@article{4289, abstract = {A worldwide survey of polymorphic molecular markers shows that the human population is genetically homogeneous, in close agreement with evidence from quite different genes and traits.}, author = {Barton, Nicholas H}, issn = {0960-9822}, journal = {Current Biology}, number = {12}, pages = {757 -- 758}, publisher = {Cell Press}, title = {{Population genetics: A new apportionment of human diversity}}, doi = {10.1016/S0960-9822(06)00397-6}, volume = {7}, year = {1997}, } @misc{4290, author = {Barton, Nicholas H}, booktitle = {Genetical Research}, issn = {0016-6723}, number = {2}, pages = {178 -- 180}, publisher = {Cambridge University Press}, title = {{Natural hybridization and evolution}}, volume = {70}, year = {1997}, } @misc{4291, author = {Barton, Nicholas H}, booktitle = {Genetical Research}, issn = {0016-6723}, number = {2}, pages = {180 -- 181}, publisher = {Cambridge University Press}, title = {{The ecological detective: Confronting models with data}}, volume = {70}, year = {1997}, } @inbook{4293, abstract = {Natural populations differ from the simplest models in ways which can significantly affect their evolution. Real populations are rarely all of the same size; the rates of migration into and out of populations vary in space and time; some populations go extinct, and new ones are established, while all populations fluctuate in size. Furthermore, the genetic properties of real species are not like those assumed in simple models. Alleles are exposed to a wide variety of selection mutation rarely creates novel genotypes with each mutation event, generations overlap, and environments vary from place to place. Evolution in a metapopulation can be substantially different from the predictions of single-population models and, indeed, very different from the simplest models of subdivided species.}, author = {Barton, Nicholas H and Whitlock, Michael}, booktitle = {Metapopulation Biology}, editor = {Hanski, Illka and Gilpin, Michael E.}, isbn = {9780123234452}, pages = {183 -- 210}, publisher = {Academic Press}, title = {{The evolution of metapopulations}}, doi = {10.1016/B978-012323445-2/50012-2}, year = {1997}, } @inproceedings{4438, abstract = {In temporal-logic model checking, we verify the correctness of a program with respect to a desired behavior by checking whether a structure that models the program satisfies a temporal-logic formula that specifies the behavior. The model-checking problem for the branching-time temporal logic CTL can be solved in linear running time, and model-checking tools for CTL are used successfully in industrial applications. The development of programs that must meet rigid real-time constraints has brought with it a need for real-time temporal logics that enable quantitative reference to time. Early research on real-time temporal logics uses the discrete domain of the integers to model time. Present research on real-time temporal logics focuses on continuous time and uses the dense domain of the reals to model time. There, model checking becomes significantly more complicated. For example, the model-checking problem for TCTL, a continuous-time extension of the logic CTL, is PSPACE-complete. In this paper we suggest a reduction from TCTL model checking to CTL model checking. The contribution of such a reduction is twofold. Theoretically, while it has long been known that model-checking methods for untimed temporal logics can be extended quite easily to handle discrete time, it was not clear whether and how untimed methods can handle the reset quantifier of TCTL, which resets a realvalued clock. Practically, our reduction enables anyone who has a tool for CTL model checking to use it for TCTL model checking. The TCTL model-checking algorithm that follows from our reduction is in PSPACE, matching the known bound for this problem. In addition, it enjoys the wide distribution of CTL model-checking tools and the extensive and fruitful research efforts and heuristics that have been put into these tools.}, author = {Henzinger, Thomas A and Kupferman, Orna}, booktitle = {Proceedings of the 5th International Workshop on Hybrid and Real-Time Systems}, isbn = {9783540626008}, location = {Grenoble, France}, pages = {48 -- 62}, publisher = {Springer}, title = {{From quantity to quality}}, doi = {10.1007/BFb0014712}, volume = {1201}, year = {1997}, } @inproceedings{4441, abstract = {Rectangular hybrid automata model digital control programs of analog plant environments. We study rectangular hybrid automata where the plant state evolves continuously in real-numbered time, and the controller samples the plant state and changes the control state discretely, only at the integer points in time. We prove that rectangular hybrid automata have finite bisimilarity quotients when all control transitions happen at integer times, even if the constraints on the derivatives of the variables vary between control states. This is sharply in contrast with the conventional model where control transitions may happen at any real time, and already the reachability problem is undecidable. Based on the finite bisimilarity quotients, we give an exponential algorithm for the symbolic sampling-controller synthesis of rectangular automata. We show our algorithm to be optimal by proving the problem to be EXPTIME-hard. We also show that rectangular automata form a maximal class of systems for which the sampling-controller synthesis problem can be solved algorithmically.