DSpace Community:
http://hdl.handle.net/2381/316
2015-10-10T10:53:02Z
2015-10-10T10:53:02Z
Detecting and Refactoring Operational Smells within the Domain Name System
Radwan, Marwan
Heckel, Reiko
http://hdl.handle.net/2381/33171
2015-10-03T02:10:10Z
2015-10-02T09:47:21Z
Title: Detecting and Refactoring Operational Smells within the Domain Name System
Authors: Radwan, Marwan; Heckel, Reiko
Abstract: 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 qualities. They need to be soundly made to create a balance between the availability, security and resilience of the system. We utilize dependency graphs to identify, detect and catalogue operational bad smells. Our method deals with smells on a high-level of abstraction using a consistent taxonomy and reusable vocabulary, defined by a DNS Operational Model. The method will be used to build a diagnostic advisory tool that will detect configuration changes that might decrease the robustness or security posture of domain names before they become into production.
Description: In Proceedings GaM 2015, arXiv:1504.02448
2015-10-02T09:47:21Z
The Rabin index of parity games
Huth, M
Kuo, JHP
Piterman, N
http://hdl.handle.net/2381/33162
2015-10-02T02:00:51Z
2015-10-01T15:23:39Z
Title: The Rabin index of parity games
Authors: Huth, M; Kuo, JHP; Piterman, N
Abstract: 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 all fixed k > 1. We present an EXPTIME algorithm that computes the Rabin index by simplifying its input coloring function. When replacing simple cycle with cycle detection in that algorithm, its output over-approximates the Rabin index in polynomial time. Experimental results show that this approximation yields good values in practice.
Description: In Proceedings GandALF 2013, arXiv:1307.4162
2015-10-01T15:23:39Z
Obligation Blackwell Games and p-Automata
Piterman, Nir
Chatterjee, Krishnendu
http://hdl.handle.net/2381/33160
2015-10-02T02:00:49Z
2015-10-01T15:17:15Z
Title: Obligation Blackwell Games and p-Automata
Authors: Piterman, Nir; Chatterjee, Krishnendu
Abstract: 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 games by adding a structural acceptance condition called obligations. Obligations are orthogonal to the linear winning conditions that define winning. Obligations are a declaration that player 0 can achieve a certain value from a configuration. If the obligation is met, the value of that configuration for player 0 is 1.
One cannot define value in obligation games by the standard mechanism of considering the measure of winning paths on a Markov chain and taking the supremum of the infimum of all strategies. Mainly because obligations need definition even for Markov chains and the nature of obligations has the flavor of an infinite nesting of supremum and infimum operators. We define value via a reduction to turn-based games similar to Martin's proof of determinacy of Blackwell games with Borel objectives. Based on this definition, we show that games are determined. We show that for Markov chains with Borel objectives and obligations, and finite turn-based stochastic parity games with obligations there exists an alternative and simpler characterization of the value function. Based on this simpler definition we give an exponential time algorithm to analyze finite turn-based stochastic parity games with obligations. Finally, we show that obligation games provide the necessary framework for reasoning about p-automata and that they generalize the previous definition.
2015-10-01T15:17:15Z
Fatal Attractors in Parity Games: Building Blocks for Partial Solvers
Huth, M.
Kuo, J. H. P.
Piterman, Nir
http://hdl.handle.net/2381/33159
2015-10-02T02:00:50Z
2015-10-01T15:12:37Z
Title: Fatal Attractors in Parity Games: Building Blocks for Partial Solvers
Authors: Huth, M.; Kuo, J. H. P.; Piterman, Nir
Abstract: 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 computations to design solvers of parity games that run in polynomial time but are partial in that they may not decide the winning status of all nodes in the input game. Experimental results show that our partial solvers completely solve benchmarks that were constructed to challenge existing full solvers. Our partial solvers also have encouraging run times in practice. For one partial solver we prove that its run-time is at most cubic in the number of nodes in the parity game, that its output game is independent of the order in which monotone attractors are computed, and that it solves all Buechi games and weak games. We then define and study a transformation that converts partial solvers into more precise partial solvers, and we prove that this transformation is sound under very reasonable conditions on the input partial solvers. Noting that one of our partial solvers meets these conditions, we apply its transformation on 1.6 million randomly generated games and so experimentally validate that the transformation can be very effective in increasing the precision of partial solvers.
2015-10-01T15:12:37Z
Modeling and reasoning over distributed systems using aspect-oriented graph grammars
Machado, Rodrigo
Heckel, Reiko
Ribeiro, Leila
http://hdl.handle.net/2381/33145
2015-10-02T02:00:52Z
2015-10-01T11:02:25Z
Title: Modeling and reasoning over distributed systems using aspect-oriented graph grammars
Authors: Machado, Rodrigo; Heckel, Reiko; Ribeiro, Leila
Abstract: 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-oriented concepts regarding modularity, the implicit nature of the aspect weaving operation may also introduce issues when reasoning about the system behavior. Since in AOGGs aspect weaving is characterized by means of rule-based rewriting, we can overcome these problems by using known analysis techniques from the graph transformation literature to study aspect composition. In this paper, we present a case study of a distributed client-server system with global policies, modeled as an aspect-oriented graph grammar, and discuss how to use the AGG tool to identify potential conflicts in aspect weaving.
2015-10-01T11:02:25Z
Towards an embedding of Graph Transformation in Intuitionistic Linear Logic
Torrini, Paolo
Heckel, Reiko
http://hdl.handle.net/2381/33144
2015-10-02T02:00:52Z
2015-10-01T10:46:22Z
Title: Towards an embedding of Graph Transformation in Intuitionistic Linear Logic
Authors: Torrini, Paolo; Heckel, Reiko
Abstract: 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 composition of graphs and transformations, we obtain a language able to encode graph transformation systems and their computations as well as reason about their properties.
2015-10-01T10:46:22Z
From nondeterministic Buchi and Streett automata to deterministic parity automata
Piterman, Nir
http://hdl.handle.net/2381/33113
2015-09-29T02:00:43Z
2015-09-28T10:47:34Z
Title: From nondeterministic Buchi and Streett automata to deterministic parity automata
Authors: Piterman, Nir
Abstract: 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 construction yields a deterministic parity automaton with nn(k+2)+2(k+1)2n(K+1) states and index 2n(k+1) (instead of a Rabin automaton with (12)n(k+1)n n(k+2)(k+1)2n(k+1) states and n(k+1) pairs). The parity condition is much simpler than the Rabin condition. In applications such as solving games and emptiness of tree automata handling the Rabin condition involves an additional multiplier of n2n!(or(n(k+1))2(n(k+1))! in the case of Streett) which is saved using our construction.
2015-09-28T10:47:34Z
Cell-cycle regulation of NOTCH signaling during C. elegans vulval development.
