University of Leicester

informatics

Computer Science Seminars and Short Courses

Semester 2, 2009/10

Seminar programme


Seminar details

Towards Building a Knowledge Base for Research on Andean Weaving

Sven Helmer (Birkbeck, University of London)
Fri, July 9, 14:00 in BEN LT2 (Host: Tadeusz Litak, Alexander Kurz)

We are working on a knowledge base to store 3D Andean textile patterns together with rich cultural and historic context information. This will allow ontological studies in museum collections as well as on ethnographic and archaeological fieldwork. We build on an existing ontology, extending it to incorporate more content and make it more accessible. This goes well beyond storing and retrieving textile patterns and enables us to capture the semantics and wider context of these patterns.


Permissive Nominal Logic

Murdoch James Gabbay (Heriot-Watt University)
Fri, June 4, 14:00 in Ben LT2 (Host: Alexander Kurz)

Permissive Nominal Logic(PNL) is an extension of first-order logic where term-formers can bind names in their arguments. This allows for direct axiomatisations with binders, such as the forall-quantifier of first-order logic itself and the lambda-binder of the lambda-calculus. This also allows us to finitely axiomatise arithmetic. Like first- and higher-order logic and unlike other nominal logics, equality reasoning is not necessary to alpha-rename. All this gives PNL much of the expressive power of higher-order logic, but terms, derivations and models of PNL are first-order in character, and the logic seems to strike a good balance between expressivity and simplicity. Using a paper in PPDP'10 as a basis, I will give a tour of PNL. More information can be found on my webpage.


Modelling and Analysis of Quantum Protocols

Rajagopal Nagarajan (University of Warwick)
Fri, May 14, 14:00 in BEN LT2 (Host: Thomas Erlebach)

The novel field of quantum computation and quantum information has gathered significant impetus in the last few years, and it has the potential to radically impact the future of information technology. While the successful construction of a large-scale quantum computer may be some years away, secure communication involving quantum cryptography has already been implemented, and equipment for quantum cryptography is commercially available. The major selling point of quantum cryptography is unconditional security. But can this be guaranteed in practice? Even when protocols have been mathematically proved to be secure, it is notoriously difficult to achieve robust and reliable implementations of secure systems. Techniques based on formal verification are now widely used by industry to ensure that (classical) systems meet their specifications. In this talk, I will give an overview of our ongoing work in using such techniques for the modelling and analysis of quantum protocols and, eventually, their implementations.

(Joint work with Simon Gay and Nick Papanikolaou).


Smart cards in public transport: the Mifare Classic Case

Bart Jacobs (Nijmegen, The Netherlands)
Thu, May 6, 10:00 in BEN LT5 (!!) (Host: Alexander Kurz)

The Mifare Classic chipcard has been dismantled. Between 1 and 2 billion copies have been sold worldwide. The card is mainly used for access to buildings and for public transport. The talk will give an overview of these developments and pay special attention to the OV-chipcard in the Netherlands and to London's Oyster card. Both are broken: data on the card, including balances, can be changed easily.


Transforming XML - the XSLT language

Michael Kay (Saxonica Limited)
Fri, April 30, 14:00 in BEN LT2 (Host: Rajeev Raman)

XSLT is a widely-used language for transforming XML - sometimes into HTML for display on a browser, often into other XML vocabularies. Michael Kay is the editor of the XSLT 2.0 specification, author of a reference book on the language, and developer of Saxon, a leading implementation available in open source and commercial variants. The purpose of the talk is to explore some interesting questions about XSLT:

  • What kind of language is it, and why?
  • What do users like about it? Why did it catch on? How does this relate to the original design goals for the language?
  • What do non-users dislike about it? Would it have been better to make XSLT more procedural?
  • Or to turn that around, what exactly are the benefits that arise because XSLT is declarative and rule-based?
  • How do XSLT and XQuery compare? Why have two languages with such a high level of overlap?
  • Why is there so little academic interest in XSLT compared with XQuery, given that XSLT has ten times the amount of usage?
  • (A question I am often asked:) How come a one-man company can implement new W3C specifications five years ahead of Microsoft, IBM, and Oracle?

