ALBCOM - Algorismia, Bioinformàtica, Complexitat i Mètodes Formals
http://hdl.handle.net/2117/3092
2017-01-19T08:54:43ZFirefighting as a Game
http://hdl.handle.net/2117/99479
Firefighting as a Game
Álvarez Faura, M. del Carme; Blesa Aguilera, Maria Josep; Molter, Hendrik
The Firefighter Problem was proposed in 1995 [16] as a deterministic discrete-time model for the spread (and containment) of a fire. Its applications reach from real fires to the spreading of deseases and the containment of floods. Furthermore, it can be used to model the spread of computer viruses or viral marketing in communication networks. In this work, we study the problem from a game-theorical perspective. Such a context seems very appropriate when applied to large networks, where entities may act and make decisions based on their own interests, without global coordination. We model the Firefighter Problem as a strategic game where there is one player for each time step who decides where to place the firefighters. We show that the Price of Anarchy is linear in the general case, but at most 2 for trees. We prove that the quality of the equilibria improves when allowing coalitional cooperation among players. In general, we have that the Price of Anarchy is in O( n / k ) where k is the coalition size. Furthermore, we show that there are topologies which have a constant Price of Anarchy even when constant sized coalitions are considered.
2017-01-17T13:25:59ZÁlvarez Faura, M. del CarmeBlesa Aguilera, Maria JosepMolter, HendrikThe Firefighter Problem was proposed in 1995 [16] as a deterministic discrete-time model for the spread (and containment) of a fire. Its applications reach from real fires to the spreading of deseases and the containment of floods. Furthermore, it can be used to model the spread of computer viruses or viral marketing in communication networks. In this work, we study the problem from a game-theorical perspective. Such a context seems very appropriate when applied to large networks, where entities may act and make decisions based on their own interests, without global coordination. We model the Firefighter Problem as a strategic game where there is one player for each time step who decides where to place the firefighters. We show that the Price of Anarchy is linear in the general case, but at most 2 for trees. We prove that the quality of the equilibria improves when allowing coalitional cooperation among players. In general, we have that the Price of Anarchy is in O( n / k ) where k is the coalition size. Furthermore, we show that there are topologies which have a constant Price of Anarchy even when constant sized coalitions are considered.A graph-semantics of business configurations
http://hdl.handle.net/2117/99474
A graph-semantics of business configurations
Fiadeiro, José Luiz; Mylonakis Pascual, Nicolás; Orejas Valdés, Fernando
In this paper we give graph-semantics to a fundamental part of the semantics of the service modeling language SRML. To achieve this goal we develop a new graph transformation system for what we call 2-level symbolic graphs. These kind of graphs extend symbolic graphs with a simple 2-level hierarchy that can be generalized to arbitrary hierarchies. We formalize the semantics using this new graph transformation system using a simple example of a trip booking agent.
2017-01-17T13:16:27ZFiadeiro, José LuizMylonakis Pascual, NicolásOrejas Valdés, FernandoIn this paper we give graph-semantics to a fundamental part of the semantics of the service modeling language SRML. To achieve this goal we develop a new graph transformation system for what we call 2-level symbolic graphs. These kind of graphs extend symbolic graphs with a simple 2-level hierarchy that can be generalized to arbitrary hierarchies. We formalize the semantics using this new graph transformation system using a simple example of a trip booking agent.Hierarchical conformance checking of process models based on event logs
http://hdl.handle.net/2117/99402
Hierarchical conformance checking of process models based on event logs
Muñoz Gama, Jorge; Carmona Vargas, Josep; Aalst, Wil M.P. van der
Process mining techniques aim to extract knowledge from event logs. Conformance checking is one of the hard problems in process mining: it aims to diagnose and quantify the mismatch between observed and modeled behavior. Precise conformance checking implies solving complex optimization problems and is therefore computationally challenging for real-life event logs. In this paper a technique to apply hierarchical conformance checking is presented, based on a state-of-the-art algorithm for deriving the subprocesses structure underlying a process model. Hierarchical conformance checking allows us to decompose problems that would otherwise be intractable. Moreover, users can navigate through conformance results and zoom into parts of the model that have a poor conformance. The technique has been implemented as a ProM plugin and an experimental evaluation showing the signicance of the approach is provided.