Nusser-Stein, Stefanie
Beyer, Antje
Rimann, Ivo
Adamczyk, Magdalene
Piterman, Nir
Hajnal, Alex
Fisher, Jasmin
http://hdl.handle.net/2381/33107
2015-09-26T02:00:42Z
2015-09-25T15:22:42Z
Title: Cell-cycle regulation of NOTCH signaling during C. elegans vulval development.
Authors: Nusser-Stein, Stefanie; Beyer, Antje; Rimann, Ivo; Adamczyk, Magdalene; Piterman, Nir; Hajnal, Alex; Fisher, Jasmin
Abstract: 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 asynchrony, which predicts that a limited degree of asynchrony in the progression of the VPCs is necessary to break their equivalence. While searching for a molecular mechanism underlying bounded asynchrony, we discovered that the termination of NOTCH signaling is tightly linked to cell-cycle progression. When single VPCs were arrested in the G1 phase, intracellular NOTCH failed to be degraded, resulting in a mixed primary/secondary cell fate. Moreover, the G1 cyclins CYD-1 and CYE-1 stabilize NOTCH, while the G2 cyclin CYB-3 promotes NOTCH degradation. Our findings reveal a synchronization mechanism that coordinates NOTCH signaling with cell-cycle progression and thus permits the formation of a stable cell fate pattern.
2015-09-25T15:22:42Z
The Sorting Buffer Problem is NP-hard
Chan, Ho-Leung
Megow, Nicole
Stee, Rob van
Sitters, Rene
http://hdl.handle.net/2381/33106
2015-09-26T02:00:40Z
2015-09-25T15:14:43Z
Title: The Sorting Buffer Problem is NP-hard
Authors: Chan, Ho-Leung; Megow, Nicole; Stee, Rob van; Sitters, Rene
Abstract: 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 number of type changes for serving the entire sequence. This problem is motivated by various applications in manufacturing processes and computer science, and it has attracted significant attention in the last few years. The main focus has been on online competitive algorithms. Surprisingly little is known on the basic offline problem. In this paper, we show that the sorting buffer problem with uniform cost is NP-hard and, thus, close one of the most fundamental questions for the offline problem. On the positive side, we give an O(1)-approximation algorithm when the scheduler is given a buffer only slightly larger than double the original size. We also give a dynamic programming algorithm for the special case of buffer size two that solves the problem exactly in linear time, improving on the standard DP which runs in cubic time.
2015-09-25T15:14:43Z
Improved Practical Compact Dynamic Tries
Poyias, Andreas
Raman, Rajeev
http://hdl.handle.net/2381/33033
2015-09-11T02:00:34Z
2015-09-10T08:36:15Z
Title: Improved Practical Compact Dynamic Tries
Authors: Poyias, Andreas; Raman, Rajeev
Abstract: 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 asymptotically optimal. We propose an alternative, m-Bonsai, that uses (1+ϵ)n(logσ+O(1)) bits in expectation, and supports operations in O(1) expected time (again based on assumptions about the behaviour of hash functions). We give a heuristic implementation of m-Bonsai which uses considerably less memory and is slightly faster than the original Bonsai.
2015-09-10T08:36:15Z
The infinitary lambda calculus of the infinite eta Böhm trees
Severi, Paula
de Vries, Fer-Jan
http://hdl.handle.net/2381/32973
2015-08-25T02:00:47Z
2015-08-24T14:09:28Z
Title: The infinitary lambda calculus of the infinite eta Böhm trees
Authors: Severi, Paula; de Vries, Fer-Jan
Abstract: 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 finite lambda terms are equal in the infinite eta Böhm model if and only if they have the same interpretation in Scott's D∞-models.
2015-08-24T14:09:28Z
Visualising Software as a Particle System
Scarle, Simon
Walkinshaw, Neil
http://hdl.handle.net/2381/32949
2015-08-25T01:45:09Z
2015-08-18T10:08:10Z
Title: Visualising Software as a Particle System
Authors: Scarle, Simon; Walkinshaw, Neil
Abstract: 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 mapped to parameters of a physical model and
displayed via a particle system. Entities can be imbued with
attributes such as mass, gravity, and (for relationships) strength
or springiness, alongside traditional attributes such as position,
colour and size. The resulting visualisation is a dynamic scene;
the relative positions of entities are not determined by a fixed
layout algorithm, but by intuitive physical notions such as gravity,
mass, and drag. The implementation is openly available, and we
evaluate it on a selection of visualisation tasks for two openly-
available software systems.
2015-08-18T10:08:10Z
A Calculus of Mobility and Communication for Ubiquitous Computing
Gul, Nosheen
http://hdl.handle.net/2381/32898
2015-08-06T02:01:47Z
2015-08-05T14:17:23Z
Title: A Calculus of Mobility and Communication for Ubiquitous Computing
Authors: Gul, Nosheen
Abstract: 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 successful in the modelling of mobility, communication and structure of systems.
We start by developing operational semantics for the calculus of Mobile Ambients
and Push and Pull Ambient Calculus, and prove that the semantics are sound and
complete with respect to the corresponding underlying reduction semantics. This
thesis proposes a Calculus of Communication and Mobility, denoted by CMCPCA,
for the modelling of mobility, communication and context awareness in the setting
of ubiquitous computing. CMCPCA is an ambient calculus with the in and out
capabilities of Cardelli and Gordon as well the push and pull capabilities of Phillips
and Vigliotti. CMCPCA has a new form of global communication similar to that in
Milner’s CCS. We define a new notion of behavioural equivalence for our calculus
in terms of an observation predicate and action transitions. Thus, we define barbed
bisimulation and congruence, and capability barbed bisimulation and congruence.
We then prove that capability barbed congruence coincides with barbed congruence.
We also include in the calculus a new form of context awareness mechanism that
allows ambients to query their current location and surrounding. We then propose
reduction semantics and operational semantics for the context awareness primitives,
and show that the semantics coincide. Several case studies and a variety of small
examples show the expressiveness and usefulness of our calculus.
2015-08-05T14:17:23Z
Groups, formal language theory and decidability
Jones, Sam Anthony Mark
http://hdl.handle.net/2381/32520
2015-07-09T02:01:09Z
2015-07-08T14:01:15Z
Title: Groups, formal language theory and decidability
Authors: Jones, Sam Anthony Mark
Abstract: 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 satisfy when
considered as a formal language over the generating set.
In Chapter 6 we examine some natural properties of formal languages which are
necessary conditions for a formal language to be a word problem of a group.
We look at which subsets of these conditions are sufficient for a formal language
satisfying them to be a word problem.
Chapter 7 focuses on decision problems. We generalise a theorem of Hartmanis
and Hopcroft and use it to settle the decidability for various language classes of
the conditions from Chapter 6.