The talk should be interesting both to people who know XML and XSLT well, and to those with a more general interest in the factors that influence the design and adoption of programming languages.


Local Algorithms for Robotic Formation Problems

Friedhelm Meyer auf der Heide (Heinz Nixdorf Institute & Computer Science Department, University of Paderborn)
Fri, April 23, 14:00 in KE LT3 (Host: Thomas Erlebach)

Assume a scenario with a set of autonomous mobile robots having initial positions in the plane. Their goal is to move in such a way that they eventually reach a prescribed formation. Such a formation may be a straight line between two given endpoints (short communication chain), a circle or any other geometric pattern, or just one point (gathering problem). In this talk, I consider simple local strategies for such robotic formation problems: the robots are limited to see only robots within a bounded radius; they are memoryless, without common orientation. Thus, their decisions where to move next are solely based on the relative positions of robots within the bounded radius. I will present local strategies for short communication chains and gathering, and present runtime bounds assuming different time models. All previous algorithms with a proven time bound assume global view on the positions of all robots.


Linear-Time Haplotype Inference on Pedigree without Recombinations

Bethany Chan (Hong Kong)
Wed March 31, 10:00 in BEN LT8 (!!) (Host: Stanley Fung)

In diploid organisms, such as humans, chromosomes come in pairs, and experiments often yield genotypes, which blend haplotypes for the chromosome pair. This gives rise to the problem of inferring haplotypes from genotypes. Given a pedigree P and each node associated with a genotype, the Haplotyping Pedigree Data (with no recombinations) Problem (HPD-NR) is to find a consistent haplotype configuration for P such that the haplotypes of each child are Mendelian-consistent, i.e., one of the child's haplotypes is exactly the same as one of its father's and the other is the same as one of its mother's. Li and Jiang formulated the problem as an mn x mn matrix and solved HPD-NR by Gaussian elimination which could be solved in polynomial time (O(m^3n3)), where n is the number of individuals in the pedigree and m is the number of loci for each individual. In this paper, we propose a new algorithm that can either find a CHC solution or report "no solution" in O(mn) time, which is optimal.


Reasoning about multi-core x86 programs

Scott Owens (Cambridge)
Fri 26 March, 14:00 in BEN LT2 (Host: Irek Ulidowski)

With the rise of multi-core processors, shared-memory concurrency has become a widespread feature of computation, from hardware, to operating systems, to programming languages such as C++ and Java. However, none of these provide sequentially consistent views of shared memory; instead they have relaxed memory models, which make concurrent programs even more challenging to understand. Making matters worse, the public vendor architectures, supposedly specifying what programmers can rely on, are often in informal prose, which leads to confusion on exactly what behaviours a processor is allowed to have.

In this talk, I will present a formal model of the x86's relaxed memory architecture from the viewpoint of an assembly language programmer, and I will relate this model to a few versions of the Intel and AMD documentation, highlighting their various ambiguities and unsoundnesses.

The model is based on the insertion of store buffers between each processor and main memory, and so it provides strong guarantees relative to many other relaxed memory architectures. I will briefly discuss an approach to reasoning about low-level concurrency primitives that takes advantage of these guarantees, and its application to examples, including a spin lock taken from the Linux kernel.


Mixing Information and Logic

M. Andrew Moshier (Chapman University, CA, USA)
Fri 19 March, 14:00 in BEN LT2 (Host: Alexander Kurz)

We discuss two ways to mix information (from a domain theoretic point of view) and propositional logic. The first has its roots in Kleene's metamathematical investigations of three-valued logic, where evaluation of propositions may possibly diverge. The second is closely related to Belnap's proposal (of some interest for knowledge-based systems in distributed environments) to consider a four-value logic: true, false, undefined and contradiction. Kleene's system is closely related to domain theory anyway, as divergence is a fundamental notion that is well-modelled in domains. Belnap, on the other hand, explicitly discusses the idea that the four truth values come equipped with two natural lattice orders: logic, in which false and true are the bounds, and a second order which he calls "information," in which undefined is least informative, contradiction is most informative and true and false are incomparible.

