DSpace Collection:
http://hdl.handle.net/2117/3093
20150329T06:14:02Z

Trustworthiness in P2P: performance behaviour of two fuzzybased systems for JXTAoverlay platform
http://hdl.handle.net/2117/27102
Title: Trustworthiness in P2P: performance behaviour of two fuzzybased systems for JXTAoverlay platform
Authors: Spaho, Evjola; Sakamoto, Shinji; Barolli, Leonard; Xhafa Xhafa, Fatos; Ikeda, Makoto
Abstract: Peertopeer (P2P) networks, will be very important for future distributed systems and applications. In such networks, peers are heterogeneous in providing the services and they do not have the same competence of reliability. Therefore, it is necessary to estimate whether a peer is trustworthy or not for file sharing and other services. In this paper, we propose two fuzzybased trustworthiness system for P2P communication in JXTAoverlay. System 1 has only one fuzzy logic controller (FLC) and uses four input parameters: mutually agreed behaviour (MAB), actual behaviour criterion (ABC), peer disconnections (PD) and number of uploads (NU) and the output is peer reliability (PR). System 2 has two FLCs. In FLC1 use three input parameters: number of jobs (NJ), number of connections (NC) and connection lifetime (CL) and the output is actual behavioural criterion (ABC). We use ABC and reputation (R) as input linguistic parameters for FLC2 and the output is peer reliability (PR). We evaluate the proposed systems by computer simulations. The simulation results show that the proposed systems have a good behaviour and can be used successfully to evaluate the reliability of the new peer connected in JXTAoverlay.
20150327T15:44:52Z

Measuring precision of modeled behavior
http://hdl.handle.net/2117/26715
Title: Measuring precision of modeled behavior
Authors: Adriansyah, Arya; Muñoz Gama, Jorge; Carmona Vargas, Josep; Van Dongen, Boudewijn; van der Aalst, Wil M. P.
Abstract: Conformance checking techniques compare observed behavior (i.e., event logs) with modeled behavior for a variety of reasons. For example, discrepancies between a normative process model and recorded behavior may point to fraud or inefficiencies. The resulting diagnostics can be used for auditing and compliance management. Conformance checking can also be used to judge a process model automatically discovered from an event log. Models discovered using different process discovery techniques need to be compared objectively. These examples illustrate just a few of the many use cases for aligning observed and modeled behavior. Thus far, most conformance checking techniques focused on replay fitness, i.e., the ability to reproduce the event log. However, it is easy to construct models that allow for lots of behavior (including the observed behavior) without being precise. In this paper, we propose a method to measure precision of process models, given their event logs by first aligning the logs to the models. This way, the measurement is not sensitive to nonfitting executions and more accurate values can be obtained for nonfitting logs. Furthermore, we introduce several variants of the technique to deal better with incomplete logs and reduce possible bias due to behavioral property of process models. The approach has been implemented in the ProM 6 framework and tested against both artificial and reallife cases. Experiments show that the approach is robust to noise and applicable to handle logs and models of reallife complexity.
20150316T11:04:52Z

Degree lower bounds of towertype for approximating formulas with parity quantifiers
http://hdl.handle.net/2117/26697
Title: Degree lower bounds of towertype for approximating formulas with parity quantifiers
Authors: Atserias Peri, Albert; Dawar, Anuj
Abstract: Kolaitis and Kopparty have shown that for any firstorder formula with parity quantifiers over the language of graphs, there is a family of multivariate polynomials of constantdegree that agree with the formula on all but a 2(Omega(n))fraction of the graphs with n vertices. The proof bounds the degree of the polynomials by a tower of exponentials whose height is the nesting depth of parity quantifiers in the formula. We show that this towertype dependence is necessary. We build a family of formulas of depth q whose approximating polynomials must have degree bounded from below by a tower of exponentials of height proportional to q. Our proof has two main parts. First, we adapt and extend the results by Kolaitis and Kopparty that describe the joint distribution of the parities of the numbers of copies of small subgraphs in a random graph to the setting of graphs of growing size. Second, we analyze a variant of Karp's graph canonical labeling algorithm and exploit its massive parallelism to get a formula of low depth that defines an almost canonical preorder on a random graph.
20150313T13:18:21Z

