http://www.cs.ox.ac.uk/seminars/ All en-gb 360 Tue, 14 Feb 2012 02:11:36 GMT Tue, 14 Feb 2012 02:11:36 GMT All http://blogs.law.harvard.edu/tech/rss/ http://www.cs.ox.ac.uk/seminars/698.html Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-oasis-698 Thu, 05 Jan 2012 11:05:23 GMT http://www.cs.ox.ac.uk/seminars/710.html <br/>Room 105 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-cakes-710 Wed, 25 Jan 2012 03:04:07 GMT http://www.cs.ox.ac.uk/seminars/687.html Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-oasis-687 Tue, 22 Nov 2011 11:27:16 GMT http://www.cs.ox.ac.uk/seminars/667.html <br/>380 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-departmental-667 Fri, 07 Oct 2011 09:19:29 GMT http://www.cs.ox.ac.uk/seminars/718.html <br/>147 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-infsys-718 Sun, 12 Feb 2012 06:29:09 GMT http://www.cs.ox.ac.uk/seminars/706.html <br/>Room 105 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-cakes-706 Tue, 24 Jan 2012 01:55:46 GMT http://www.cs.ox.ac.uk/seminars/697.html <p>&nbsp;</p> <p>To be defined, but should deal with observations on the evolution of a large piece of code.</p> <br/>Room 051 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-Software Engineering at Credit Suisse-697 Wed, 04 Jan 2012 24:20:12 GMT http://www.cs.ox.ac.uk/seminars/696.html <p>Quality assurance in very large information systems is a big challenge. We will talk about testing as a means to assure appropriate quality. Testing practices we will discuss include a multi-stage testing process, separate organizations for testing in order to be more efficient and avoid conflicts of interest, avoiding sensitive data in development and testing and static quality assurance. We will focus on how to test in a large, highly integrated application landscape. Finally, we will discuss testing practices that go beyond functional tests, such as performance, penetration, and destruction tests.</p> <br/>Room 051 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-Software Engineering at Credit Suisse-696 Wed, 04 Jan 2012 24:20:12 GMT http://www.cs.ox.ac.uk/seminars/695.html <p>In this talk, we will make the point that the security of an information system is determined by the weakest link in a long chain of security measures, both technical and organizational. Very often this weakest link is human behavior, while it is very rarely a theoretical weakness in the cryptographic algorithm. We will show, how we focus on holistic design of security measures in order to strengthen the weakest link. Finally, we will discuss the necessary measures to secure financial transactions in the Internet and, becoming more important every day, on mobile devices.</p> <br/>Room 051 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-Software Engineering at Credit Suisse-695 Wed, 04 Jan 2012 24:20:12 GMT http://www.cs.ox.ac.uk/seminars/694.html <p>Depending on the data they store and the processes they support, information systems incur different levels of risk. Credit Suisse categorizes its information systems in a finite number of levels along the three dimensions of availability/maximum data loss, confidentiality and integrity. Each level comes with clear guidelines regarding design, development and testing of the corresponding system. We will show the framework, explain some of the concepts in more detail and analyze how development and operating cost of a system changes when it has to fulfill different standards.</p> <br/>Room 051 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-Software Engineering at Credit Suisse-694 Wed, 04 Jan 2012 24:17:34 GMT http://www.cs.ox.ac.uk/seminars/702.html <p>The aim of the talk is to demonstrate (on figures) the main ideas of the decidability of bisimulation equivalence for first-order grammars. This provides an alternative for Senizergues' decidability proof (1998, 2005) for nondeterministic pushdown automata with deterministic popping epsilon-steps, which generalized his decidability proof for the famous problem of language equivalence of deterministic pushdown automata (1997, 2001). One crucial novelty of the proof presented here is the framework of first-order terms. This framework seems to be more natural for the problem, allowing a presentation which should be transparent for general computer science audience. Though it seems that both the original proof and the proof presented here use the same ideas on an abstract level, the presented (substantially shorter) proof has not arisen as a translation of the original proof, and a detailed comparison would require an enormous technical work. For the deterministic (sub)case, a primitive recursive complexity upper bound was derived by Stirling (2002). Here we also suggest a way of presenting the ideas behind Stirling's proof in the framework of terms.</p> <br/>147 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-infsys-702 Thu, 19 Jan 2012 11:27:52 GMT http://www.cs.ox.ac.uk/seminars/701.html <p>In this talk, I will present our recent results about repairing XML documents satisfying a given restriction schema into&nbsp;XML documents&nbsp;satisfying a given target schema. Specifically, I will focus on the more general question of whether one can get from any tree in a regular language R to some tree in another regular language T with a finite, uniformly bounded, number of edit operations (i.e., deletions and insertions of nodes). I will present an effective characterization of the pairs of specifications R and T for which such a uniform bound exists and show the complexity of the problem under different representations of the regular tree languages (e.g., DTDs, &nbsp;tree automata). Finally, I will point out some connections with the analogous problem for regular languages of words, which was previously studied.