In this talk, we will take Belnap's terminology seriously, by allowing for possibly infinitary accumulation of information along the lines of domain theory (and implicit in Kleene's approach). This ties Kleene and Belnap closely together. As a result, we develop two systems that mix logic and information based on three- and four-valued logic. In the end, however, we will show that the two approaches are equivalent. We conclude with a dicussion of logic and information in a more general setting.


A Traceability Attack Against e-Passports

Tom Chothia (Birmingham)
Fri 12 March, 14:00 in BEN LT2 (Host: Alexander Kurz)

I will briefly describe two pieces of work we have been doing at Birmingham, one on analysing traceability attacks in the applied pi-calculus and the other on using information theory to measure information leaks. Then I'll describe a case study involving "e-passports". Since 2004, many nations have started issuing passports that contain an RFID tag that, when powered, broadcast information. It is claimed that these passports are more secure and that our data will be protected from any possible unauthorised attempts to read it. We have shown that there is a flaw in one of the passport's protocols that makes it possible to trace the movements of a particular passport, without having to break the passport's cryptographic key. All an attacker has to do is to record one session between the passport and a legitimate reader, then by replaying a particular message, the attacker can distinguish that passport from any other. We have implemented our attack and tested it successfully against passports issued by a range of nations.


Global Caching for Coalgebraic Description Logics

Dirk Pattinson (Imperial College London)
Fri Feb 26, 14:00 in BEN LT2 (Host: Alexander Kurz)

Coalgebraic description logics offer a common semantic umbrella for extensions of description logics with reasoning principles outside relational semantics, e.g. quantitative uncertainty, non-monotonic conditionals, or coalitional power. Specifically, we work in coalgebraic logic with global assumptions (i.e. a general TBox), nominals, and satisfaction operators, and prove soundness and completeness of an associated tableau algorithm of optimal complexity EXPTIME. The algorithm is based on global caching, which raises hopes of practically feasible implementation. Instantiation of this result to concrete logics yields new algorithms in all cases including standard relational hybrid logic.

This is joint work with Rajeev Gore (ANU), Clemens Kupke (Imperial) and Lutz Schroeder (DFKI Bremen).


Programming Logics for Dynamic Data

Uday Reddy (Birmingham)
Fri Feb 19, 14:00 in ATT LT1 (Host: Jose Fiadeiro)

'Programming logic' refers to logical systems devised by Computer Scientists that allow us to reason about computer programs and prove their properties. The quintessential logic of this kind was devised by Tony Hoare in the 70's for proving properties of simple imperative programs with assignment statements for ordinary variables. The extension of Hoare Logic for dealing with dynamic data, accessed via pointers, was devised by John Reynolds in 2000, and refined by Peter O'Hearn and colleagues. This system is called Separation Logic. Over the last 10 years, the subject has developed rapidly, dealing with data abstraction, concurrency, verification tools and program analysis tools. This talk introduces the logic and explains the rationale behind its basic features.

Reference:

J. C. Reynolds, Separation Logic: A logic for shared mutable data structures. IEEE Symposium on Logic in Computer Science, 2002, pp 55-74. URL: http://www.cs.cmu.edu/~jcr/seplogic.pdf


A closer look at MDD

Pedro Molina (Software Architect at Capgemini Spain)
Fri Feb 12, 14:00 in ATT LT1 (Host: Jose Fiadeiro, Artur Boronat)

Model Driven Development (MDD) is an engineering approach to software development based in models and code generation. The quality and productivity gain is measured in an order of magnitude if compared to traditional development. This talk will introduce to the audience the key concepts of the approach, a review of the current technologies to support it, the context where it can be applied, the economics foundations in terms of ROI and some real usage scenarios.