Cooperation through social influence
http://hdl.handle.net/2117/26600
Title: Cooperation through social influence
Authors: Molinero Albareda, Xavier; Riquelme Csori, Fabián; Serna Iglesias, María José
Abstract: We consider a simple and altruistic multiagent system in which the agents are eager to perform a collective task but where their real engagement depends on the willingness to perform the task of other influential agents. We model this scenario by an influence game, a cooperative simple game in which a team (or coalition) of players succeeds if it is able to convince enough agents to participate in the task (to vote in favor of a decision). We take the linear threshold model as the influence model. We show first the expressiveness of influence games showing that they capture the class of simple games. Then we characterize the computational complexity of various problems on influence games, including measures (length and width), values (ShapleyShubik and Banzhaf) and properties (of teams and players). Finally, we analyze those problems for some particular extremal cases, with respect to the propagation of influence, showing tighter complexity characterizations.
20150305T17:47:09Z

On the complexity of problems on simple games
http://hdl.handle.net/2117/25093
Title: On the complexity of problems on simple games
Authors: Freixas Bosch, Josep; Molinero Albareda, Xavier; Olsen, Martin; Serna Iglesias, María José
Abstract: Simple games cover voting systems in which a single alter
native, such as a bill or an amendment, is pitted against the status quo. A simple game or a yesno voting system is a set of rules that specifies exactly which collections of “yea” votes yield passage of the issue at hand. Each of these collections of “yea” voters forms a winning coalition. We are interested in performing a complexity analysis on problems defined on such families of games. This analysis as usual depends on the game representation used as input. We consider four natural explicit representations: winning, losing, minimal winning, and maximal losing. We first analyze the complexity of testing whether a game is simple and testing whether a game is weighted. We show that, for the four types of representations, both problems can be solved in polynomial time. Finally, we provide results on the complexity of testing whether a simple game or a weighted game is of a special type. We analyze strongness, properness, weightedness, homogeneousness, decisiveness and majorityness, which are desirable properties to be fulfilled for a simple game.
Finally, we consider the possibility of representing a game in a more
succinct and natural way and show that the corresponding recognition
problem is hard.
20141218T19:12:37Z

Long noncoding RNAs as a source of new peptides
http://hdl.handle.net/2117/24421
Title: Long noncoding RNAs as a source of new peptides
Authors: Ruiz Orera, Jorge; Messeguer Peypoch, Xavier; Subirana Torrent, Juan A.; Albà Soler, M. Mar
Abstract: Deep transcriptome sequencing has revealed the existence of many transcripts that lack long or conserved open reading frames (ORFs) and which have been termed long noncoding RNAs (lncRNAs). The vast majority of lncRNAs are lineagespecific and do not yet have a known function. In this study, we test the hypothesis that they may act as a repository for the synthesis of new peptides. We find that a large fraction of the lncRNAs expressed in cells from six different species is associated with ribosomes. The patterns of ribosome protection are consistent with the translation of short peptides. lncRNAs show similar coding potential and sequence constraints than evolutionary young protein coding sequences, indicating that they play an important role in de novo protein evolution.
20141020T08:38:40Z

Power indices of influence games and new centrality measures for agent societies and social networks
http://hdl.handle.net/2117/24245
Title: Power indices of influence games and new centrality measures for agent societies and social networks
Authors: Molinero Albareda, Xavier; Riquelme Csori, Fabián; Serna Iglesias, María José
Abstract: We propose as centrality measures for social networks two classical power indices, Banzhaf and ShapleyShubik, and two new measures, effort and satisfaction, related to the spread of influence process that emerge from the subjacent influence game. We perform a comparison of these measures with three well known centrality measures, degree, closeness and betweenness, applied to three simple social networks.
20141003T13:58:17Z

