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http://hdl.handle.net/2117/3095
Sat, 25 Oct 2014 15:29:49 GMT
20141025T15:29:49Z
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Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació
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Narrow proofs may be maximally long
http://hdl.handle.net/2117/24406
Title: Narrow proofs may be maximally long
Authors: Atserias Peri, Albert; Lauria, Massimo; Nordström, Jakob
Abstract: We prove that there are 3CNF formulas over n variables that can be refuted in resolution in width w but require resolution proofs of size n¿(w). This shows that the simple counting argument that any formula refutable in width w must have a proof in size nO(¿) is essentially tight. Moreover, our lower bounds can be generalized to polynomial calculus resolution (PCR) and SheraliAdams, implying that the corresponding size upper bounds in terms of degree and rank are tight as well. Our results do not extend all the way to Lasserre, howeverthe formulas we study have Lasserre proofs of constant rank and size polynomial in both n and w.
Fri, 17 Oct 2014 11:02:37 GMT
http://hdl.handle.net/2117/24406
20141017T11:02:37Z
Atserias Peri, Albert; Lauria, Massimo; Nordström, Jakob
no
Degree, Lasserre, Length, PCR, Polynomial calculus, Proof complexity, Rank, Resolution, SheraliAdams, Size, Width
We prove that there are 3CNF formulas over n variables that can be refuted in resolution in width w but require resolution proofs of size n¿(w). This shows that the simple counting argument that any formula refutable in width w must have a proof in size nO(¿) is essentially tight. Moreover, our lower bounds can be generalized to polynomial calculus resolution (PCR) and SheraliAdams, implying that the corresponding size upper bounds in terms of degree and rank are tight as well. Our results do not extend all the way to Lasserre, howeverthe formulas we study have Lasserre proofs of constant rank and size polynomial in both n and w.

Correctness of incremental model synchronization with triple graph grammars
http://hdl.handle.net/2117/24364
Title: Correctness of incremental model synchronization with triple graph grammars
Authors: Orejas Valdés, Fernando; Pino Blanco, Elvira
Abstract: In modeldriven software development, we may have several models describing the same system or artifact, by providing different views on it. In this case, we say that these models are consistently integrated. Triple Graph Grammars (TGGs), defined by Schürr, are a general and powerful tool to describe (bidirectional) model transformations. In this context, model synchronization is the operation that, given two consistent models and an update or modification of one of them, finds the corresponding update on the other model, so that consistency is restored. There are different approaches to describe this operation in terms of TGGs, but most of them have a computational cost that depends on the size of the given models. In general this may be very costly since these models may be quite large. To avoid this problem, Giese and Wagner have advocated for the need of incremental synchronization procedures, meaning that their cost should depend only on the size of the given update. In particular they proposed one such procedure. Unfortunately, the correctness of their approach is not studied and, anyhow, it could only be ensured under severe restrictions on the kind of TGGs considered. In the work presented, we study the problem from a different point of view. First, we discuss what it means for a procedure to be incremental, defining a correctness notion that we call incremental consistency. Moreover, we present a general incremental synchronization procedure and we show its correctness, completeness and incrementality.
Tue, 14 Oct 2014 11:38:12 GMT
http://hdl.handle.net/2117/24364
20141014T11:38:12Z
Orejas Valdés, Fernando; Pino Blanco, Elvira
no
Incremental model synchronization, Model synchronization, Model transformation, Triple graph grammars
In modeldriven software development, we may have several models describing the same system or artifact, by providing different views on it. In this case, we say that these models are consistently integrated. Triple Graph Grammars (TGGs), defined by Schürr, are a general and powerful tool to describe (bidirectional) model transformations. In this context, model synchronization is the operation that, given two consistent models and an update or modification of one of them, finds the corresponding update on the other model, so that consistency is restored. There are different approaches to describe this operation in terms of TGGs, but most of them have a computational cost that depends on the size of the given models. In general this may be very costly since these models may be quite large. To avoid this problem, Giese and Wagner have advocated for the need of incremental synchronization procedures, meaning that their cost should depend only on the size of the given update. In particular they proposed one such procedure. Unfortunately, the correctness of their approach is not studied and, anyhow, it could only be ensured under severe restrictions on the kind of TGGs considered. In the work presented, we study the problem from a different point of view. First, we discuss what it means for a procedure to be incremental, defining a correctness notion that we call incremental consistency. Moreover, we present a general incremental synchronization procedure and we show its correctness, completeness and incrementality.