Chapter 8 contains a brief exposition of some related areas. We first characterise
the co-word problem for groups and then examine a way of constructing groups
by intersecting their word problems. We conclude this chapter by proving some
simple results about the context-free subset membership problem for groups.
Finally, Chapter 9 contains a brief discussion of possible directions in which one
could extend the work in this thesis. The results in chapters 5, 6 and 7 are to be considered original unless stated
otherwise. Many of the results in chapter 7 have been published in [24]. Many of
the results of chapter 6 have been submitted for publication.
2015-07-08T14:01:15Z
A Forward Analysis for Recurrent Sets
Bakhirkin, Alexey
Berdine, J.
Piterman, Nir
http://hdl.handle.net/2381/32409
2015-09-17T08:54:29Z
2015-06-23T10:23:14Z
Title: A Forward Analysis for Recurrent Sets
Authors: Bakhirkin, Alexey; Berdine, J.; Piterman, Nir
Abstract: 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 interpretation–based analysis that can be used together with a possibly complicated abstract domain where none of the above is readily available. The analysis searches for a recurrent set of every individual loop in a program by building a graph of abstract states and analyzing it in a novel way. The graph is searched for a witness of a recurrent set that takes the form of what we call a recurrent component which is somewhat similar to the notion of an end component in a Markov decision process.
2015-06-23T10:23:14Z
Reducing Idle Listening during Data Collection in Wireless Sensor Networks
Rasul, Aram
Erlebach, Thomas
http://hdl.handle.net/2381/32370
2015-06-13T02:00:43Z
2015-06-12T09:26:08Z
Title: Reducing Idle Listening during Data Collection in Wireless Sensor Networks
Authors: Rasul, Aram; Erlebach, Thomas
Abstract: 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 reduce idle listening further. Each packet includes an extra bit that informs the receiver whether further data packets will follow or not. The extra-bit technique leads to significantly reduced idle listening and improved latency in many cases. We prove that every successive-slot schedule is also an extra-bit schedule. We then consider the special case of linear networks and prove that the optimal length of a successive-slot schedule (or extra-bit schedule) is 4N - 6 time slots, where N ≥ 3 is the number of nodes excluding the sink. Then the proposed extra-bit technique is compared with the successive-slot technique with respect to the expected amount of idle listening, and it is shown that the extra-bit technique reduces idle listening substantially.
Description: timestamp: Thu, 05 Mar 2015 11:05:43 +0100 biburl: http://dblp.uni-trier.de/rec/bib/conf/msn/RasulE14 bibsource: dblp computer science bibliography, http://dblp.org
2015-06-12T09:26:08Z
Mobile learning in a human geography field course
Jarvis, Claire
Tate, Nicholas
Dickie, Jennifer
Brown, Gavin
http://hdl.handle.net/2381/32345
2015-06-04T02:00:18Z
2015-06-03T09:03:12Z
Title: Mobile learning in a human geography field course
Authors: Jarvis, Claire; Tate, Nicholas; Dickie, Jennifer; Brown, Gavin
Editors: Mitchell, J.
Abstract: 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-aware digital mobile tools or ‘mediascapes’. We explore how scaffolding can be achieved in such a context, focusing on the development of students’ observational, enquiry and thinking skills in the field.
2015-06-03T09:03:12Z
The Price of Anarchy for Selfish Ring Routing is Two
Chen, Xujin
Doerr, Benjamin
Doerr, Carola
Hu, Xiaodong
Ma, Weidong
van Stee, Rob
http://hdl.handle.net/2381/32326
2015-06-01T14:54:05Z
2015-06-01T14:53:47Z
Title: The Price of Anarchy for Selfish Ring Routing is Two
Authors: Chen, Xujin; Doerr, Benjamin; Doerr, Carola; Hu, Xiaodong; Ma, Weidong; van Stee, Rob
Abstract: 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.
Description: © ACM, 2014. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in ACM Transactions on Economics and Computation archive
Volume 2 Issue 2, June 2014 http://doi.acm.org/10.1145/2548545
2015-06-01T14:53:47Z
SIGACT news online algorithms column 24: 2014 so far
van Stee, Rob
http://hdl.handle.net/2381/32323
2015-06-01T10:56:07Z
2015-06-01T10:55:27Z
Title: SIGACT news online algorithms column 24: 2014 so far
Authors: van Stee, Rob
Abstract: 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!
2015-06-01T10:55:27Z
Better Algorithms for Online Bin Stretching
Böhm, Martin
Sgall, Jin
Stee, Rob van
Veselý, Pavel
http://hdl.handle.net/2381/32322
2015-06-01T10:44:37Z
2015-06-01T10:31:30Z
Title: Better Algorithms for Online Bin Stretching
Authors: Böhm, Martin; Sgall, Jin; Stee, Rob van; Veselý, Pavel
Abstract: 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.
Description: The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-319-18263-6_3
2015-06-01T10:31:30Z
The optimal absolute ratio for online bin packing
Balogh, Janos
Békési, Jozsef
Dósa, Gyorgy
Sgall, Jiri
Stee, Rob van
http://hdl.handle.net/2381/32320
2015-06-01T09:53:41Z
2015-06-01T09:53:03Z
Title: The optimal absolute ratio for online bin packing
Authors: Balogh, Janos; Békési, Jozsef; Dósa, Gyorgy; Sgall, Jiri; Stee, Rob van
Abstract: We present an online bin packing algorithm with absolute competitive ratio 5/3, which is optimal.
2015-06-01T09:53:03Z
Synthesising Executable Gene Regulatory Networks from Single-Cell Gene Expression Data
Fisher, J.
Köksal, A. S.
Piterman, Nir
Woodhouse, S.
http://hdl.handle.net/2381/32306
2015-08-20T11:57:21Z
2015-05-26T11:29:52Z
Title: Synthesising Executable Gene Regulatory Networks from Single-Cell Gene Expression Data
Authors: Fisher, J.; Köksal, A. S.; Piterman, Nir; Woodhouse, S.
Abstract: Recent experimental advances in biology allow researchers to obtain gene expression profiles at single-cell resolution over hundreds, or even thousands of cells at once. These single-cell measurements provide snapshots of the states of the cells that make up a tissue, instead of the population-level averages provided by conventional high-throughput experiments. This new data therefore provides an exciting opportunity for computational modelling. In this paper we introduce the idea of viewing single-cell gene expression profiles as states of an asynchronous Boolean network, and frame model inference as the problem of reconstructing a Boolean network from its state space. We then give a scalable algorithm to solve this synthesis problem. We apply our technique to both simulated and real data. We first apply our technique to data simulated from a well established model of common myeloid progenitor differentiation. We show that our technique is able to recover the original Boolean network rules. We then apply our technique to a large dataset taken dur- ing embryonic development containing thousands of cell measurements. Our technique synthesises matching Boolean networks, and analysis of these models yields new predictions about blood development which our experimental collaborators were able to verify.