Meta-Modelling for Language Engineering

Juan de Lara (Universidad Autónoma in Madrid)
Fri Feb 5, 14:00 in ATT LT1 (Host: Reiko Heckel)

Model-Driven Engineering (MDE) is a software engineering paradigm that seeks developing software faster with higher levels of quality. It does so by increasing the level of abstraction at which engineers work, promoting the use of models in contrast to programs. In this way, developers deal with less “accidental” details, as the notations are closer to the application domain. In MDE, models are not only used for documentation, but they are the core asset in the process, being activelly used, e.g. to (re-)generate code, for validation and verification, and for maintenance.

Thus, a crucial aspect of MDE is to design high-level, domain-specifc (visual) languages, appropriate for the domain of interest. The description of such languages is also done through models. This activity is called meta-modelling and will be the topic of the presentation. The presentation will introduce the basic techniques of meta-modelling, giving an overview on how to describe the abstract and concrete syntax of visual languages. We will discuss tools and standards, and end the presentation showing current limitations and trends in current research.


Towards the Maturation of Usability and User Experience Evaluation Methods (U2XEMs)

Effie Law (Leicester)
January 29, 14:00 in ATT LT1 (Host: Jose Fiadeiro)

Recently, the field of usability has been expanded thanks to recent advances in mobile, ubiquitous, social, and tangible computing technologies that have led to a shift (i.e. the Third Wave HCI) towards to an emphasis on user experience (UX), where user’s feelings, motivations, and values are given a lot of attention. Nonetheless, it remains yet unclear how UX should be defined and measured. Researchers and practitioners tend to view UX with the lens of usability, though the scope of the former is broader than that of latter, considering elusive attributes such as affect, emotion, fun, excitement, engagement, empathy, value, to name just a few. Paradoxically, without clearly defining these componential attributes, a range of new UX evaluation methods (UXEMs), which are derived by adapting known usability evaluation methods (UEMs) and by tapping on the imaginative power of proposers, have been thrown out to the wider HCI communities. Apparently, those emerging UXEMs entail further validation and consolidation. This talk aims to present state-of-the-art of the UEM and UXEM development and discuss the related theoretical/practical issues. It comprises three major parts: (1) To address the scoping, strengths and weaknesses of the popular UEMs and UXEMs; (2) To review the definitional issue of User Experience (UX) and various models of UX; (3) To illustrate with concrete case studies which combinations of traditional and emergent usability and UX evaluation methods are deployed in different sectors and to discuss associatedissues as well as outlook for the future research; Examples: 80Days – Evaluation of adaptive digital educational games (DEGs)


Semester 1, 2009/10

Seminar programme


Seminar details

Tony Clark (Thames Valley University)
Nov27, 14:00 in BEN LT2 (Host: Artur Boronat)


Splitting and scheduling jobs in a hybrid flowshop

Jiyin Liu (Business School, Loughborogh University)
Nov 20, 14:00 in BEN LT2 (Host: Shengxiang Yang)

This talk addresses lot streaming problems, which involve both lot sizing and scheduling decisions, in a two-stage hybrid flowshop with m identical machines at the first stage and a single machine at the second stage. The objective is to minimise the production lead times.

We first analyze some special cases of the problem, the single-job problem with given number of sublots and the single-job problem with equal sublot sizes, and provide efficient optimal solutions. The general single-job problem and the multi-job problem are then studied. Heuristic solutions are proposed to solve these problems. Worst-case analysis and computational experiment show that the proposed heuristic algorithms generate close-to-optimal solutions.


Lazy Systematic Unit Testing for Java

Tony Simons (University of Sheffield)
Nov 13, 14:00 in BEN LT2 (Host: Reiko Heckel, Tamim Khan)

Testing from state-based specifications is a proven technique for exercising software components, to check for all expected and unwanted behaviours. However, in the Agile Methods community, there is a resistance even to simple state-based specifications and an over-reliance on manually created regression tests, which fail to find all faults. The "lazy systematic unit testing" method was created in response. It is based on the two notions of "lazy specification", the ability to defer finalising the software's apparent specification until a late stage in development; and "systematic testing", the ability to explore the state-space of a software component exhaustively, to bounded depth.