Processoriented analysis for medical devices
http://hdl.handle.net/2117/24363
Title: Processoriented analysis for medical devices
Authors: Sfyrla, Vassiliki; Carmona Vargas, Josep; Henck, Pascal
Abstract: Medical Cyber Physical Systems are widely used in modern healthcare environments. Such systems are considered lifecritical due to the severity of consequences that faults may cause. Effective methods, techniques and tools for modeling and analyzing medical critical systems are of major importance for ensuring system reliability and patient safety. This work is looking at issues concerning different types of medical industry needs including safety analysis, testing, conformance checking, performance analysis and optimization. We explore the possibility of addressing these issues by exploiting information recorded in logs generated by medical devices during execution. Processoriented analysis of logs is known as process mining, a novel field that has gained considerable interest in several contexts in the last decade. Process mining techniques will be applied to an industrial use case provided by Fresenius, a manufacturer of medical devices, for analyzing process logs generated by an infusion pump.
Tue, 14 Oct 2014 09:28:19 GMT
http://hdl.handle.net/2117/24363
20141014T09:28:19Z
Sfyrla, Vassiliki; Carmona Vargas, Josep; Henck, Pascal
no
Discovery, Formal analysis, Infusion pump, Process logs, Process mining
Medical Cyber Physical Systems are widely used in modern healthcare environments. Such systems are considered lifecritical due to the severity of consequences that faults may cause. Effective methods, techniques and tools for modeling and analyzing medical critical systems are of major importance for ensuring system reliability and patient safety. This work is looking at issues concerning different types of medical industry needs including safety analysis, testing, conformance checking, performance analysis and optimization. We explore the possibility of addressing these issues by exploiting information recorded in logs generated by medical devices during execution. Processoriented analysis of logs is known as process mining, a novel field that has gained considerable interest in several contexts in the last decade. Process mining techniques will be applied to an industrial use case provided by Fresenius, a manufacturer of medical devices, for analyzing process logs generated by an infusion pump.

On the average performance of fixed partial match queries in random relaxed Kd trees
http://hdl.handle.net/2117/24268
Title: On the average performance of fixed partial match queries in random relaxed Kd trees
Authors: Duch Brown, Amalia; Lau LaynesLozada, Gustavo Salvador; Martínez Parra, Conrado
Abstract: We obtain an explicit formula for the expected cost of a fixed partial match query in a random relaxed Kd tree, that is, the expected cost for a query of the form q = (q0 , q1 , . . . , qK1 ) with 0 < s < K specified coordinates with values z0 , . . . , zs1 ¿ (0, 1). This is a generalization of previous results in the literature for s = 1. Qualitatively similar results hold for standard Kd trees and we conjecture that this also holds for other multidimensional tree structures such as quadtrees and Kd tries.
Mon, 06 Oct 2014 09:14:06 GMT
http://hdl.handle.net/2117/24268
20141006T09:14:06Z
Duch Brown, Amalia; Lau LaynesLozada, Gustavo Salvador; Martínez Parra, Conrado
no
Partial match, Kd trees, Multidimensional data structures, Associative queries
We obtain an explicit formula for the expected cost of a fixed partial match query in a random relaxed Kd tree, that is, the expected cost for a query of the form q = (q0 , q1 , . . . , qK1 ) with 0 < s < K specified coordinates with values z0 , . . . , zs1 ¿ (0, 1). This is a generalization of previous results in the literature for s = 1. Qualitatively similar results hold for standard Kd trees and we conjecture that this also holds for other multidimensional tree structures such as quadtrees and Kd tries.

Automatic evaluation of reductions between NPcomplete problems
http://hdl.handle.net/2117/24254
Title: Automatic evaluation of reductions between NPcomplete problems
Authors: Creus López, Carles; Fernández Durán, Pau; Godoy Balil, Guillem
Abstract: We implement an online judge for evaluating correctness of reductions between NPcomplete problems. The site has a list of exercises asking for a reduction between two given problems. Internally, the reduction is evaluated by means of a set of tests. Each test consists of an input of the first problem and gives rise to an input of the second problem through the reduction. The correctness of the reduction, that is, the preservation of the answer between both problems, is checked by applying additional reductions to SAT and using a stateoftheart SAT solver. In order to represent the reductions, we have defined a new programming language called REDNP. On one side, REDNP has specific features for describing typical concepts that frequently appear in reductions, like graphs and clauses. On the other side, we impose severe limitations to REDNP in order to avoid malicious submissions, like the ones with an embedded SAT solver.
Sun, 05 Oct 2014 06:34:30 GMT
http://hdl.handle.net/2117/24254
20141005T06:34:30Z
Creus López, Carles; Fernández Durán, Pau; Godoy Balil, Guillem
no
NPcompleteness, Reductions, SAT application, Self learning
We implement an online judge for evaluating correctness of reductions between NPcomplete problems. The site has a list of exercises asking for a reduction between two given problems. Internally, the reduction is evaluated by means of a set of tests. Each test consists of an input of the first problem and gives rise to an input of the second problem through the reduction. The correctness of the reduction, that is, the preservation of the answer between both problems, is checked by applying additional reductions to SAT and using a stateoftheart SAT solver. In order to represent the reductions, we have defined a new programming language called REDNP. On one side, REDNP has specific features for describing typical concepts that frequently appear in reductions, like graphs and clauses. On the other side, we impose severe limitations to REDNP in order to avoid malicious submissions, like the ones with an embedded SAT solver.