2015-05-26T11:29:52Z
The Description Logic SHIQ with a Flexible Meta-modelling Hierarchy
Severi, Paula G.
Motz, Regina
Rohrer, Edelweis
http://hdl.handle.net/2381/32284
2015-08-20T14:09:52Z
2015-05-19T10:58:05Z
Title: The Description Logic SHIQ with a Flexible Meta-modelling Hierarchy
Authors: Severi, Paula G.; Motz, Regina; Rohrer, Edelweis
Abstract: This work is motivated by a real-world case study where it is necessary to integrate and relate existing ontologies through meta-modelling. For this, we introduce the Description Logic SHIQM which is obtained from SHIQ byadding statements that equate individuals to concepts in a knowledge base. In this new extension, concepts can be individuals of another concept (called meta-concept) which itself can be an individual of yet another concept (called meta meta-concept ) and so on. We define an algorithm that checks consistency of SHIQM by modifying the Tableau algorithm for SHIQ. From the practical point of view, this has the advantage that we can reuse the code of existing OWL reasoners. From the theoretical point of view, it has a similar advantage of reuse. We make use of the existing results and proofs that lead to correctness of the algorithm for SHIQ in order to prove correctness of the algorithm for SHIQM.
2015-05-19T10:58:05Z
Performance and energy evaluation of RESTful web services in Raspberry Pi
Nunes, L. H.
Nakamura, L. H. V.
De F. Vieira, H..
De O. Libardi, R. M.
De Oliveira, E. M.
Estrella, J. C.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32267
2015-05-14T02:00:24Z
2015-05-13T10:06:24Z
Title: Performance and energy evaluation of RESTful web services in Raspberry Pi
Authors: Nunes, L. H.; Nakamura, L. H. V.; De F. Vieira, H..; De O. Libardi, R. M.; De Oliveira, E. M.; Estrella, J. C.; Reiff-Marganiec, Stephan
Abstract: Green computing has emerged as a hot topic leading to a need to understand energy consumption of computations. This need also extends to devices with limited resources as are common in the internet of things. RESTful services have shown their potential on such devices, but there are many choices of frameworks for their development and execution. Current research has analysed performance of the frameworks but no attention has been given to systematically studying their power consumption. In this paper we analyse the execution behaviour and power consumption of web services on devices with limited resources and make initial observations that should influence future development of web service frameworks. Specifically, we conduct experiments comparing web services in the Axis2 and CXF frameworks analysing the respective performance and power consumption. Bringing together the best features of small devices and SoC, it is possible to provide diverse, mobile and green applications - however careful selection of development environments can make significant differences in performance and energy consumption.
2015-05-13T10:06:24Z
Observing access control policies using scrabble games
Ahmad, S.
Abidin, S. Z. Z.
Omar, N.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32266
2015-05-14T02:00:26Z
2015-05-13T09:55:17Z
Title: Observing access control policies using scrabble games
Authors: Ahmad, S.; Abidin, S. Z. Z.; Omar, N.; Reiff-Marganiec, Stephan
Abstract: Access control is concerned with the policies that manage data sharing activities. Access control plays a crucial role in application areas such as education, health and business. However, most programming languages and programming environments do not naturally provide support for implementing access control policies requiring access control policies for systems to be coded as part of the development effort. Access control management policies are high-level features so having to involve a computer programmer during deployment stages for making changes to policies is costly. In this paper, we present an abstraction of access control management policies in the form of extended scrabble in its rules. The needs of access control policies program construct for supporting this game are examined. New relevant program constructs are then incorporated into JACIE (Java-based Authoring language for Collaborative Interactive Environments). The usefulness of these program construct are being demonstrated through the extended scrabble.
2015-05-13T09:55:17Z
Classifying Smart Objects using capabilities
Pérez Hernández, Marco E.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32265
2015-05-14T02:00:22Z
2015-05-13T09:46:00Z
Title: Classifying Smart Objects using capabilities
Authors: Pérez Hernández, Marco E.; Reiff-Marganiec, Stephan
Abstract: The Internet Of Things has emerged, providing an umbrella for the increasing number of heterogeneous Smart Objects that are becoming part of our daily activities. In this scenario, classification approaches are useful to understand differences and identify opportunities of generalization and common solutions, especially when different disciplines are coming together and bringing their individual terms and concepts. We propose a novel model for classifying Smart Objects using capabilities. This five-level model, inspired in the Capability Maturity Models, aims to be simple and inclusive, separating objects with basic capabilities from those with complex ones. In addition, examples of objects for each level are provided as validation of the proposal. The model is useful to identify requirements that Smart Objects have to cover externally as they cannot themselves support them and thus it allows for clear understanding of the external support system (or Middleware) into which the smart object is embedded.
2015-05-13T09:46:00Z
Design and implementation of fault tolerance techniques to improve QoS in SOA
Oliveira, E. M.
Estrella, J. C.
Kuehne, B. T.
Filho, D. M. L.
Adami, L. J.
Nunes, L. H.
Nakamura, L. H.
Libardi, R. M.
Souza, P. S. L.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32264
2015-05-14T02:00:22Z
2015-05-13T09:23:28Z
Title: Design and implementation of fault tolerance techniques to improve QoS in SOA
Authors: Oliveira, E. M.; Estrella, J. C.; Kuehne, B. T.; Filho, D. M. L.; Adami, L. J.; Nunes, L. H.; Nakamura, L. H.; Libardi, R. M.; Souza, P. S. L.; Reiff-Marganiec, Stephan
Abstract: Fault tolerance techniques can improve the trust of users in service oriented architectures as they can ensure data availability. This paper presents an implementation of a novel fault tolerance mechanism in a SOA architecture which simultaneously provides increased availability and better quality of service. In addition to this mechanism, a service selector using reputation ratings of the architecture components is discussed. The selection is based on information from past transactions of the components of the architecture, which allows to identify the best web services able to meet the requests of customers. The mechanisms are tested and a performance evaluation is presented to validate the results.
2015-05-13T09:23:28Z
A semantic approach for efficient and customized management of IaaS resources
Nakamura, L. H. V.
Estrella, J. C.
Santana, R. H. C.
Santana, M. J.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32263
2015-05-14T02:00:24Z
2015-05-13T09:15:14Z
Title: A semantic approach for efficient and customized management of IaaS resources
Authors: Nakamura, L. H. V.; Estrella, J. C.; Santana, R. H. C.; Santana, M. J.; Reiff-Marganiec, Stephan
Abstract: This paper presents a semantic approach to custom management of IaaS (Infrastructure as a Service) resources in a cloud computing environment requiring minimal human intervention from both the cloud provider and the user. The proposal differs from other approaches by using autonomic computing and semantic web techniques together to provide a self-configuring and self-optimizing environment that aims to satisfy SLAs (Service Level Agreements). The approach monitors the virtualized resources to guarantee a customized and optimized use based on financial criteria and energy consumption policies.
