Weiss, Gera
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Publication On Omega-Languages Defined by Mean-Payoff Conditions(2009-03-01) Alur, Rajeev; Degorre, Aldric; Weiss, Gera; Maler, OdedIn quantitative verification, system states/transitions have associated payoffs, and these are used to associate mean-payoffs with infinite behaviors. In this paper, we propose to define ω-languages via Boolean queries over mean-payoffs. Requirements concerning averages such as “the number of messages lost is negligible” are not ω-regular, but specifiable in our framework. We show that, for closure under intersection, one needs to consider multi-dimensional payoffs. We argue that the acceptance condition needs to examine the set of accumulation points of sequences of mean-payoffs of prefixes, and give a precise characterization of such sets. We propose the class of multi-threshold mean-payoff languages using acceptance conditions that are Boolean combinations of inequalities comparing the minimal or maximal accumulation point along some coordinate with a constant threshold. For this class of languages, we study expressiveness, closure properties, analyzability, and Borel complexity.Publication Ranking Automata and Games for Prioritized Requirements(2008-07-01) Alur, Rajeev; Weiss, Gera; Kanade, AdityaRequirements of reactive systems are usually specified by classifying system executions as desirable and undesirable. To specify prioritized requirements, we propose to associate a rank with each execution. This leads to optimization analogs of verification and synthesis problems in which we compute the "best" requirement that can be satisfied or enforced from a given state. The classical definitions of acceptance criteria for automata can be generalized to ranking conditions. In particular, given a mapping of states to colors, the Büchi ranking condition maps an execution to the highest color visited infinitely often by the execution, and the cyclic ranking condition with cycle k maps an execution to the modulo-k value of the highest color repeating infinitely often. The well-studied parity acceptance condition is a special case of cyclic ranking with cycle 2, and we show that the cyclic ranking condition can specify all ω-regular ranking functions. We show that the classical characterizations of acceptance conditions by fixpoints over sets generalize to characterizations of ranking conditions by fixpoints over an appropriately chosen lattice of coloring functions. This immediately leads to symbolic algorithms for solving verification and synthesis problems. Furthermore, the precise complexity of a decision problem for ranking conditions is no more than the corresponding acceptance version, and in particular, we show how to solve Büchi ranking games in quadratic time.Publication RTComposer: A Framework for Real-Time Components With Scheduling Interfaces(2008-10-01) Alur, Rajeev; Weiss, GeraWe present a framework for component-based design and scheduling of real-time embedded software. Each component has a clearly specified interface that includes the methods used for sensing, computation, and actuation, along with a requirement given as a regular set of macro-schedules. Each macro-schedule is an infinite sequence that specifies, for every time slot, the set of component methods invoked in that slot. The macro-scheduler composes the specifications of all the components, along with the platform specification that constrains which methods can be executed within a single slot, to generate a feasible macro-schedule. Within a slot, we use logical execution time semantics, and this microscheduling is implemented on top of a native priority-based scheduler. With this approach, each component can be specified and analyzed in a platform-independent way, and at the same time, the performance can vary with changing load and changing processing speed. We describe an implementation using Real-Time Java. Scheduling specifications can be given as periodic tasks, or using temporal logic, or as omega-automata. Components can be added dynamically, and non-real-time components are allowed. We demonstrate the benefits of the approach using case studies.Publication Specification and Analysis of Network Resource Requirements of Control Systems(2009-04-01) Weiss, Gera; Fischmeister, Sebastian; Alur, Rajeev; Anand, MadhukarWe focus on control systems in which sensors send data to actuators via a bus shared with other applications. An approach is proposed for specifying and implementing dynamic scheduling policies for the bus with performance guarantees. Specifically, we propose an automata-based scheduler which we automatically generate from a model of the controlled plant and the controller. We show that, in addition to ensuring performance, our approach allows adjustments to dynamic conditions such as varying disturbances and network load.We present a full development path from performance specifications (exponential stability) to a control design and its implementation using Controller Area Network (CAN).Publication Automata Based Interfaces for Control and Scheduling(2007-04-03) Weiss, Gera; Alur, RajeevWe propose the use of formal languages of infinite words over the alphabet of task identifiers as an interface between control designs and software implementations. We argue that this approach is more flexible than the classical real-time scheduling framework based on periodic tasks, and allows composition of interfaces by language-theoretic operations. We show that finite automata over infinite words offer analyzable representation and can capture many interesting interface specifications such as exponential stability of switched linear systems.Publication Modeling and Analysis of Multi-hop Control Networks(2009-04-13) Rajeev, Alur; Pappas, George James; D'Innocenzo, Alessandro; Weiss, Gera; Johansson, Karl HWe propose a mathematical framework, inspired by the Wireless HART specification, for modeling and analyzing multi-hop communication networks. The framework is designed for systems consisting of multiple control loops closed over a multi-hop communication network. We separate control, topology, routing, and scheduling and propose formal syntax and semantics for the dynamics of the composed system. The main technical contribution of the paper is an explicit translation of multi-hop control networks to switched systems. We describe a Mathematica notebook that automates the translation of multihop control networks to switched systems, and use this tool to show how techniques for analysis of switched systems can be used to address control and networking co-design challenges.