, their cooperation to over-approximate the conjunction/reduced product of different abstractions and to ensure termination using collaborative widenings and narrowings. This separation of the abstraction into a combination of cooperative abstract domains makes Astrée extensible, an essential feature to cope with false alarms and ultimately provide sound formal verification of the absence of runtime errors in very large software.