Automatic evaluation of contextfree grammars (system description)
http://hdl.handle.net/2117/24226
Title: Automatic evaluation of contextfree grammars (system description)
Authors: Creus López, Carles; Godoy Balil, Guillem
Abstract: We implement an online judge for contextfree grammars. Our system contains a list of problems describing formal languages, and asking for grammars generating them. A submitted proposal grammar receives a verdict of acceptance or rejection depending on whether the judge determines that it is equivalent to the reference solution grammar provided by the problem setter. Since equivalence of contextfree grammars is an undecidable problem, we consider a maximum length l and only test equivalence of the generated languages up to words of length l. This length restriction is very often sufficient for the wellmeant submissions. Since this restricted problem is still NPcomplete, we design and implement methods based on hashing, SAT, and automata that perform well in practice. © 2014 Springer International Publishing Switzerland.
Fri, 03 Oct 2014 07:01:26 GMT
http://hdl.handle.net/2117/24226
20141003T07:01:26Z
Creus López, Carles; Godoy Balil, Guillem
no
Automata theory, Biomineralization, Context free grammars, Differentiation (calculus), automata, equivalence, grammars, hashing, SAT, Context free languages
We implement an online judge for contextfree grammars. Our system contains a list of problems describing formal languages, and asking for grammars generating them. A submitted proposal grammar receives a verdict of acceptance or rejection depending on whether the judge determines that it is equivalent to the reference solution grammar provided by the problem setter. Since equivalence of contextfree grammars is an undecidable problem, we consider a maximum length l and only test equivalence of the generated languages up to words of length l. This length restriction is very often sufficient for the wellmeant submissions. Since this restricted problem is still NPcomplete, we design and implement methods based on hashing, SAT, and automata that perform well in practice. © 2014 Springer International Publishing Switzerland.

Tree automata with height constraints between brothers
http://hdl.handle.net/2117/24225
Title: Tree automata with height constraints between brothers
Authors: Creus López, Carles; Godoy Balil, Guillem
Abstract: We define the tree automata with height constraints between brothers (TACBB H ). Constraints of equalities and inequalities between heights of siblings that restrict the applicability of the rules are allowed in TACBB H. These constraints allow to express natural tree languages like complete or balanced (like AVL) trees. We prove decidability of emptiness and finiteness for TACBB H, and also for a more general class that additionally allows to combine equality and disequality constraints between brothers. © 2014 Springer International Publishing Switzerland.
Fri, 03 Oct 2014 06:29:03 GMT
http://hdl.handle.net/2117/24225
20141003T06:29:03Z
Creus López, Carles; Godoy Balil, Guillem
no
Constraints, Emptiness, Finiteness, TreeAutomata
We define the tree automata with height constraints between brothers (TACBB H ). Constraints of equalities and inequalities between heights of siblings that restrict the applicability of the rules are allowed in TACBB H. These constraints allow to express natural tree languages like complete or balanced (like AVL) trees. We prove decidability of emptiness and finiteness for TACBB H, and also for a more general class that additionally allows to combine equality and disequality constraints between brothers. © 2014 Springer International Publishing Switzerland.