The approach is exemplified in a Java unit testing tool, JWalk. This infers the apparent specification of compiled Java classes, by a combination of static and dynamic analysis, and limited interaction with the programmer. The tool is able to excercise all method protocols, all algebraic constructions and all high-level state transitions, to bounded depth. Once the oracle for the specification has been acquired, testing is fully automatic. The test sets adapt gracefully when changes are made to the code; and re-generated tests perform significantly better than regression tests. In a testing challenge, a JWalk tester was able to test two orders of magnitude more paths than an expert tester writing manual tests for JUnit.

The talk will include a demonstration of the JWalk tool.


Unification and Narrowing in Maude

Santiago Escobar (Technical University of Valencia)
Mon, Nov 9, 11:00 in BEN LT3 (Host: Artur Boronat)

Maude is a high-performance reflective language and system supporting both equational and rewriting logic specification and programming for a wide range of applications, and has a relatively large worldwide user and open-source developer base. We have recently introduced support for unification and narrowing in Maude 2.4. Unification is supported in Core Maude, the core rewriting engine of Maude, with commands and metalevel functions for order-sorted unification modulo some frequently occurring equational axioms. Narrowing is currently supported in its Full Maude extension. I will give a brief summary of these novel features of Maude 2.4 and talk about some applications.


Evolutionary Multiobjective Optimisation and User Preferences (Slides)

Juergen Branke (Warwick University)
Nov 6, 14:00 in BEN LT2 (Host: Shengxiang Yang)

Many practical optimization problems require the consideration of multiple, conflicting objectives. In such cases, usually no single optimal solution exists. Instead, there is a set of so-called efficient or Pareto-optimal solutions with different trade-offs. In the absence of additional user preference information, they all have to be regarded as equally good.

Evolutionary algorithms, i.e., heuristics inspired by natural evolution, are gaining increasing popularity for such problems. Because they work on a population of solutions, they can be used to search for a well-distributed set of Pareto-optimal solutions in one run, which are then given to the decision maker to choose from. This talk will give an introduction to evolutionary multiobjective optimisation, and then discuss why and how the decision maker’s preferences should be incorporated already during the optimisation, rather than only after optimisation, as currently most evolutionary multiobjective optimisation approaches do.


Graphical Reasoning in Symmetric Monoidal Categories (Slides)

Lucas Dixon (Edinburgh)
Thu, Nov 4, 12:00 in tba (Host: Reiko Heckel, Paolo Torrini)

Symmetric monoidal categories provide a foundational formalism for a variety of important domains, including quantum computation. These categories have a natural visualisation as a form of graphs. I will present a formalism for equational reasoning about such graphs and develop this into a generic proof system with a fixed logical kernel. A salient feature of our system is that it provides a formal and declarative account of derived results that can include 'ellipses'-style notation. I will illustrate the framework by describing the graphical language applied to quantum computation and boolean circuits, and show how this can be used to perform computations symbolically. #


A completeness result for gs-monoidal categories (Slides)

Fabio Gadducci (University of Pisa)
Thu, Nov 5, 10:00 in KE 527 (Host: Emilio Tuosto, Alexander Kurz)

Building on previous results concerning the functorial semantics of partial and multi-algebras, the talk discusses the category of free semi-modules over a semiring (considered as the Kleisli category of the semiring monad). At first, it is proved that such Kleisli category is gs-monoidal (i.e., it is symmetric monoidal and each object has a comonoid structure), whenever the underlying category is cartesian: hence, it represents a suitable semantical domain for multi-algebras. Furthermore, and more important, two arrows of the freely generated gs-monoidal category are shown to be isomorphic iff they are identified by every possible intepretation in the category of free semi-modules for the semiring of natural numbers.


