The department's research is directed to the foundations of computational models, processes and structures, and the way they support the engineering of software intensive systems. Specific areas of interest are:

Algebraic and Categorical Structures and Methods

Algorithm Design, Analysis and Engineering

Computational Complexity of Algebraic Structures

Deduction, Rewriting and Transformation

Interaction Design and Evaluation of Socio-technical Systems

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Recent Submissions

Detecting and Refactoring Operational Smells within the Domain Name System

The Domain Name System (DNS) is one of the most important components of the Internet infrastructure. DNS relies on a delegation-based architecture, where resolution of names to their IP addresses requires resolving the names of the servers responsible for those names. The recursive structures of the inter dependencies that exist between name servers associated with each zone are called dependency graphs. System administrators' operational decisions have far reaching effects on the DNSs qualit...

Radwan, Marwan; Heckel, Reiko

The Rabin index of parity games

We study the descriptive complexity of parity games by taking into account the coloring of their game graphs whilst ignoring their ownership structure. Colored game graphs are identified if they determine the same winning regions and strategies, for all ownership structures of nodes. The Rabin index of a parity game is the minimum of the maximal color taken over all equivalent coloring functions. We show that deciding whether the Rabin index is at least k is in PTIME for k=1 but NP-hard for a...

Huth, M; Kuo, JHP; Piterman, N

Obligation Blackwell Games and p-Automata

We recently introduced p-automata, automata that read discrete-time Markov chains. We used turn-based stochastic parity games to define acceptance of Markov chains by a subclass of p-automata. Definition of acceptance required a cumbersome and complicated reduction to a series of turn-based stochastic parity games. The reduction could not support acceptance by general p-automata, which was left undefined as there was no notion of games that supported it.
Here we generalize two-player gam...

Piterman, Nir; Chatterjee, Krishnendu

Fatal Attractors in Parity Games: Building Blocks for Partial Solvers

Attractors in parity games are a technical device for solving "alternating" reachability of given node sets. A well known solver of parity games - Zielonka's algorithm - uses such attractor computations recursively. We here propose new forms of attractors that are monotone in that they are aware of specific static patterns of colors encountered in reaching a given node set in alternating fashion. Then we demonstrate how these new forms of attractors can be embedded within greatest fixed-point...

Huth, M.; Kuo, J. H. P.; Piterman, Nir

Modeling and reasoning over distributed systems using aspect-oriented graph grammars

Aspect-orientation is a relatively new paradigm that introduces abstractions to modularize the implementation of system-wide policies. It is based on a composition operation, called aspect weaving, that implicitly modifies a base system by performing related changes within the system modules. Aspect-oriented graph grammars (AOGG) extend the classic graph grammar formalism by defining aspects as sets of rule-based modifications over a base graph grammar. Despite the advantages of aspect-orient...

Machado, Rodrigo; Heckel, Reiko; Ribeiro, Leila

Towards an embedding of Graph Transformation in Intuitionistic Linear Logic

Linear logics have been shown to be able to embed both rewriting-based approaches and process calculi in a single, declarative framework. In this paper we are exploring the embedding of double-pushout graph transformations into quantified linear logic, leading to a Curry-Howard style isomorphism between graphs and transformations on one hand, formulas and proof terms on the other. With linear implication representing rules and reachability of graphs, and the tensor modelling parallel composit...

Torrini, Paolo; Heckel, Reiko

From nondeterministic Buchi and Streett automata to deterministic parity automata

In this paper we revisit Safra's determinization constructions. We show how to construct deterministic automata with fewer states and, most importantly, parity acceptance conditions. Specifically, starting from a nondeterministic Buchi automaton with n states our construction yields a deterministic parity automaton with n2n+2 states and index 2n (instead of a Rabin automaton with (12)nn2n states and n pairs). Starting from a nondeterministic Streett automaton with n states and k pairs our con...

Piterman, Nir

Cell-cycle regulation of NOTCH signaling during C. elegans vulval development.

C. elegans vulval development is one of the best-characterized systems to study cell fate specification during organogenesis. The detailed knowledge of the signaling pathways determining vulval precursor cell (VPC) fates permitted us to create a computational model based on the antagonistic interactions between the epidermal growth factor receptor (EGFR)/RAS/MAPK and the NOTCH pathways that specify the primary and secondary fates, respectively. A key notion of our model is called bounded asyn...

We consider the offline sorting buffer problem. The input is a sequence of items of different types. All items must be processed one by one by a server. The server is equipped with a random-access buffer of limited capacity which can be used to rearrange items. The problem is to design a scheduling strategy that decides upon the order in which items from the buffer are sent to the server. Each type change incurs unit cost, and thus, the cost minimizing objective is to minimize the total numbe...