2015-05-13T09:15:14Z
Managing access control policy from end user perspective in collaborative environment
Ahmad, S.
Omar, N.
Abidin, S. Z. Z.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32252
2015-05-09T02:04:07Z
2015-05-08T14:55:00Z
Title: Managing access control policy from end user perspective in collaborative environment
Authors: Ahmad, S.; Omar, N.; Abidin, S. Z. Z.; Reiff-Marganiec, Stephan
Abstract: Currently, collaborative environments offer unlimited data sharing for users. Data owners are poorly involved in handling their data for such environment when it deals with data policy. Normally, data access control policy consists of a resource and authorization descriptions which are assigned by the administrator. It is the responsibility of the administrator to set and specify the policy for application services. The policy details are massive and complex for administrator to handle where most of the times there will be cases of unreview services. This paper proposes a framework that allows data owners to provision policies for storing and managing their shared data with third parties. By adapting RBAC model and adding owner's interest on permissions for data operations and objects, the proposed framework will facilitate data access control whereby owners have the freedom to set their own data access policy.
2015-05-08T14:55:00Z
HIAWSC: An Immune Algorithm Based Heuristic Web Service Composition Framework
Xu, J.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32251
2015-09-04T01:45:07Z
2015-05-08T14:39:51Z
Title: HIAWSC: An Immune Algorithm Based Heuristic Web Service Composition Framework
Authors: Xu, J.; Reiff-Marganiec, Stephan
Abstract: The introduction of of web services has led to web service composition being a focus of many researchers. Composing web services using workflows is seen as the most realistic method from an industrial viewpoint. Amongst other method, the use of natural computing methods has been proposed previously to automate web service composition. The need for a fast response when computing the most suitable sequence of services is addressed in this paper. In particular, we propose a novel heuristic immune algorithm with an efficient encoding and mutation method. The algorithm involves two steps: an immune selection operation, which is maintaining antibody population diversity and the clonal selection. The use of a vaccine during the evolution provides heuristic information that accelerates the convergence. Our experimental results illustrate that the proposed heuristic immune algorithm is very effective in improving the convergence speed. We also provide a schema analysis for this method.
2015-05-08T14:39:51Z
Performance Evaluation in a Cloud with the Provisioning of Different Resources Configurations
Batista, B. G.
Estrella, J. C.
Santana, M. J.
Santana, R. H. C.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32250
2015-05-09T02:03:54Z
2015-05-08T14:11:44Z
Title: Performance Evaluation in a Cloud with the Provisioning of Different Resources Configurations
Authors: Batista, B. G.; Estrella, J. C.; Santana, M. J.; Santana, R. H. C.; Reiff-Marganiec, Stephan
Abstract: Cloud computing is a computing style where resource providers can offer on-demand services in a transparent way and clients usually pay as they go. It introduces a new level of flexibility and scalability for IT users addressing challenges such as the rapid change in IT and the need to reduce cost and time of infrastructure management. However, to be able to offer QoS guarantees without limiting the number of accepted requests, providers must be able to dynamically adjust the available resources to serve requests. This dynamic resource management is not a trivial task, bringing its own challenges related to workload and performance modelling, and deployment and monitoring of applications on virtualised IT resources. An efficient mapping between resources and applications ensures workload balancing and good resource utilization and allows to meet the QoS levels required by clients. This paper presents a performance evaluation that considers different resource configurations in a cloud environment to define which dimension of resource scaling has real impact on client applications.
2015-05-08T14:11:44Z
Low-Latency Service Data Aggregation Using Policy Obligations
Reiff-Marganiec, Stephan
Tilly, M.
Janicke, H.
http://hdl.handle.net/2381/32249
2015-05-09T02:04:03Z
2015-05-08T13:59:21Z
Title: Low-Latency Service Data Aggregation Using Policy Obligations
Authors: Reiff-Marganiec, Stephan; Tilly, M.; Janicke, H.
Abstract: The Internet of Things, large scale sensor networks or even in social media, are now well established and their use is growing daily. Usage scenarios in these fields highlight the requirement to process, procure, and provide information with almost zero latency. This work is introducing new concepts for enabling fast communication by limiting information flow through filtering concepts combined with data processing techniques adopted from complex event processing. Specifically we introduce a novel mediation services architecture using filter policies to reduce latency. The filter policies define when and what data services need to provide to the mediator and thus save on bandwidth. The filter policies describe temporal conditions between two events removing the need to keep a complete history while still allowing temporal reasoning. Promising experimental results highlight the advantages to be gained from the approach.
2015-05-08T13:59:21Z
PEESOS: A Web Tool for Planning and Execution of Experiments in Service Oriented Systems
Nunes, L. H.
Vasconcelos Nakamura, L. H.
Tardiole Kuehne, B.
De Oliveira, E. M.
De O Libardi, R. M.
Junqueira Adami, L.
Estrella, J. C.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32241
2015-09-15T09:34:26Z
2015-05-08T10:56:39Z
Title: PEESOS: A Web Tool for Planning and Execution of Experiments in Service Oriented Systems
Authors: Nunes, L. H.; Vasconcelos Nakamura, L. H.; Tardiole Kuehne, B.; De Oliveira, E. M.; De O Libardi, R. M.; Junqueira Adami, L.; Estrella, J. C.; Reiff-Marganiec, Stephan
Abstract: Performing functionality testing in service-oriented architectures is not a trivial task. The difficulty is especially the large number of components that may be present in a SOA such as brokers, providers, service registries, clients, monitoring tools, data storage tools, etc. Thus, in order to facilitate the process of conducting functional testing and capacity planning in service-oriented systems, we present PEESOS. This first version is a functional prototype that offers facilities to assist researchers and industry to test their new applications, allowing collaborations that can be done between the participants to achieve an appropriate objective when developing a new application. The first results show that it is possible to make a planning environment easier to operate and to readily obtain results for performance evaluation of a target architecture. Since this is a first version of the prototype, it has interface and scalability limitations as well as needing improvements in performance of the logs repository and also in a core engine. We hope that such limitations can be corrected in the near future, including gathering information from the scientific community to make the prototype a useful and accessible tool. PEESOS is on-line and available at http://peesos.wsarch.lasdpc.icmc.usp.br.
Description: PEESOS is on-line and available at http://peesos.wsarch.lasdpc.icmc.usp.br.
2015-05-08T10:56:39Z
Providing Quality of Service on Services Selection Using Anycast Techniques
Adami, L. J.