Relations on Graphs and Hypergraphs (Slides)

John Stell (University of Leeds)
Fri Oct 30, 14:00 in BEN LT2 (Host: Reiko Heckel, Paolo Torrini)

The theory of rough sets provides one approach to understanding data at different levels of detail. An equivalence relation on a set can represent a notion of indistinguishability and arbitrary subsets can then be described approximately with respect to this relation. While this is very well-known, the generalization to graphs raises a number of issues such as: what should we mean by a relation on a graph or a hypergraph, and what role do these relations play in describing graphs at multiple levels of detail? Another approach to granularity is provided by mathematical morphology which has applications in image processing, but which, in a sense, subsumes rough set theory. In this talk I will discuss relations on graphs and hypergraphs and their connections with the lattice-theoretic account of mathematical morphology.


Minimal Social Situations (Slides)

Andrew Colman (School of Psychology, University of Leicester)
Fri Oct 23, 14:00 in ATT LT1 (Host: Jose Fiadeiro)

This talk will focus on research not yet published on minimal social situations -- repeated games in which players learn to cooperate without awareness of the payoff structure or even of the involvement of other players in the outcomes. We have used experimental methods to test theoretical predictions about adaptive learning of cooperative responses in minimal social situations of varying group sizes. We have also used Monte Carlo methods, which have suggested that players approach minimal social situations using a noisy version of the win-stay, lose-change decision rule, deviating from the deterministic rule less frequently after rewarding than unrewarding outcomes.


The `Archaeology' of Transformations (Slides)

Yiyun Yu (The Open University)
Fri Oct 16, 14:00 in ATT LT1 (Host: Jose Fiadeiro)

During a software project's lifetime, the software's artefacts and developers go through many transformations: components are added, removed and modified to fix bugs and add new features, people join and leave the project or change their responsibilities, etc. This tutorial looks at some of the challenges faced, techniques developed and findings obtained in reconstructing, measuring and visualising the historical transformations that happen during the evolution of software and developer teams.


Is there always an algorithm? An introduction to computability theory (Slides)

Rick Thomas (University of Leicester)
Fri Oct 9, 14:00 in ATT LT1 (Host: Jose Fiadeiro)

Computability theory is concerned with the following type of question: given a problem, does there exist an algorithm to solve that problem? This is of fundamental importance in computing; there is no point trying to design an algorithm to solve a problem if no such algorithm exists!

In this talk we will give a gentle introduction to computability theory. We will give some idea of the history of the subject, mentioning some of the key figures involved; as we will see, this sort of question preceded the modern computer. We will then give some examples of problems for which no algorithm exists.


Savara - from Art to Engineering: It’s all in the description (Slides)

Steve Ross-Talbot (Cognizant Technology Solutions)
Fri Oct 2, 14:00 in ATT LT1 (Host: Jose Fiadeiro)

If we cannot describe it we cannot understand much less talk about any of its properties. So why is description often the poor man of computational science? What can we do to change it?

In this session we shall present a new open source community project called Savara that focusses on describing distributed systems in terms of the behavior and behavioral typing which leads to a robust and accurate description and yields a better understanding of that that we build.

The purpose of Savara is to develop a new methodology for Enterprise Architecture, called “Testable Architecture”, and provide appropriate tooling support. Savara's initial aim is to support SOA solutions.

In presenting Savara we shall demonstrate how an eClaims system can be designed and implemented from requirements gathering through successive refinement to a solution. Savara is very new but much of what we show here is already in use in both Red Hat and Cognizant Technology Solutions. The tools that we use to demonstrate are freely available as community open source and the example will also be provided.

This methodology aims to ensure that any artifacts defined during the development lifecycle can be validated against other artifacts in preceding and subsequent phases. This ensures that the final delivered system is guaranteed to meet the original business requirements. Through runtime governance, it is also possible to ensure that the running system continues to meet those requirements.

As a system evolves, through subsequent enhancements to the business requirements, having such a precise understanding of the system, from requirements, through design, implementation and deployment, enables more sophisticated change management techniques to be considered.

It is very much a working session so you will be asked, if you have the time, to bring your laptops and download the pi4soa toolsuite from www.pi4soa.org. Enclosed is a little project that forms the basis of the talk. At the start of the talk we shall show you how to load the project and then you can follow or try out things during the session.


Author: Alexander Kurz (kurz mcs le ac uk), T: 0116 252 5356.
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