</p> <br/>147 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-infsys-701 Thu, 19 Jan 2012 10:12:49 GMT http://www.cs.ox.ac.uk/seminars/717.html <p>Model checking based on Petri net unfoldings is an approach widely applied to cope with the state space explosion problem caused by concurrency. In this talk I will describe a recent condensed representation of a Petri net's behaviour called merged processes, which copes well not only with concurrency, but also with other sources of state space explosion, like sequences of choices and non-safeness. Moreover, this representation is sufficiently similar to the traditional unfoldings, so that a large body of results developed for the latter can be re-used. Experiments indicate that this representation of a Petri net's behaviour alleviates the state space explosion problem to a significant degree and is suitable for model checking.</p> Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-verification-717 Mon, 06 Feb 2012 11:00:02 GMT http://www.cs.ox.ac.uk/seminars/716.html <p>Stochastic modeling and algorithmic verification techniques have been proved useful in analyzing and detecting unusual trends in performance and energy usage of systems such as power management controllers and wireless sensor devices. Many important properties are dependent on the cumulated time that the device spends in certain states, possibly intermittently. We study the problem of verifying continuous-time Markov chains (CTMCs) against linear duration properties (LDP), i.e. properties stated as conjunctions of linear constraints over the total duration of time spent in states that satisfy a given property. We identify two classes of LDP properties, eventuality duration properties (EDP) and invariance duration properties (IDP), respectively referring to the reachability of a set of goal states, within a time bound; and the continuous satisfaction of a duration property over an execution path. The central question that we address is how to compute the probability of the set of infinite timed paths of the CTMC that satisfy a given LDP. We present algorithms to approximate these probabilities up to a given precision, stating their complexity and error bounds. The algorithms mainly employ an adaptation of uniformization and the computation of volumes of multi-dimensional integrals under systems of linear constraints, together with different mechanisms to bound the errors.<br /><br /> This is a rehearsal talk for HSCC12', joint work with Taolue Chen, Marta Kwiatkowska and Alexandru Mereacre.</p> <br/>147 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-verification-716 Fri, 03 Feb 2012 09:54:14 GMT http://www.cs.ox.ac.uk/seminars/712.html <p>We present automatic verification techniques for the modelling and analysis of probabilistic systems that incorporate competitive behaviour. These systems are modelled as turn-based stochastic multi-player games, in which the players can either collaborate or compete in order to achieve a particular goal. We define a temporal logic called rPATL for expressing quantitative properties of stochastic multi-player games. This logic allows us to reason about the collective ability of a set of players to achieve a goal relating to the probability of an event's occurrence or the expected amount of cost/reward accumulated. We give a model checking algorithm for verifying properties expressed in this logic and implement the techniques in a probabilistic model checker, based on the PRISM tool. We demonstrate the applicability and efficiency of our methods by deploying them to analyse and detect potential weaknesses in a variety of large case studies, including algorithms for energy management and collective decision making for autonomous systems.<br /> <br />This is joint work with Taolue Chen, Vojtech Forejt, Marta Kwiatkowska and David Parker.</p> <br/>051 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-verification-712 Thu, 26 Jan 2012 08:33:48 GMT http://www.cs.ox.ac.uk/seminars/703.html <p>Bounded model checking (BMC) is a highly successful bug-finding method that examines paths of bounded length for violations of a given regular or $\omega$-regular specification. A "completeness threshold" for a given model $M$ and specification $\varphi$ is a bound $k$ such that, if no counterexample to $\varphi$ of length $k$ or less can be found in $M$, then $M$ in fact satisfies $\varphi$. The quest for `small' completeness thresholds in BMC goes back to the very inception of the technique, over a decade ago, and remains a topic of active research.<br /><br />For a fixed specification, completeness thresholds are typically expressed in terms of key attributes of the models under consideration, such as their diameter (length of the longest shortest path) and especially their "recurrence diameter" (length of the longest loop-free path). A recent research paper (Kroening et al.) identified a large class of LTL specifications having completeness thresholds "linear" in the models' recurrence diameter. However, the authors left open the question of whether linearity is in general even decidable.<br /><br />In this talk, we settle the problem in the affirmative, by showing that the linearity problem for both regular and $\omega$-regular specifications (provided as automata and B\"uchi automata respectively) is PSPACE-complete. Moreover, we establish the following dichotomies: for regular specifications, completeness thresholds are either linear or exponential, whereas for $\omega$-regular specifications, completeness thresholds are either linear or at least quadratic.</p> <p>This is joint work with Joel Ouaknine and James Worrell.</p> <br/>051 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-verification-703 Fri, 20 Jan 2012 10:27:00 GMT http://www.cs.ox.ac.uk/seminars/691.html <p>This is the part 2 of two related talks on the use of algebra for unifying calculi of programming. In this second part, I will discuss some (slightly) more advanced aspects of the topic.&nbsp; For example, I will explain concrete models of the algebra, such as regular languages, partial order models, relations, and a new tracelet model due to Struth.