Chan, Ho-Leung; Megow, Nicole; Stee, Rob van; Sitters, Rene

Improved Practical Compact Dynamic Tries

We consider the problem of implementing a dynamic trie with an emphasis on good practical performance. For a trie with n nodes with an alphabet of size σ, the information-theoretic lower bound is nlogσ+O(n) bits. The Bonsai data structure [1] supports trie operations in O(1) expected time (based on assumptions about the behaviour of hash functions). While its practical speed performance is excellent, its space usage of (1+ϵ)n(logσ+O(loglogn)) bits, where ϵ is any constant >0, is not asymptoti...

Poyias, Andreas; Raman, Rajeev

The infinitary lambda calculus of the infinite eta Böhm trees

In this paper, we introduce a strong form of eta reduction called etabang that we use to construct a confluent and normalising infinitary lambda calculus, of which the normal forms correspond to Barendregt's infinite eta Böhm trees. This new infinitary perspective on the set of infinite eta Böhm trees allows us to prove that the set of infinite eta Böhm trees is a model of the lambda calculus. The model is of interest because it has the same local structure as Scott's D∞-models, i.e. two fini...

Severi, Paula; de Vries, Fer-Jan

Visualising Software as a Particle System

Current metrics-based approaches to visualise un-
familiar software systems face two key limitations: (1) They
are limited in terms of the number of dimensions that can
be projected, and (2) they use fixed layout algorithms where
the resulting positions of entities can be vulnerable to mis-
interpretation. In this paper we show how computer games
technology can be used to address these problems. We present
the PhysVis software exploration system, where software metrics
can be variably...

Scarle, Simon; Walkinshaw, Neil

A Calculus of Mobility and Communication for Ubiquitous Computing

Ubiquitous computing makes various computing devices available throughout the
physical setting. Ubiquitous computing devices are distributed and could be mobile,
and interactions among them are concurrent and often depend on the location of
the devices. Process calculi are formal models of concurrent and mobile systems.
The work in this thesis is inspired by the calculus of Mobile Ambients and other
process calculi such as Calculus of Communicating Systems which have proved to
be succes...

Gul, Nosheen

Groups, formal language theory and decidability

The first four chapters provide an introduction, background information and a
summary of results from some of the relevant literature. In these chapters a proof
is provided if the author was unable to find either a proof or the result itself stated
in the literature.
Chapter 5 focuses on syntactic monoids of languages, it introduces some background
material from the literature and then proves some characterisations of
monoids based on properties that the full preimage of certain subsets...

Jones, Sam Anthony Mark

A Forward Analysis for Recurrent Sets

Non-termination of structured imperative programs is primarily due to infinite loops. An important class of non-terminating loop behaviors can be characterized using the notion of recurrent sets. A recurrent set is a set of states from which execution of the loop cannot or might not escape. Existing analyses that infer recurrent sets to our knowledge rely on one of: the combination of forward and backward analyses, quantifier elimination, or SMT-solvers. We propose a purely forward abstract i...

Bakhirkin, Alexey; Berdine, J.; Piterman, Nir

Reducing Idle Listening during Data Collection in Wireless Sensor Networks

Data collection is one of the predominant operations in wireless sensor networks. This paper focuses on the problem of efficient data collection in a setting where some nodes may not possess data each time data is collected. In that case, idle listening slots may occur, which lead to a waste of energy and an increase in latency. To alleviate these problems, successive-slot schedules were proposed by Zhao and Tang (Infocom 2011). In this paper, we introduce a so-called extra-bit technique to r...

Rasul, Aram; Erlebach, Thomas

Mobile learning in a human geography field course

This paper reports on reusable mobile digital learning resources designed to assist human geography undergraduate students in exploring the geographies of life in Dublin. Developing active learning that goes beyond data collection to encourage observation and thinking in the field is important. Achieving this in the context of large class sizes presents several challenges. Combining in-situ learning with spatially-accurate historical and contemporary multimedia, we developed a set of location...

The Price of Anarchy for Selfish Ring Routing is Two

We analyze the network congestion game with atomic players, asymmetric strategies, and the maximum latency among all players as social cost. This important social cost function is much less understood than the average latency. We show that the price of anarchy is at most two, when the network is a ring and the link latencies are linear. Our bound is tight. This is the first sharp bound for the maximum latency objective.

SIGACT news online algorithms column 24: 2014 so far

In this column, I will discuss some recent papers in online algorithms. It is pleasing to see there
were a number of papers about online algorithms in the top conferences this year. If I have missed
your paper and you want to write about it or about any other topic in online algorithms, don't
hesitate to contact me!

van Stee, Rob

Better Algorithms for Online Bin Stretching

Online Bin Stretching is a semi-online variant of bin packing in which the algorithm has to use the same number of bins as the optimal packing, but is allowed to slightly
overpack the bins. The goal is to minimize the amount of overpacking, i.e., the maximum
size packed into any bin.
We give an algorithm for Online Bin Stretching with a stretching factor of 1:5 for
any number of bins. We also show a specialized algorithm for three bins with a stretching
factor of 11=8 = 1:375.

Böhm, Martin; Sgall, Jin; Stee, Rob van; Veselý, Pavel