}, author = {Henzinger, Thomas A and Kopke, Peter}, booktitle = {Proceedings of the 24th International Colloquium on Automata, Languages and Programming}, isbn = {9783540631651}, location = {Bologna, Italy}, pages = {582 -- 593}, publisher = {Springer}, title = {{Discrete-time control for rectangular hybrid automata}}, doi = {10.1007/3-540-63165-8_213}, volume = {1256}, year = {1997}, } @article{4493, abstract = {A hybrid system is a dynamical system whose behavior exhibits both discrete and continuous change. A hybrid automaton is a mathematical model for hybrid systems, which combines, in a single formalism, automaton transitions for capturing discrete change with differential equations for capturing continuous change. HyTech is a symbolic model checker for linear hybrid automata, a subclass of hybrid automata that can be analyzed automatically by computing with polyhedral state sets. A key feature of HyTech is its ability to perform parametric analysis, i.e., to determine the values of design parameters for which a linear hybrid automaton satisfies a temporal-logic requirement.}, author = {Henzinger, Thomas A and Ho, Pei and Wong Toi, Howard}, issn = {1433-2779}, journal = {Software Tools For Technology Transfer}, number = {1-2}, pages = {110 -- 122}, publisher = {Springer}, title = {{HyTech: A model checker for hybrid systems}}, doi = {10.1007/s100090050008}, volume = {1}, year = {1997}, } @inproceedings{4494, abstract = {A hybrid system consists of a collection of digital programs that interact with each other and with an analog environment. Examples of hybrid systems include medical equipment, manufacturing controllers, automotive controllers, and robots. The formal analysis of the mixed digital-analog nature of these systems requires a model that incorporates the discrete behavior of computer programs with the continuous behavior of environment variables, such as temperature and pressure. Hybrid automata capture both types of behavior by combining finite automata with differential inclusions (i.e. differential inequalities). HyTech is a symbolic model checker for linear hybrid automata, an expressive, yet automatically analyzable, subclass of hybrid automata. A key feature of HyTech is its ability to perform parametric analysis, i.e. to determine the values of design parameters for which a linear hybrid automaton satisfies a temporal requirement.}, author = {Henzinger, Thomas A and Ho, Pei and Wong Toi, Howard}, isbn = {9783540631668}, location = {Haifa, Israel}, pages = {460 -- 463}, publisher = {Springer}, title = {{HyTech: A model checker for hybrid systems}}, doi = {10.1007/3-540-63166-6_48}, volume = {1254}, year = {1997}, } @inproceedings{4496, abstract = {The simulation preorder for labeled transition systems is defined locally as a game that relates states with their immediate successor states. Liveness assumptions about transition systems are typically modeled using fairness constraints. Existing notions of simulation for fair transition systems, however, are not local, and as a result, many appealing properties of the simulation preorder are lost. We extend the local definition of simulation to account for fairness: system S fairly simulates system I iff in the simulation game, there is a strategy that matches with each fair computation of I a fair computation of S. Our definition enjoys a fully abstract semantics and has a logical characterization: S fairly simulates I iff every fair computation tree embedded in the unrolling of I can be embedded also in the unrolling of S or, equivalently, iff every Fair-AFMC formula satisfied by I is satisfied also by S (AFMC is the universal fragment of the alternation-free -calculus). The locality of the definition leads us to a polynomial-time algorithm for checking fair simulation for finite-state systems with weak and strong fairness constraints. Finally, fair simulation implies fair trace-containment, and is therefore useful as an efficientlycomputable local criterion for proving linear-time abstraction hierarchies.