&nbsp; In passing, if time permits, I will also give algebraic definitions of some useful programming design patterns like contracts and transactions.</p> <br/>051 Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-verification-691 Mon, 28 Nov 2011 10:34:55 GMT http://www.cs.ox.ac.uk/seminars/709.html <br/>Lecture Theatre B (LTB) Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-oasis-709 Wed, 25 Jan 2012 24:31:53 GMT http://www.cs.ox.ac.uk/seminars/708.html <pre>By a fragment of a natural language we mean a subset of that language equipped with a semantics that translates its sentences into some formal system such as first-order logic. The familiar concepts of satisfiability and entailment can be defined for <br />any such fragment in a natural way. The question then arises, for any given fragment of a natural language, as to the computational complexity of determining satisfiability and entailment within that fragment. We present a series of fragments of <br />English whose satisfiability problems range in complexity from NLOGSPACE-complete to r.e.-complete, showing how different combinations of grammatical constructions conspire to yield the observed complexity. <br />We also discuss some proof-theoretical reflexes of these complexity results, in terms of the existence (or non-existence) of syllogism-like systems of inference rules for the fragments in question. Thus, this talk constitutes a study in how to <br />investigate the computational and logical properties of grammatical constructions in natural language.<br /></pre> <br/>Lecture Theatre B (LTB) Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-oasis-708 Wed, 25 Jan 2012 24:25:16 GMT http://www.cs.ox.ac.uk/seminars/713.html <p>We present the PRIME tool which utilizes static specification mining techniques to extract useful specifications of library APIs from a large number of code fragments that use it, and then use the collected samples for code completion, verification, and - by using data mining techniques - to aggregate the samples into use-cases and sort them according to popularity and complexity.</p> <p>Programming is becoming more and more about using frameworks and libraries, with most of them designed to support a wide range of usage scenarios. Typically, a programmer only needs partial functionality from a library, but is required to navigate the extensive library interface (API) to find how to implement the desired functionality. Instead of navigating the complicated library code and documentation, programmers often rely on code examples of client programs that use the library. Such code examples can often be easily obtained from library documentation, other programmers, or via a myriad of search engines and other online tools. Making sense of these vast numbers of examples, however, can be an extremely challenging task. Code fragments using the API of interest may appear in slightly different contexts and are often interleaved with irrelevant code, making it hard for a programmer to tease out the relevant details. Furthermore, for a given code sample there is always the possibility that its use of the API is erroneous or sub-optimal. These factors make it hard for a human to benefit from this vast amount of available information. Using a combination of program analysis and machine learning techniques, PRIME mines library specifications from a large collection of client code using it, allowing programmers to write new code using the library, even when they are not familiar with it. The results from PRIME can then also be used for automatic completion or verification of new code using that API.</p> <br/>Lecture Theatre B Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-departmental-713 Wed, 01 Feb 2012 09:47:46 GMT http://www.cs.ox.ac.uk/seminars/666.html <p>We survey the well-known algebraic laws of sequential programming, and propose some less familiar laws for concurrent programming.&nbsp; On the basis of these laws, we derive the rules of a number of classical programming calculi, for example, those due to&nbsp; Hoare, Milner, Dijkstra, Back, Morgan, Kahn, Plotkin and Jones. The laws are simpler than each of the calculi, and yet stronger than all of them put together. We end with a discussion of the role of unification in Science and Engineering.</p> <p>This is the first part of two related talks. The second part will be presented in the verification seminar on 22 Feb 2012.</p> <br/>Lecture Threatre B Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-departmental-666 Fri, 07 Oct 2011 09:17:43 GMT http://www.cs.ox.ac.uk/seminars/719.html <p>Despite significant advances in programming languages and verification tools, programming <br />remains a tedious, error-prone, and expensive activity.&nbsp; This talk surveys an emerging approach <br />to software design in&nbsp; which a programmer and an automated program-synthesis tool collaborate <br />to generate software that meets its specification.&nbsp; A programmer expresses her insights about the <br />design using synthesis artifacts of different kinds such as programs that may contain ambiguities, <br />declarative specifications of high-level requirements,&nbsp; positive and negative examples of desired <br />behaviors, and optimization criteria for selecting among alternative implementations. <br />The synthesis tool composes these different views about the structure and functionality of the system <br />into a unified&nbsp; concrete implementation using a combination of algorithmic techniques such as decision <br />procedures for constraint-satisfaction problems, iterative schemes for abstraction and refinement, <br />and data-driven learning. We will illustrate this approach using a number of projects, including one <br />at Penn focusing on design of cache coherence protocols from a mix of concrete and symbolic <br />execution scenarios.</p> <br/>Lecture Theatre B Department of Computer Science, University of Oxford SeminarSeries All oucl-seminar-strachey-719 Mon, 13 Feb 2012 10:33:38 GMT