Metastability in betterthanworstcase designs
http://hdl.handle.net/2117/24174
Title: Metastability in betterthanworstcase designs
Authors: Beer, Salomon; Cannizzaro, Marco; Cortadella Fortuny, Jordi; Ginosar, Ran; Lavagno, Luciano
Abstract: BetterThanWorstCaseDesigns use timing speculation to run with a cycle period faster than the one required for worstcase conditions. This speculation may produce timing violations and metastability that result in failures and nondeterministic timing behavior. The effects of these phenomena are not always well understood by designers and researchers in this area. This paper analyzes the impact of timing speculation and the reasons why it is difficult to adopt this paradigm in industrial designs.
Fri, 26 Sep 2014 10:14:18 GMT
http://hdl.handle.net/2117/24174
20140926T10:14:18Z
Beer, Salomon; Cannizzaro, Marco; Cortadella Fortuny, Jordi; Ginosar, Ran; Lavagno, Luciano
no
Metastability, Betterthanworstcase designs, Timing violations, Nondeterministic timing behavior: Timing speculation, Industrial designs
BetterThanWorstCaseDesigns use timing speculation to run with a cycle period faster than the one required for worstcase conditions. This speculation may produce timing violations and metastability that result in failures and nondeterministic timing behavior. The effects of these phenomena are not always well understood by designers and researchers in this area. This paper analyzes the impact of timing speculation and the reasons why it is difficult to adopt this paradigm in industrial designs.

Hardware primitives for the synthesis of multithreaded elastic systems
http://hdl.handle.net/2117/24157
Title: Hardware primitives for the synthesis of multithreaded elastic systems
Authors: Dimitrakopoulos, George N.; Seitanidis, I.; Psarras, A.; Tsiouris, K.; Mattheakis, Pavlos M.; Cortadella Fortuny, Jordi
Abstract: Elastic systems operate in a dataflowlike mode using a distributed scalable control and tolerating variablelatency computations. At the same time, multithreading increases the utilization of processing units and hides the latency of each operation by timemultiplexing operations of different threads in the datapath. This paper proposes a model to unify multithreading and elasticity. A new multithreaded elastic control protocol is introduced supported by lowcost elastic buffers that minimize the storage requirements without sacrificing performance. To enable the synthesis of multithreaded elastic architectures, new hardware primitives are proposed and utilized in two circuit examples to prove the applicability of the proposed approach.
Thu, 25 Sep 2014 09:32:15 GMT
http://hdl.handle.net/2117/24157
20140925T09:32:15Z
Dimitrakopoulos, George N.; Seitanidis, I.; Psarras, A.; Tsiouris, K.; Mattheakis, Pavlos M.; Cortadella Fortuny, Jordi
no
Engineering controlled terms: Elasticity, Hardware
Elastic systems operate in a dataflowlike mode using a distributed scalable control and tolerating variablelatency computations. At the same time, multithreading increases the utilization of processing units and hides the latency of each operation by timemultiplexing operations of different threads in the datapath. This paper proposes a model to unify multithreading and elasticity. A new multithreaded elastic control protocol is introduced supported by lowcost elastic buffers that minimize the storage requirements without sacrificing performance. To enable the synthesis of multithreaded elastic architectures, new hardware primitives are proposed and utilized in two circuit examples to prove the applicability of the proposed approach.

An operational framework to reason about policy behavior in trust management systems
http://hdl.handle.net/2117/24093
Title: An operational framework to reason about policy behavior in trust management systems
Authors: Pasarella Sánchez, Ana Edelmira; Lobo, Jorge
Abstract: In this paper we show that the logical framework proposed by Becker et al. to reason about security policy behavior in a trust management context can be captured by an operational framework that is based on the language proposed by Miller to deal with scoping and/or modules in logic programming in 1989. The framework of Becker et al. uses propositional Horn clauses to represent both policies and credentials, implications in clauses are interpreted in counterfactual logic, a Hilbertstyle proof is defined and a system based on SAT is used to proof whether properties about credentials, permissions and policies are valid in trust management systems, i.e. formulas that are true for all possible policies. Our contribution is to show that instead of using a SAT system, this kind of validation can rely on the operational semantics (derivability relation) of Miller’s language, which is very close to derivability in logic programs, opening up the possibility to extend Becker et al.’s framework to the more practical first order case since Miller’s language is first order.
Thu, 18 Sep 2014 08:12:23 GMT
http://hdl.handle.net/2117/24093
20140918T08:12:23Z
Pasarella Sánchez, Ana Edelmira; Lobo, Jorge
no
In this paper we show that the logical framework proposed by Becker et al. to reason about security policy behavior in a trust management context can be captured by an operational framework that is based on the language proposed by Miller to deal with scoping and/or modules in logic programming in 1989. The framework of Becker et al. uses propositional Horn clauses to represent both policies and credentials, implications in clauses are interpreted in counterfactual logic, a Hilbertstyle proof is defined and a system based on SAT is used to proof whether properties about credentials, permissions and policies are valid in trust management systems, i.e. formulas that are true for all possible policies. Our contribution is to show that instead of using a SAT system, this kind of validation can rely on the operational semantics (derivability relation) of Miller’s language, which is very close to derivability in logic programs, opening up the possibility to extend Becker et al.’s framework to the more practical first order case since Miller’s language is first order.