Singleentry singleexit decomposed conformance checking
http://hdl.handle.net/2117/23672
Title: Singleentry singleexit decomposed conformance checking
Authors: Muñoz Gama, Jorge; Carmona Vargas, Josep; Van der Aalst, Wil M. P.
Abstract: An exponential growth of event data can be witnessed across all industries. Devices connected to the internet (internet of things), social interaction, mobile computing, and cloud computing provide new sources of event data and this trend will continue. The omnipresence of large amounts of event data is an important enabler for process mining. Process mining techniques can be used to discover, monitor and improve real processes by extracting knowledge from observed behavior. However, unprecedented volumes of event data also provide new challenges and often stateoftheart process mining techniques cannot cope. This paper focuses on “conformance checking in the large” and presents a novel decomposition technique that partitions larger process models and event logs into smaller parts that can be analyzed independently. The socalled SingleEntry SingleExit (SESE) decomposition not only helps to speed up conformance checking, but also provides improved diagnostics. The analyst can zoom in on the problematic parts of the process. Importantly, the conditions under which the conformance of the whole can be assessed by verifying the conformance of the SESE parts are described, which enables the decomposition and distribution of large conformance checking problems. All the techniques have been implemented in ProM, and experimental results are provided.
20140801T12:25:50Z

Reasoning about orchestrations of web services using partial correctness
http://hdl.handle.net/2117/23530
Title: Reasoning about orchestrations of web services using partial correctness
Authors: Stewart, Alan; Gabarró Vallès, Joaquim; Keenan, Anthony
Abstract: A service is a remote computational facility which is made available for general use by means of a
widearea network. Several types of service arise in practice: stateless services, shared state services and services
with states which are customised for individual users. A servicebased orchestration is a multithreaded compu
tation which invokes remote services in order to deliver results back to a user (publication). In this paper a means
of specifying services and reasoning about the correctness of orchestrations over
stateless
services is presented.
As web services are potentially unreliable the termination of even finite orchestrations cannot be guaranteed.
For this reason a partialcorrectness powerdomain approach is proposed to capture the semantics of recursive
orchestrations.
20140716T12:57:09Z

Excessively duplicating patterns represent nonregular languages
http://hdl.handle.net/2117/23504
Title: Excessively duplicating patterns represent nonregular languages
Authors: Creus López, Carles; Godoy Balil, Guillem; Ramos Garrido, Lander
Abstract: A constrained term pattern s:¿ represents the language of all instances of the term s satisfying the constraint ¿. For each variable in s, this constraint specifies the language of its allowed substitutions. Regularity of languages represented by sets of patterns has been studied for a long time. This problem is known to be coNPcomplete when the constraints allow each variable to be replaced by any term over a fixed signature, and EXPTIMEcomplete when the constraints restrict each variable to a regular set. In both cases, duplication of variables in the terms of the patterns is a necessary condition for nonregularity. This is because duplications force the recognizer to test equality between subterms. Hence, for the specific classes of constraints mentioned above, if all patterns are linear, then the represented language is necessarily regular. In this paper we focus on the opposite case, that is when there are patterns with
20140714T12:29:43Z

Turing's algorithmic lens: from computability to complexity theory
http://hdl.handle.net/2117/22738
Title: Turing's algorithmic lens: from computability to complexity theory
Authors: Díaz Cort, Josep; Torras, Carme
Abstract: The decidability question, i.e., whether any mathematical statement could be computationally proven true or false, was raised by Hilbert and remained open until Turing answered it in the negative. Then, most efforts in theoretical computer science turned to complexity theory and the need to classify decidable problems according to their difficulty. Among others, the classes P (problems solvable in polynomial time) and NP (problems solvable in nondeterministic polynomial time) were defined, and one of the most challenging scientific quests of our days arose: whether P = NP. This still open question has implications not only in computer science, mathematics and physics, but also in biology, sociology and economics, and it can be seen as a direct consequence of Turing’s way of looking through the algorithmic lens at different disciplines to discover how pervasive computation is.
20140428T17:13:15Z

Emptiness and finiteness for tree automata with global reflexive disequality constraints
http://hdl.handle.net/2117/22680
Title: Emptiness and finiteness for tree automata with global reflexive disequality constraints
Authors: Creus López, Carles; Gascón Caro, Adrià; Godoy Balil, Guillem
Abstract: In recent years, several extensions of tree automata have been considered. Most of them are related with the capability of testing equality or disequality of certain subterms of the term evaluated by the automaton. In particular, tree automata with global constraints are able to test equality and disequality of subterms depending on the state to which they are evaluated. The emptiness problem is known decidable for this kind of automata, but with a nonelementary time complexity, and the finiteness problem remains unknown. In this paper, we consider the particular case of tree automata with global constraints when the constraint is a conjunction of disequalities between states, and the disequality predicate is forced to be reflexive. This restriction is significant in the context of XML definitions with monadic key constraints. We prove that emptiness and finiteness are decidable in triple exponential time for this kind of automata. © 2012 Springer Science+Business Media Dordrecht.
20140423T14:55:34Z