2017-01-17T09:43:18ZMuñoz Gama, JorgeCarmona Vargas, JosepAalst, Wil M.P. van derProcess mining techniques aim to extract knowledge from event logs. Conformance checking is one of the hard problems in process mining: it aims to diagnose and quantify the mismatch between observed and modeled behavior. Precise conformance checking implies solving complex optimization problems and is therefore computationally challenging for real-life event logs. In this paper a technique to apply hierarchical conformance checking is presented, based on a state-of-the-art algorithm for deriving the subprocesses structure underlying a process model. Hierarchical conformance checking allows us to decompose problems that would otherwise be intractable. Moreover, users can navigate through conformance results and zoom into parts of the model that have a poor conformance. The technique has been implemented as a ProM plugin and an experimental evaluation showing the signicance of the approach is provided.Analysis of mesh router placement in wireless mesh networks using Friedman test
http://hdl.handle.net/2117/99332
Analysis of mesh router placement in wireless mesh networks using Friedman test
Oda, Tetsuya; Barolli, Admir; Spaho, Evjola; Barolli, Leonard; Xhafa Xhafa, Fatos
In this paper, we deal with connectivity and coverage problem in Wireless Mesh Networks (WMNs). We used Friedman test to compare Genetic Algorithm (GA) and Tabu Search (TS). We found out that GA and TS have difference in their performance. Then, we used the implemented systems WMN-GA and WMN-TS to evaluate and compare the performance of the system for different distributions of mesh clients in terms of giant component and covered mesh clients. The simulation results shows that for big radius of communication distances WMN-GA performs better than WMN-TS for Uniform, Normal and Weibull distributions of mesh clients. For Exponential distribution WMN-TS performs better than WMN-GA for all radius of communication distances.
(c) 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.
2017-01-16T15:28:45ZOda, TetsuyaBarolli, AdmirSpaho, EvjolaBarolli, LeonardXhafa Xhafa, FatosIn this paper, we deal with connectivity and coverage problem in Wireless Mesh Networks (WMNs). We used Friedman test to compare Genetic Algorithm (GA) and Tabu Search (TS). We found out that GA and TS have difference in their performance. Then, we used the implemented systems WMN-GA and WMN-TS to evaluate and compare the performance of the system for different distributions of mesh clients in terms of giant component and covered mesh clients. The simulation results shows that for big radius of communication distances WMN-GA performs better than WMN-TS for Uniform, Normal and Weibull distributions of mesh clients. For Exponential distribution WMN-TS performs better than WMN-GA for all radius of communication distances.A Tabu Search algorithm for ground station scheduling problem
http://hdl.handle.net/2117/99330
A Tabu Search algorithm for ground station scheduling problem
Xhafa Xhafa, Fatos; Herrero Garcia, Xavier; Barolli, Admir; Takizawa, Makoto
Mission planning plays an important role in satellite control systems. Satellites are not autonomously operated in many cases but are controlled by tele-commands transmitted from ground stations. Therefore, mission scheduling is crucial to efficient satellite control systems, especially with increase of number of satellites and more complex missions to be planned. In a general setting, the satellite mission scheduling consists in allocating tasks such as observation, communication, etc. to resources (spacecrafts (SCs), satellites, ground stations). One common version of this problem is that of ground station scheduling, in which the aim is to compute an optimal planning of communications between satellites and operations teams of Ground Station (GS). Because the communication between SCs and GSs can be done during specific window times, this problem can also be seen as a window time scheduling problem. The required communication time is usually quite smaller than the window of visibility of SCs to GSs, however, clashes are produced, making the problem highly constrained. In this paper we present a Tabu Search (TS) algorithm for the problem, while considering several objective functions, namely, windows fitness, clashes fitness, time requirement fitness, and resource usage fitness. The proposed algorithm is evaluated by a set of problem instances of varying size and complexity generated with the STK simulation toolkit. The computational results showed the efficacy of TS for solving the problem on all considered objectives.