On the existence of Nash equilibria in strategic search games
http://hdl.handle.net/2117/23999
Title: On the existence of Nash equilibria in strategic search games
Authors: Álvarez Faura, M. del Carme; Duch Brown, Amalia; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios
Abstract: We consider a general multiagent framework in which a set of n agents are roaming a network where m valuable and sharable goods (resources, services, information ....) are hidden in m different vertices of the network. We analyze several strategic situations that arise in this setting by means of game theory. To do so, we introduce a class of strategic games that we call strategic search games. In those games agents have to select a simple path in the network that starts from a predetermined set of initial vertices. Depending on how the value of the retrieved goods is splitted among the agents, we consider two game types: findersshare in which the agents that find a good split among them the corresponding benefit and firstsshare in which only the agents that first find a good share the corresponding benefit. We show that findersshare games always have pure Nash equilibria (pne ). For obtaining this result, we introduce the notion of Nashpreserving reduction between strategic games. We show that findersshare games are Nashreducible to singlesource network congestion games. This is done through a series of Nashpreserving reductions. For firstsshare games we show the existence of games with and without pne. Furthermore, we identify some graph families in which the firstsshare game has always a pne that is computable in polynomial time.
Mon, 08 Sep 2014 11:01:23 GMT
http://hdl.handle.net/2117/23999
20140908T11:01:23Z
Álvarez Faura, M. del Carme; Duch Brown, Amalia; Serna Iglesias, María José; Thilikos Touloupas, Dimitrios
no
Nash equilibria existence, Strategic search games, General multiagent framework
We consider a general multiagent framework in which a set of n agents are roaming a network where m valuable and sharable goods (resources, services, information ....) are hidden in m different vertices of the network. We analyze several strategic situations that arise in this setting by means of game theory. To do so, we introduce a class of strategic games that we call strategic search games. In those games agents have to select a simple path in the network that starts from a predetermined set of initial vertices. Depending on how the value of the retrieved goods is splitted among the agents, we consider two game types: findersshare in which the agents that find a good split among them the corresponding benefit and firstsshare in which only the agents that first find a good share the corresponding benefit. We show that findersshare games always have pure Nash equilibria (pne ). For obtaining this result, we introduce the notion of Nashpreserving reduction between strategic games. We show that findersshare games are Nashreducible to singlesource network congestion games. This is done through a series of Nashpreserving reductions. For firstsshare games we show the existence of games with and without pne. Furthermore, we identify some graph families in which the firstsshare game has always a pne that is computable in polynomial time.

BeamACO for the repetitionfree longest common subsequence problem
http://hdl.handle.net/2117/23345
Title: BeamACO for the repetitionfree longest common subsequence problem
Authors: Blum, Christian; Blesa Aguilera, Maria Josep; Calvo, Borja
Abstract: In this paper we propose a BeamACO approach for a combinatorial optimization problem known as the repetitionfree longest common subsequence problem. Given two input sequences x and y over a finite alphabet S, this problem concerns to find a longest common subsequence of x and y in which no letter is repeated. BeamACO algorithms
are combinations between the metaheuristic ant colony optimization and a deterministic tree search technique called beam search. The algorithm that we present is an adaptation of a previously published BeamACO
algorithm for the classical longest common subsequence problem. The results of the proposed algorithm outperform existing heuristics from the literature.
Tue, 01 Jul 2014 08:44:15 GMT
http://hdl.handle.net/2117/23345
20140701T08:44:15Z
Blum, Christian; Blesa Aguilera, Maria Josep; Calvo, Borja
no
In this paper we propose a BeamACO approach for a combinatorial optimization problem known as the repetitionfree longest common subsequence problem. Given two input sequences x and y over a finite alphabet S, this problem concerns to find a longest common subsequence of x and y in which no letter is repeated. BeamACO algorithms
are combinations between the metaheuristic ant colony optimization and a deterministic tree search technique called beam search. The algorithm that we present is an adaptation of a previously published BeamACO
algorithm for the classical longest common subsequence problem. The results of the proposed algorithm outperform existing heuristics from the literature.