Nonlinear rewrite closure and weak normalization
http://hdl.handle.net/2117/20443
Title: Nonlinear rewrite closure and weak normalization
Authors: Creus López, Carles; Godoy Balil, Guillem; Massanes Basi, Francesc d'Assis; Tiwari, Ashish Kumar
Abstract: A rewrite closure is an extension of a term rewrite system with new rules, usually deduced by transitivity. Rewrite closures have the nice property that all rewrite derivations can be transformed into derivations of a simple form. This property has been useful for proving decidability results in term rewriting. Unfortunately, when the term rewrite system is not linear, the construction of a rewrite closure is quite challenging. In this paper, we construct a rewrite closure for term rewrite systems that satisfy two properties: the righthand side term in each rewrite rule contains no repeated variable (rightlinear) and contains no variable occurring at depth greater than one (rightshallow). The lefthand side term is unrestricted, and in particular, it may be nonlinear. As a consequence of the rewrite closure construction, we are able to prove decidability of the weak normalization problem for rightlinear rightshallow term rewrite systems. Proving this result also requires tree automata theory. We use the fact that rightshallow rightlinear term rewrite systems are regularity preserving. Moreover, their set of normal forms can be represented with a tree automaton with disequality constraints, and emptiness of this kind of automata, as well as its generalization to reduction automata, is decidable. A preliminary version of this work was presented at LICS 2009.
20131022T12:42:27Z

Architectural exploration of largescale hierarchical chip multiprocessors
http://hdl.handle.net/2117/20442
Title: Architectural exploration of largescale hierarchical chip multiprocessors
Authors: Nikitin, Nikita; San Pedro Martín, Javier de; Cortadella Fortuny, Jordi
Abstract: The continuous scaling of nanoelectronics is increasing the complexity of chip multiprocessors (CMPs) and exacerbating the memory wall problem. As CMPs become more complex, the memory subsystem is organized into more hierarchical structures to better exploit locality. To efficiently discover promising architectures within the rapidly growing search space, exhaustive exploration is replaced with tools that implement intelligent search strategies. Moreover, faster analytical models are preferred to costly simulations for estimating the performance and power of CMP architectures. The memory traffic generated by CMP cores has a cyclic dependency with the latency of the memory subsystem, which critically affects the overall system performance. Based on this observation, a novel scalable analytical method is proposed to estimate the performance of highly parallel CMPs (hundreds or thousands of cores) with hierarchical interconnect networks. The method can use customizable probabilistic models and solves the cyclic dependencies between traffic and latency by using a fixedpoint strategy. By using the analytical model as a performance and power estimator, an efficient metaheuristicbased search is proposed for the exploration of large design spaces. The proposed techniques are shown to be very accurate and a promising strategy when compared to the results obtained by simulation.
20131022T12:34:01Z

Decidable classes of tree automata mixing local and global constraints modulo flat theories
http://hdl.handle.net/2117/20262
Title: Decidable classes of tree automata mixing local and global constraints modulo flat theories
Authors: Barguño, Luis; Creus López, Carles; Godoy Balil, Guillem; Jacquemard, Florent; Vacher, Camile
Abstract: We define a class of ranked tree automata TABG generalizing both the tree automata with local tests between brothers of Bogaert and Tison (1992) and with global equality and disequality constraints (TAGED) of Filiot et al. (2007). TABG can test for
equality and disequality modulo a given flat equational theory between brother subterms
and between subterms whose positions are defined by the states reached during a computation.
In particular, TABG can check that all the subterms reaching a given state are distinct. This constraint is related to monadic key constraints for XML documents,
meaning that every two distinct positions of a given type have different values. We prove decidability of the emptiness problem for TABG. This solves, in particular, the open question of the decidability of emptiness for TAGED. We further extend our result by allowing global arithmetic constraints for counting the number of occurrences of some state or the number of different equivalence classes of subterms (modulo a given flat equational theory) reaching some state during a computation. We also adapt the
model to unranked ordered terms. As a consequence of our results for TABG, we prove
the decidability of a fragment of the monadic second order logic on trees extended with predicates for equality and disequality between subtrees, and cardinality.
20131002T11:49:06Z