Estrella, J. C.
De Oliveira, E. M.
Reiff- Marganiec, Stephan
http://hdl.handle.net/2381/32239
2015-05-09T02:03:40Z
2015-05-08T10:48:38Z
Title: Providing Quality of Service on Services Selection Using Anycast Techniques
Authors: Adami, L. J.; Estrella, J. C.; De Oliveira, E. M.; Reiff- Marganiec, Stephan
Abstract: Over the last years, the complexity and variety of services available on the Internet increased. This fact is leading to the search for efficient techniques of routing client requests to the best server available. A known technique is the application layer anycast (ALA). The main goal of this work is to elaborate efficient ways to provide ALA with quality of service in the context of cloud computing. To achieve this goal, we proposed a new algorithm (GALA, Global Application Layer Anycast). It inherits characteristics from another existing system (GAA, Global Application-layer Anycast), and uses geolocation as a differential. The results of the experiments show that GALA, compared to the inherited algorithm, maintains the client requests efficiencies and substantially lowers their latencies.
2015-05-08T10:48:38Z
A Utility-Aware Runtime Conflict Resolver for Composite Web services
Ning, X.
Xu, J.
Xu, N.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32237
2015-05-09T02:03:40Z
2015-05-08T10:40:16Z
Title: A Utility-Aware Runtime Conflict Resolver for Composite Web services
Authors: Ning, X.; Xu, J.; Xu, N.; Reiff-Marganiec, Stephan
Abstract: Web services are developed independently and
deployed in a distributed environment, new service can be
obtained by composing existing ones. The rapid introduction
of new services also results in undesirable interactions between
services. These conflicts are not mismatches of interfaces, but
are usually based on the data in the executing instance and
therefore runtime management of conflicts in Web services
should be considered. We study the problem from the perspective
of user’s revenue, and propose an online approach to
resolve conflicts is proposed.
2015-05-08T10:40:16Z
Study Case of Restful Frameworks in Raspberry Pi: A Perfomance and Energy Overview
Nunes, L. H.
Nakamura, L. H. V.
De F. Vieira, H.
De O. Libardi, R. M.
De Oliveira, E. M.
Adami, L. J.
Estrella, J. C.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32236
2015-05-09T02:03:38Z
2015-05-08T10:34:01Z
Title: Study Case of Restful Frameworks in Raspberry Pi: A Perfomance and Energy Overview
Authors: Nunes, L. H.; Nakamura, L. H. V.; De F. Vieira, H.; De O. Libardi, R. M.; De Oliveira, E. M.; Adami, L. J.; Estrella, J. C.; Reiff-Marganiec, Stephan
Abstract: This paper analyzes the execution behavior of web
services on devices with limited resources. The experiments
compare web services in the Axis2 and CXF frameworks
analyzing performance and power consumption. To determine
which framework is better suited for service provision, a testing
environment and a performance and energy evaluation between
them are presented. We show that the Raspberry Pi can be
useful in service-oriented applications for different types of
tasks. Bringing together the best features of small devices
and SoC, it is possible to provide diverse, mobile and green
applications.
2015-05-08T10:34:01Z
Fast Selection of Web Services with QoS using a Distributed Parallel Semantic Approach
Nakamura, L. H. V.
do Prado, P. F.
de O. Libardi, R. M.
Nunes, L. H.
Estrella, J. C.
Santana, R. H. C.
Santana, M. J.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32235
2015-09-15T09:34:20Z
2015-05-08T10:25:34Z
Title: Fast Selection of Web Services with QoS using a Distributed Parallel Semantic Approach
Authors: Nakamura, L. H. V.; do Prado, P. F.; de O. Libardi, R. M.; Nunes, L. H.; Estrella, J. C.; Santana, R. H. C.; Santana, M. J.; Reiff-Marganiec, Stephan
Abstract: This paper presents a solution to performance
issues in the quality of service aware selection of Web services
using techniques of parallelism and mechanisms of inference
provided by Semantic Web. The results point to a significant
improvement in the speed of searching Web services and thus
makes the use of semantic resources viable in distributed
systems to provide better quality of service to the clients.
2015-05-08T10:25:34Z
Encoding Data Structures
Raman, Rajeev
http://hdl.handle.net/2381/32217
2015-05-08T02:00:49Z
2015-05-07T13:20:56Z
Title: Encoding Data Structures
Authors: Raman, Rajeev
Abstract: In recent years, there has been an explosion of interest in
succinct data structures, which store the given data in compact or compressed
formats and answer queries on the data rapidly while it is still
in its compressed format. Our focus in this talk is to introduce encoding
data structures. Encoding data structures consider the data together
with the queries and aim to store only as much information about the
data as is needed to store the queries. Once this is done, the original data
can be deleted. In many cases, one can obtain space-efficient encoding
data structures even when the original data is incompressible.
Description: Abstract of invited talk.
2015-05-07T13:20:56Z
Compact Encodings and Indexes for the Nearest Larger Neighbor Problem
Jo, S.
Raman, Rajeev
Satti, S. R.
http://hdl.handle.net/2381/32215
2015-05-08T02:00:55Z
2015-05-07T13:05:29Z
Title: Compact Encodings and Indexes for the Nearest Larger Neighbor Problem
Authors: Jo, S.; Raman, Rajeev; Satti, S. R.
Abstract: Given a d-dimensional array, for any integer d > 0, the nearest
larger value (NLV) query returns the position of the element which
is closest, in L1 distance, to the query position, and is larger than the
element at the query position. We consider the problem of preprocessing
a given array, to construct a data structure that can answer NLV queries
efficiently. In the 2-D case, given an n × n array A, we give an asymptotically
optimal O(n
2
)-bit encoding that answers NLV queries in O(1)
time. When A is a binary array, we describe a simpler O(n
2
)-bit encoding
that also supports NLV queries in O(1) time. Using this, we obtain
an index of size O(n
2
/c) bits that supports NLV queries in O(c) time,
for any parameter c, where 1 ≤ c ≤ n, matching the lower bound. For
the 1-D case we consider the nearest larger right value (NLRV) problem
where the nearest larger value to the right is sought. For an array of
length n, we obtain an index that takes O((n/c) log c) bits, and supports
NLRV queries in O(c) time, for any any parameter c, where 1 ≤ c ≤ n,
improving the earlier results of Fischer et al. and Jayapaul et al.
2015-05-07T13:05:29Z
Black-Box Test Generation from Inferred Models
Papadopoulos, Petros
Walkinshaw, Neil
http://hdl.handle.net/2381/32206
2015-08-25T01:45:08Z
2015-05-07T10:44:39Z
Title: Black-Box Test Generation from Inferred Models
Authors: Papadopoulos, Petros; Walkinshaw, Neil
Abstract: Automatically generating test inputs for components
without source code (are ‘black-box’) and specification is challenging.