(c) 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.
2017-01-16T15:19:33ZXhafa Xhafa, FatosHerrero Garcia, XavierBarolli, AdmirTakizawa, MakotoMission planning plays an important role in satellite control systems. Satellites are not autonomously operated in many cases but are controlled by tele-commands transmitted from ground stations. Therefore, mission scheduling is crucial to efficient satellite control systems, especially with increase of number of satellites and more complex missions to be planned. In a general setting, the satellite mission scheduling consists in allocating tasks such as observation, communication, etc. to resources (spacecrafts (SCs), satellites, ground stations). One common version of this problem is that of ground station scheduling, in which the aim is to compute an optimal planning of communications between satellites and operations teams of Ground Station (GS). Because the communication between SCs and GSs can be done during specific window times, this problem can also be seen as a window time scheduling problem. The required communication time is usually quite smaller than the window of visibility of SCs to GSs, however, clashes are produced, making the problem highly constrained. In this paper we present a Tabu Search (TS) algorithm for the problem, while considering several objective functions, namely, windows fitness, clashes fitness, time requirement fitness, and resource usage fitness. The proposed algorithm is evaluated by a set of problem instances of varying size and complexity generated with the STK simulation toolkit. The computational results showed the efficacy of TS for solving the problem on all considered objectives.Security in online learning assessment towards an effective trustworthiness approach to support e-learning teams
http://hdl.handle.net/2117/99050
Security in online learning assessment towards an effective trustworthiness approach to support e-learning teams
Miguel, Jorge; Caballé Llobet, Santiago; Xhafa Xhafa, Fatos; Prieto, Josep
This paper proposes a trustworthiness model for the design of secure learning assessment in on-line collaborative learning groups. Although computer supported collaborative learning has been widely adopted in many educational institutions over the last decade, there exist still drawbacks which limit their potential in collaborative learning activities. Among these limitations, we investigate information security requirements in on-line assessment, (e-assessment), which can be developed in collaborative learning contexts. Despite information security enhancements have been developed in recent years, to the best of our knowledge, integrated and holistic security models have not been completely carried out yet. Even when security advanced methodologies and technologies are deployed in Learning Management Systems, too many types of vulnerabilities still remain opened and unsolved. Therefore, new models such as trustworthiness approaches can overcome these lacks and support e-assessment requirements for e-Learning. To this end, a trustworthiness model is designed in order to conduct the guidelines of a holistic security model for on-line collaborative learning through effective trustworthiness approaches. In addition, since users' trustworthiness analysis involves large amounts of ill-structured data, a parallel processing paradigm is proposed to build relevant information modeling trustworthiness levels for e-Learning.
(c) 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.
2017-01-11T16:50:04ZMiguel, JorgeCaballé Llobet, SantiagoXhafa Xhafa, FatosPrieto, JosepThis paper proposes a trustworthiness model for the design of secure learning assessment in on-line collaborative learning groups. Although computer supported collaborative learning has been widely adopted in many educational institutions over the last decade, there exist still drawbacks which limit their potential in collaborative learning activities. Among these limitations, we investigate information security requirements in on-line assessment, (e-assessment), which can be developed in collaborative learning contexts. Despite information security enhancements have been developed in recent years, to the best of our knowledge, integrated and holistic security models have not been completely carried out yet. Even when security advanced methodologies and technologies are deployed in Learning Management Systems, too many types of vulnerabilities still remain opened and unsolved. Therefore, new models such as trustworthiness approaches can overcome these lacks and support e-assessment requirements for e-Learning. To this end, a trustworthiness model is designed in order to conduct the guidelines of a holistic security model for on-line collaborative learning through effective trustworthiness approaches. In addition, since users' trustworthiness analysis involves large amounts of ill-structured data, a parallel processing paradigm is proposed to build relevant information modeling trustworthiness levels for e-Learning.Celebrity games
