A major obstacle in the technology transfer agenda of behavioral analysis and design methods is the need for logics or automata to express properties for control-intensive systems. Interaction-modeling notations may offer a replacement or a complement, with a practitioner-appealing and lightweight flavor, due partly to the sub specification of intended behavior by means of scenarios. We propose a novel approach consisting of engineering a new formal notation of this sort based on a simple compact declarative semantics: VTS (visual timed event scenarios). Scenarios represent event patterns, graphically depicting conditions over traces. They predicate general system events and provide features to describe complex properties not expressible with MSC-like notations. The underlying formalism supports partial orders and real-time constraints. The problem of checking whether a timed-automaton model has a matching trace is proven decidable. On top of this kernel, we introduce a notation to state properties over all system traces: conditional scenarios, allowing engineers to describe uniquely rich connections between antecedent and consequent portions of the scenario. An undecidability result is presented for the general case of the model-checking problem over dense-time domains, to later identify a decidable-yet practically relevant-subclass, where verification is solvable by generating antiscenarios expressed in the VTS-kernel notation.

Formal description of real-time requirements is a difficult and error prone task. Conceptual and tool support for this activity plays a central role in the agenda of technology transference from the formal verification engineering community to the real-time systems development practice. In this article we present VTS, a visual language to define complex event-based requirements such as freshness, bounded response, event correlation, etc. The underlying formalism is based on partial orders and supports real-time constraints. The problem of checking whether a timed automaton model of a system satisfies these sort of scenarios is shown to be decidable. Moreover, we have also developed a tool that translates visually specified scenarios into observer timed automata. The resulting automata can be composed with a model under analysis in order to check satisfaction of the stated scenarios. We show the benefits of applying these ideas to some case studies.

Research in Model-Checking is focused on increasing the size of the problems tools can deal with. The ultimate wave has been the use of Distributed-Computing, where a cluster of computers work together to solve the problem [8, 3, 9].In our work we present a distributed model-checker that evolves from the tool Kronos [5] and can handle backwards computation of TCTL-reachability formulae [1] over timed-automata [2]. Our proposal, including the arguments of its correctness, is based on software architectures, using a notation adapted from [6]. We find such an approach a natural and general way to address the development of complex tools that need to incorporate new features and optimizations as they evolve.We introduce some interesting features such as a priori graph partitioning (using METIS [7], a standard library for graph partitioning), a sophisticated machinery to reach optimum performance (communication piggybacking and delayed messaging) and dead-time utilization, where every processor uses time intervals of inactivity to perform auxiliary, time-consuming tasks that will later speed up the rest of the computation.The correctness proof strategy combines an architecture evolution with the theoretical results about fix point calculation developed by Patrick Cousot in 1978 [4].

We present a general framework for the formal specification and algorithmic analysis of hybrid systems. A hybrid system consists of a discrete program with an analog environment. We model hybrid systems as finite automata equipped with variables that evolve continuously with time according to dynamical laws. For verification purposes, we restrict ourselves to linear hybrid systems, where all variables follow piecewise-linear trajectories. We provide decidability and undecidability results for classes of linear hybrid systems, and we show that standard program-analysis techniques can be adapted to linear hybrid systems. In particular, we consider symbolic model-checking and minimization procedures that are based on the reachability analysis of an infinite state space. The procedures iteratively compute state sets that are definable as unions of convex polyhedra in multidimensional real space. We also present approximation techniques for dealing with systems for which the iterative procedures do not converge.