Abstract Interpretation for Logical Clocks - pdf
Funding: Subject to competition for scholarship 2021
Starting date: from September 1st, 2021
The concrete semantics of programs formalizes the set of all possible executions of a program in all possible environments. In most cases, this set of possible executions is infinite and is not computable. Abstract interpretation consists in considering an abstract semantics, that is a superset of the concrete program semantics . A invariant is a property that holds on all the executions and an abstract domain is a computer representation of a given category of invariants. Our work focuses on the definition of sound models to describe the temporal behavior of programs. We rely on a set of mostly independent logical clocks  to characterize the valid and invalid behaviors of reactive systems . Clocks evolve independently of each other, and not necessarily at regular rates, unless otherwise constrained. We use the Clock Constraint Specification Language (CCSL ) to specify both synchronous and asynchronous constraints and build so-called polychronous specifications . Each CCSL constraint defines a set, usually infinite, of possible behaviors. The expected global behavior of the reactive system is the intersection of all sets of behaviors of all the constraints. The problem of scheduling a CCSL specification, is to, given a finite set of constraints, tell whether or not the intersection of all behaviors of all constraints is empty. If not empty, then the challenge is to represent at least some, possibly all, the valid behaviors so that their properties can be further studied. While it is acceptable to get only an under-approximation of valid schedules, we cannot afford to produce an over-approximation. As such, CCSL constraints can be considered as temporal invariants over the system behavior, and families of constraints may be characterized by abstract domains. Abstract Interpretation has been studied in the context of temporal calculi and logics  and in the particular context of embedded critical software . However, a purely linear or even branching-time model of time `a-la-CTL is not entirely satisfactory to capture the polychronous nature of logical clocks and clock constraints seem to describe different kinds of abstract domains.
The goal of the thesis is study the use of abstract interpretation in the context of logical clock specifications. While CCSL should give a first minimal setting for clock constraints, the overall scope may go beyond CCSL and extend to more general synchronous and asynchronous constraints such as found in synchronous languages . The objective is to get both an adequate abstraction to get a simple-enough computer representation of polychronous specifications, but also to get, as a side effect, possibly efficient analysis verification tools to schedule multi-clock specifications . In particular, we would like to customize a generic constraint solver based on abstract domains  and compare to state-of-the-art solutions relying on industrial SMT solvers  or ad-hoc solvers . It should bring a more general framework to analyze logical specifications and pinpoint some particularly interesting behaviours like periodic schedules  or bad paths .
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- PhD in Computer Sciences: 36 months
Requirements and application
- Hold a Master in Computer Sciences
- Send CV, mark sheets and motivation letter to Frederic.Mallet@univ-cotedazur.fr