}, author = {Henzinger, Thomas A and Kupferman, Orna and Rajamani, Sriram}, booktitle = {Proceedings of the 8th International Conference on Concurrency Theory}, isbn = {9783540631415}, location = {Warsaw, Poland}, pages = {273 -- 287}, publisher = {Springer}, title = {{Fair simulation}}, doi = {10.1007/3-540-63141-0_19}, volume = {1243}, year = {1997}, } @inproceedings{4520, abstract = {We define robust timed automata, which are timed automata that accept all trajectories robustly: if a robust timed automaton accepts a trajectory, then it must accept neighboring trajectories also; and if a robust timed automaton rejects a trajectory, then it must reject neighboring trajectories also. We show that the emptiness problem for robust timed automata is still decidable, by modifying the region construction for timed automata. We then show that, like timed automata, robust timed automata cannot be determinized. This result is somewhat unexpected, given that in temporal logic, the removal of realtime equality constraints is known to lead to a decidable theory that is closed under all boolean operations.}, author = {Gupta, Vineet and Henzinger, Thomas A and Jagadeesan, Radha}, booktitle = {Proceedings of the 5th International Workshop on Hybrid and Real-Time Systems}, isbn = {9783540626008}, location = {Grenoble, France}, pages = {331 -- 345}, publisher = {Springer}, title = {{Robust timed automata}}, doi = {10.1007/BFb0014736}, volume = {1201}, year = {1997}, } @inproceedings{4583, abstract = {In a trace-based world, the modular specification, verification, and control of live systems require each module to be receptive; that is, each module must be able to meet its liveness assumptions no matter how the other modules behave. In a real-time world, liveness is automatically present in the form of diverging time. The receptiveness condition, then, translates to the requirement that a module must be able to let time diverge no matter how the environment behaves. We study the receptiveness condition for real-time systems by extending the model of reactive modules to timed and hybrid modules. We define the receptiveness of such a module as the existence of a winning strategy in a game of the module against its environment. By solving the game on region graphs, we present an (optimal) Exptime algorithm for checking the receptiveness of prepositional timed modules. By giving a fixpoint characterization of the game, we present a symbolic procedure for checking the receptiveness of linear hybrid modules. Finally, we present an assume-guarantee principle for reasoning about timed and hybrid modules, and a method for synthesizing receptive controllers of timed and hybrid modules.}, author = {Alur, Rajeev and Henzinger, Thomas A}, booktitle = {8th International Conference on Concurrency Theory}, isbn = {9783540691884}, location = {Warsaw, Poland}, pages = {74 -- 88}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum für Informatik}, title = {{Modularity for timed and hybrid systems}}, doi = {10.1007/3-540-63141-0_6}, volume = {1243}, year = {1997}, } @article{4584, abstract = {This paper introduces, gently but rigorously, the clock approach to real-time programming. We present with mathematical precision, assuming no prerequisites other than familiarity with logical and programming notations, the concepts that are necessary for understanding, writing, and executing clock programs. In keeping with an expository style, all references are clustered in bibliographic remarks at the end of each section. The first appendix presents proof rules for verifying temporal properties of clock programs. The second appendix points to selected literature on formal methods and tools for programming with clocks. In particular, the timed automaton, which is a finite-state machine equipped with clocks, has become a standard paradigm for real-time model checking; it underlies the tools HyTech, Kronos, and Uppaal, which are discussed elsewhere in this volume.}, author = {Alur, Rajeev and Henzinger, Thomas A}, issn = {1433-2779}, journal = {Software Tools For Technology Transfer}, number = {1-2}, pages = {86 -- 109}, publisher = {Springer}, title = {{Real-time system = discrete system + clock variables}}, doi = {10.1007/s100090050007}, volume = {1}, year = {1997}, } @inproceedings{4605, abstract = {A hybrid system is a dynamical system whose behavior exhibits both discrete and continuous change. A hybrid automaton is a mathematical model for hybrid systems, which combines, in a single formalism, automaton transitions for capturing discrete change with differential equations for capturing continuous change. In this survey, we demonstrate symbolic algorithms for the verification of and controller synthesis for linear hybrid automata, a subclass of hybrid automata that can be analyzed automatically}, author = {Alur, Rajeev and Henzinger, Thomas A and Wong Toi, Howard}, booktitle = {Proceedings of the 36th IEEE Conference on Decision and Control}, isbn = {0780341872}, location = {San Diego, CA, USA}, pages = {702 -- 707}, publisher = {IEEE}, title = {{Symbolic analysis of hybrid systems}}, doi = {10.1109/CDC.1997.650717 }, year = {1997}, } @article{4607, abstract = {We present a verification algorithm for duration properties of real-time systems. While simple real-time properties constrain the total elapsed time between events, duration properties constrain the accumulated satisfaction time of state predicates. We formalize the concept of durations by introducing duration measures for timed automata. A duration measure assigns to each finite run of a timed automaton a real number —the duration of the run— which may be the accumulated satisfaction time of a state predicate along the run. Given a timed automaton with a duration measure, an initial and a final state, and an arithmetic constraint, the duration-bounded reachability problem asks if there is a run of the automaton from the initial state to the final state such that the duration of the run satisfies the constraint. Our main result is an (optimal) PSPACE decision procedure for the duration-bounded reachability problem.}, author = {Alur, Rajeev and Courcoubetis, Costas and Henzinger, Thomas A}, issn = {0925-9856}, journal = {Formal Methods in System Design}, number = {2}, pages = {137 -- 156}, publisher = {Springer}, title = {{Computing accumulated delays in real-time systems}}, doi = {10.1023/A:1008626013578}, volume = {11}, year = {1997}, } @inproceedings{4608, abstract = {State space explosion is a fundamental obstacle in formal verification of designs and protocols. Several techniques for combating this problem have emerged in the past few years, among which two are significant: partial-order reductions and symbolic state space search. In asynchronous systems, interleavings of independent concurrent events are equivalent, and only a representative interleaving needs to be explored to verify local properties. Partial-order methods exploit this redundancy and visit only a subset of the reachable states. Symbolic techniques, on the other hand, capture the transition relation of a system and the set of reachable states as boolean functions. In many cases, these functions can be represented compactly using binary decision diagrams (BDDs). Traditionally, the two techniques have been practiced by two different schools—partial-order methods with enumerative depth-first search for the analysis of asynchronous network protocols, and symbolic breadth-first search for the analysis of synchronous hardware designs. We combine both approaches and develop a method for using partial-order reduction techniques in symbolic BDD-based invariant checking. We present theoretical results to prove the correctness of the method, and experimental results to demonstrate its efficacy.}, author = {Alur, Rajeev and Brayton, Robert and Henzinger, Thomas A and Qadeer, Shaz and Rajamani, Sriram}, booktitle = {9th International Conference on Computer Aided Verification}, isbn = {9783540631668}, location = {Haifa, Israel}, pages = {340 -- 351}, publisher = {Springer}, title = {{Partial-order reduction in symbolic state-space exploration}}, doi = {10.1007/3-540-63166-6_34}, volume = {1254}, year = {1997}, } @inproceedings{4609, abstract = {Temporal logic comes in two varieties: linear-time temporal logic assumes implicit universal quantification over all paths that are generated by system moves; branching-time temporal logic allows explicit existential and universal quantification over all paths. We introduce a third, more general variety of temporal logic: alternating-time temporal logic offers selective quantification over those paths that are possible outcomes of games, such as the game in which the system and the environment alternate moves. While linear-time and branching-time logics are natural specification languages for closed systems, alternating-time logics are natural specification languages for open systems. For example, by preceding the temporal operator “eventually” with a selective path quantifier, we can specify that in the game between the system and the environment, the system has a strategy to reach a certain state. Also the problems of receptiveness, realizability, and controllability can be formulated as model-checking problems for alternating-time formulas}, author = {Alur, Rajeev and Henzinger, Thomas A and Kupferman, Orna}, booktitle = {Proceedings of the 38th Annual Symposium on Foundations of Computer Science}, issn = {0004-5411}, location = {Washington, DC, United States}, pages = {100 -- 109}, publisher = {Association for Computing Machinery (ACM)}, title = {{Alternating-time temporal logic}}, doi = {10.1145/585265.585270}, year = {1997}, }