One particularly interesting solution to this problem is to
use Machine Learning algorithms to infer testable models from
program executions in an iterative cycle. Although the idea has
been around for over 30 years, there is little empirical information
to inform the choice of suitable learning algorithms, or to show
how good the resulting test sets are. This paper presents an
openly available framework to facilitate experimentation in this
area, and provides a proof-of-concept inference-driven testing
framework, along with evidence of the efficacy of its test sets on
three programs.
2015-05-07T10:44:39Z
Decoding the regulatory network for blood development from single cell gene expression measurements
Piterman, Nir
Moignard, V.
Woodhouse, S.
Haghverdi, L.
Lilly, J.
Tanaka, Y.
Wilkinson, A.
Buettner, F.
Macaulay, I.
Jawaid, W.
Diamanti, E.
Nishikawa, S.-I.
Kouskoff, V.
Theis, F.
Fisher, J.
http://hdl.handle.net/2381/32202
2015-09-26T01:45:07Z
2015-05-07T10:43:26Z
Title: Decoding the regulatory network for blood development from single cell gene expression measurements
Authors: Piterman, Nir; Moignard, V.; Woodhouse, S.; Haghverdi, L.; Lilly, J.; Tanaka, Y.; Wilkinson, A.; Buettner, F.; Macaulay, I.; Jawaid, W.; Diamanti, E.; Nishikawa, S.-I.; Kouskoff, V.; Theis, F.; Fisher, J.
Description: 6 month embargo
2015-05-07T10:43:26Z
Tree Compression with Top Trees Revisited
Hübschle-Schneider, L.
Raman, Rajeev
http://hdl.handle.net/2381/32187
2015-06-29T08:41:04Z
2015-05-07T10:28:34Z
Title: Tree Compression with Top Trees Revisited
Authors: Hübschle-Schneider, L.; Raman, Rajeev
Abstract: We revisit tree compression with top trees (Bille et al. Information & Computation 2015), and present several improvements to the compressor and its analysis. By significantly reducing the amount of information stored and guiding the compression step using a RePair-inspired heuristic, we obtain a fast compressor achieving good compression ratios, addressing an open problem posed by Bille et al. We show how, with relatively small overhead, the compressed file can be converted into an in-memory representation that supports basic navigation operations in worst-case logarithmic time without decompression. We also show a much improved worst-case bound on the size of the output of top-tree compression (answering an open question posed in a talk on this algorithm by Weimann in 2012).
2015-05-07T10:28:34Z
Random access to grammar-compressed strings and trees
Bille, P.
Landau, G. M.
Raman, Rajeev
Sadakane, K.
Satti, S. R.
Weimann, O.
http://hdl.handle.net/2381/32182
2015-06-03T02:00:11Z
2015-05-07T10:26:27Z
Title: Random access to grammar-compressed strings and trees
Authors: Bille, P.; Landau, G. M.; Raman, Rajeev; Sadakane, K.; Satti, S. R.; Weimann, O.
Abstract: Grammar based compression, where one replaces a long string by a small context-free
grammar that generates the string, is a simple and powerful paradigm that captures (sometimes with
slight reduction in efficiency) many of the popular compression schemes, including the Lempel-Ziv
family, Run-Length Encoding, Byte-Pair Encoding, Sequitur, and Re-Pair. In this paper, we present
a novel grammar representation that allows efficient random access to any character or substring
without decompressing the string.
Let S be a string of length N compressed into a context-free grammar S of size n. We present
two representations of S achieving O(log N) random access time, and either O(n·αk(n)) construction
time and space on the pointer machine model, or O(n) construction time and space on the RAM.
Here, αk(n) is the inverse of the k th row of Ackermann’s function. Our representations also efficiently
support decompression of any substring in S: we can decompress any substring of length m in the
same complexity as a single random access query and additional O(m) time. Combining these
results with fast algorithms for uncompressed approximate string matching leads to several efficient
algorithms for approximate string matching on grammar compressed strings without decompression.
For instance, we can find all approximate occurrences of a pattern P with at most k errors in time
O(n(min{|P|k, k^4 + |P|} + log N) + occ), where occ is the number of occurrences of P in S. Finally,
we generalize our results to navigation and other operations on grammar-compressed ordered trees.
All of the above bounds significantly improve the currently best known results. To achieve these
bounds, we introduce several new techniques and data structures of independent interest, including
a predecessor data structure, two “biased” weighted ancestor data structures, and a compact
representation of heavy paths in grammars.
Description: AMS subject classifications. 68P05, 68P30
2015-05-07T10:26:27Z
CPT+: Decreasing the time/space complexity of the Compact Prediction Tree
Gueniche, T.
Fournier-Viger, P.
Raman, Rajeev
Tseng, V.
http://hdl.handle.net/2381/32181
2015-06-05T13:40:30Z
2015-05-07T10:25:53Z
Title: CPT+: Decreasing the time/space complexity of the Compact Prediction Tree
Authors: Gueniche, T.; Fournier-Viger, P.; Raman, Rajeev; Tseng, V.
Abstract: Predicting next items of sequences of symbols has many applications in a wide range of domains. Several sequence prediction models have been proposed such as DG, All-k-order markov and PPM. Recently, a model named Compact Prediction Tree (CPT) has been proposed. It relies on a tree structure and a more complex prediction algorithm to offer considerably more accurate predictions than many state-of-the-art prediction models. However, an important limitation of CPT is its high time and space complexity. In this article, we address this issue by proposing three novel strategies to reduce CPT’s size and prediction time, and increase its accuracy. Experimental results on seven real life datasets show that the resulting model (CPT+) is up to 98 times more compact and 4.5 times faster than CPT, and has the best overall accuracy when compared to six state-of-the-art models from the literature: All-K-order Markov, CPT, DG, Lz78, PPM and TDAG.
Description: Accepted as "REGULAR PAPER WITH LONG PRESENTATION" 27 of 405 submisisons accepted in this category.
2015-05-07T10:25:53Z
Encoding Nearest Larger Values
Nicholson, P. K.
Raman, Rajeev
http://hdl.handle.net/2381/32178
2015-06-23T15:57:32Z
2015-05-07T10:24:32Z
Title: Encoding Nearest Larger Values
Authors: Nicholson, P. K.; Raman, Rajeev
Abstract: In nearest larger value (NLV) problems, we are given an array A[1..n] of numbers, and need to preprocess A to answer queries of the following form: given any index i ∈ [1, n], return a “nearest” index j such that A[j] > A[i]. We consider the variant where the values in A are distinct, and we wish to return an index j such that A[j] > A[i] and |j − i| is minimized, the nondirectional NLV (NNLV) problem. We consider NNLV in the encoding model, where the array A is delete after preprocessing, and note that NNLV encoding problem has an unexpectedly rich structure: the effective entropy (optimal space usage) of the problem depends crucially on details in the definition of the problem. Using a new path-compressed representation of binary trees, that may have other applications, we encode NNLV in 1.9n + o(n) bits, and answer queries in O(1) time.