Lower bounds for DNFrefutations of a relativized weak pigeonhole principle
http://hdl.handle.net/2117/23255
Title: Lower bounds for DNFrefutations of a relativized weak pigeonhole principle
Authors: Atserias Peri, Albert; Müller, Moritz; Oliva Valls, Sergi
Abstract: The relativized weak pigeonhole principle states that if at least 2n out of n2 pigeons fly into n holes, then some hole must be doubly occupied. We prove that every DNFrefutation of the CNF encoding of this principle requires size 2((log n)3/2ϵ) for every ε > 0 and every sufficiently large n. For its proof we need to discuss the existence of unbalanced lowdegree bipartite expanders satisfying a certain robustness condition.
Wed, 18 Jun 2014 09:29:06 GMT
http://hdl.handle.net/2117/23255
20140618T09:29:06Z
Atserias Peri, Albert; Müller, Moritz; Oliva Valls, Sergi
no
Lower bounds, Pigeonhole principle
The relativized weak pigeonhole principle states that if at least 2n out of n2 pigeons fly into n holes, then some hole must be doubly occupied. We prove that every DNFrefutation of the CNF encoding of this principle requires size 2((log n)3/2ϵ) for every ε > 0 and every sufficiently large n. For its proof we need to discuss the existence of unbalanced lowdegree bipartite expanders satisfying a certain robustness condition.

Recolzament als nous estudiants del grau d’Enginyeria de sistemes TIC en l’EPSEM –UPC: la mentoria
http://hdl.handle.net/2117/22081
Title: Recolzament als nous estudiants del grau d’Enginyeria de sistemes TIC en l’EPSEM –UPC: la mentoria
Authors: Gorchs Altarriba, Roser; Molinero Albareda, Xavier
Abstract: Als estudiants de nou ingrés a l'Escola Politècnica Superior d'Enginyeria de Manresa (EPSEM) de la UPC se'ls proporciona voluntàriament
Fri, 14 Mar 2014 15:26:02 GMT
http://hdl.handle.net/2117/22081
20140314T15:26:02Z
Gorchs Altarriba, Roser; Molinero Albareda, Xavier
no
Mentoria, Estudis d'enginyeria, Estudiants de 1r curs universitari
Als estudiants de nou ingrés a l'Escola Politècnica Superior d'Enginyeria de Manresa (EPSEM) de la UPC se'ls proporciona voluntàriament

A fuzzybased trustworthiness system for P2P communications in JXTAoverlay considering positive and negative effects
http://hdl.handle.net/2117/21434
Title: A fuzzybased trustworthiness system for P2P communications in JXTAoverlay considering positive and negative effects
Authors: Umezaki, Kouhei; Spaho, Evjola; Barolli, Leonard; Ikeda, Makoto; Xhafa Xhafa, Fatos; Takizawa, Makoto
Abstract: In PeertoPeer (P2P) networks, peers often interact with unknown peers and finding a reliable peer for interaction is a major challenge. In our previous work, we proposed and implemented a fuzzybased trustworthiness system, which considered only positive effect parameters. In this paper, we propose a new fuzzybased trustworthiness system for P2P Communications in JXTAOverlay that decides the Peer Reliability (PR) considering three parameters: Number of Uploads (NU), Peer Disconnections (PD) and Reputation(R). In the proposed system, the NU and PD parameters have negative effect, while R parameter has positive effect for deciding peer reliability. We evaluate the proposed system by computer simulations. The simulation results has shown that the proposed system can effectively help peers to select reliable peers to download information.
Mon, 03 Feb 2014 14:11:01 GMT
http://hdl.handle.net/2117/21434
20140203T14:11:01Z
Umezaki, Kouhei; Spaho, Evjola; Barolli, Leonard; Ikeda, Makoto; Xhafa Xhafa, Fatos; Takizawa, Makoto
no
Fuzzy system, JXTAoverlay, P2P
In PeertoPeer (P2P) networks, peers often interact with unknown peers and finding a reliable peer for interaction is a major challenge. In our previous work, we proposed and implemented a fuzzybased trustworthiness system, which considered only positive effect parameters. In this paper, we propose a new fuzzybased trustworthiness system for P2P Communications in JXTAOverlay that decides the Peer Reliability (PR) considering three parameters: Number of Uploads (NU), Peer Disconnections (PD) and Reputation(R). In the proposed system, the NU and PD parameters have negative effect, while R parameter has positive effect for deciding peer reliability. We evaluate the proposed system by computer simulations. The simulation results has shown that the proposed system can effectively help peers to select reliable peers to download information.