2015-05-07T10:24:32Z
Local Reputation Management in Cloud Computing
Jiang, D.
Xu, J.
Yang, D.
Reiff-Marganiec, Stephan
http://hdl.handle.net/2381/32148
2015-08-26T01:45:08Z
2015-05-07T10:06:10Z
Title: Local Reputation Management in Cloud Computing
Authors: Jiang, D.; Xu, J.; Yang, D.; Reiff-Marganiec, Stephan
Abstract: In the Cloud computing community, the calculation
of the reputation using the feedback of cloud customers is
widely adopted to address the issue of trustworthiness of cloud
services. Currently, most methods pursue a global reputation
score essentially assuming that the value of a cloud service’s
reputation is the same for every consumer. However depending
on the expectations and needs of a consumer, there can be
significant deviation of perceived reputation for the same cloud
service. In this paper we propose a trust management framework
that differentiates reputation for various user groups
thus providing what we term local reputation. To achieve this
we compute the similarity of consumers based a decision-tree
model which is used to cluster feedback into localised scores.
To refine the result, a time decay factor applicable to feedback
is also to be considered. The simulation results illustrate that
our approach is feasible and also effective for consumers to
choose reputable cloud service.
2015-05-07T10:06:10Z
On Temporal Graph Exploration
Erlebach, Thomas
Hoffmann, Michael
Kammer, F.
http://hdl.handle.net/2381/32123
2015-07-13T11:40:41Z
2015-05-07T09:24:41Z
Title: On Temporal Graph Exploration
Authors: Erlebach, Thomas; Hoffmann, Michael; Kammer, F.
Editors: Speckmann, B.; Kobayashi, N.; Halldorsson, M. M.
Abstract: A temporal graph is a graph in which the edge set can change from step to step. The temporal graph exploration problem TEXP is the problem of computing a foremost exploration schedule for a temporal graph, i.e., a temporal walk that starts at a given start node, visits all nodes of the graph, and has the smallest arrival time. We consider only temporal graphs that are connected at each step. For such temporal graphs with $n$ nodes, we show that it is $\NP$-hard to approximate TEXP with ratio $O(n^{1-\epsilon})$ for any $\epsilon>0$. We also provide an explicit construction of temporal graphs that require $\Theta(n^2)$ steps to be explored. We then consider TEXP under the assumption that the underlying graph (i.e. the graph that contains all edges that are present in the temporal graph in at least one step) belongs to a specific class of graphs. Among other results, we show that temporal graphs can be explored in $O(n^{1.5}k^2\log n)$ steps if the underlying graph has treewidth $k$ and in $O(n\log^3 n)$ steps if the underlying graph is a $2\times n$ grid. Finally, we show that sparse temporal graphs with regularly present edges can always be explored in $O(n)$ steps.
2015-05-07T09:24:41Z
MSSF: A step towards user-friendly multi-cloud data dispersal
Libardi, R. M. de O.
Bedo, M. V. N.
Reiff-Marganiec, Stephan
Estrella, Julio C.
http://hdl.handle.net/2381/32118
2015-05-07T02:00:20Z
2015-05-06T12:06:35Z
Title: MSSF: A step towards user-friendly multi-cloud data dispersal
Authors: Libardi, R. M. de O.; Bedo, M. V. N.; Reiff-Marganiec, Stephan; Estrella, Julio C.
Abstract: With an increasing number of companies and individuals
adopting cloud computing for their data needs. Naturally,
there is a shift in financial and operational costs and and provided
services should meet users’ performance and cost expectations.
We focus on storage and propose MSSF, a Multi-cloud Storage
Selection Framework. MSSF contains a basic set of algorithms,
a set of security rules and a formal definition of user profiles
allowing to fit cloud storage services to user needs. Preliminary
experiments investigate the cost differences between two baseline
algorithms and user profile models. Considering the promising
initial results we provide several observations about the MSSF
decision making process that will help with future improvements.
2015-05-06T12:06:35Z
Survey of Aspect-Oriented Analysis and Design Approaches
Chitchyan, Ruzanna
Rashid, A.
Sawyer, P.
Garcia, A.
Alarcon, M. P.
Bakker, J.
Tekinerdogan, B.
Clarke, S.
Jackson, A.
http://hdl.handle.net/2381/32112
2015-05-18T01:45:07Z
2015-05-05T11:06:43Z
Title: Survey of Aspect-Oriented Analysis and Design Approaches
Authors: Chitchyan, Ruzanna; Rashid, A.; Sawyer, P.; Garcia, A.; Alarcon, M. P.; Bakker, J.; Tekinerdogan, B.; Clarke, S.; Jackson, A.
Abstract: A number of Aspect-Oriented (AO) Requirements, Architecture, and Design approaches have emerged recently. In this report we survey the most significant of these approaches, considering their origins, aims, and contributions. Alongside the AO approaches, we also analyse some of the contemporary non-AO work in order to bring out the differences between two sets of techniques, and to understand the potential contributions of aspect-oriented analysis and design. We also provide some initial insights into processes for AO requirements engineering, analysis and design which may serve as basis for integration of the work of the AOSD- EUROPE project partners. We also outline some issues relevant to such integration.
2015-05-05T11:06:43Z
Tractable Probabilistic μ-Calculus that Expresses Probabilistic Temporal Logics
Castro, P.
Kilmurray, C.
Piterman, Nir
http://hdl.handle.net/2381/32065
2015-04-25T02:04:03Z
2015-04-24T16:40:02Z
Title: Tractable Probabilistic μ-Calculus that Expresses Probabilistic Temporal Logics
Authors: Castro, P.; Kilmurray, C.; Piterman, Nir
Abstract: We revisit a recently introduced probabilistic μ-calculus and study an expressive fragment of it. By using the probabilistic quantification as an atomic operation of the calculus we establish a connection between the calculus and obligation games. The calculus we consider is strong enough to encode well-known logics such as pCTL and pCTL*. Its game semantics is very similar to the game semantics of the classical μ-calculus (using parity obligation games instead of parity games). This leads to an optimal complexity of NP intersection co-NP for its finite model checking procedure. Furthermore, we investigate a (relatively) well-behaved fragment of this calculus: an extension of pCTL with fixed points. An important feature of this extended version of pCTL is that its model checking is only exponential w.r.t. the alternation depth of fixed points, one of the main characteristics of Kozen's μ-calculus.
Description: 1998 ACM Subject Classification F.4.1 Mathematical Logic
2015-04-24T16:40:02Z