http://hdl.handle.net/2117/98737
Celebrity games
Álvarez Faura, M. del Carme; Blesa Aguilera, Maria Josep; Duch Brown, Amalia; Messegué Buisan, Arnau; Serna Iglesias, María José
We introduce Celebrity games, a new model of network creation games. In this model players have weights (W being the sum of all the player's weights) and there is a critical distance ß as well as a link cost a. The cost incurred by a player depends on the cost of establishing links to other players and on the sum of the weights of those players that remain farther than the critical distance. Intuitively, the aim of any player is to be relatively close (at a distance less than ß ) from the rest of players, mainly of those having high weights. The main features of celebrity games are that: computing the best response of a player is NP-hard if ß>1 and polynomial time solvable otherwise; they always have a pure Nash equilibrium; the family of celebrity games having a connected Nash equilibrium is characterized (the so called star celebrity games) and bounds on the diameter of the resulting equilibrium graphs are given; a special case of star celebrity games shares its set of Nash equilibrium profiles with the MaxBD games with uniform bounded distance ß introduced in Bilò et al. [6]. Moreover, we analyze the Price of Anarchy (PoA) and of Stability (PoS) of celebrity games and give several bounds. These are that: for non-star celebrity games PoA=PoS=max{1,W/a}; for star celebrity games PoS=1 and PoA=O(min{n/ß,Wa}) but if the Nash Equilibrium is a tree then the PoA is O(1); finally, when ß=1 the PoA is at most 2. The upper bounds on the PoA are complemented with some lower bounds for ß=2.
2016-12-22T07:35:11ZÁlvarez Faura, M. del CarmeBlesa Aguilera, Maria JosepDuch Brown, AmaliaMessegué Buisan, ArnauSerna Iglesias, María JoséWe introduce Celebrity games, a new model of network creation games. In this model players have weights (W being the sum of all the player's weights) and there is a critical distance ß as well as a link cost a. The cost incurred by a player depends on the cost of establishing links to other players and on the sum of the weights of those players that remain farther than the critical distance. Intuitively, the aim of any player is to be relatively close (at a distance less than ß ) from the rest of players, mainly of those having high weights. The main features of celebrity games are that: computing the best response of a player is NP-hard if ß>1 and polynomial time solvable otherwise; they always have a pure Nash equilibrium; the family of celebrity games having a connected Nash equilibrium is characterized (the so called star celebrity games) and bounds on the diameter of the resulting equilibrium graphs are given; a special case of star celebrity games shares its set of Nash equilibrium profiles with the MaxBD games with uniform bounded distance ß introduced in Bilò et al. [6]. Moreover, we analyze the Price of Anarchy (PoA) and of Stability (PoS) of celebrity games and give several bounds. These are that: for non-star celebrity games PoA=PoS=max{1,W/a}; for star celebrity games PoS=1 and PoA=O(min{n/ß,Wa}) but if the Nash Equilibrium is a tree then the PoA is O(1); finally, when ß=1 the PoA is at most 2. The upper bounds on the PoA are complemented with some lower bounds for ß=2.Network formation for asymmetric players and bilateral contracting
http://hdl.handle.net/2117/98314
Network formation for asymmetric players and bilateral contracting
Álvarez Faura, M. del Carme; Serna Iglesias, María José; Fernández, Aleix
We study a network formation game where players wish to send traffic to other players. Players can be seen as nodes of an undirected graph whose edges are defined by contracts between the corresponding players. Each player can contract bilaterally with others to form bidirectional links or break unilaterally contracts to eliminate the corresponding links. Our model is an extension of the traffic routing model considered in Arcaute, E., Johari, R., Mannor, S., (IEEE Trans. Automat. Contr. 54(8), 1765–1778 2009) in which we do not require the traffic to be uniform and all-to-all. Player i specifies the amount of traffic tij = 0 that wants to send to player j. Our notion of stability is the network pairwise Nash stability, when no node wishes to deviate unilaterally and no pair of nodes can obtain benefit from deviating bilaterally. We show a characterization of the topologies that are pairwise Nash stable for a given traffic matrix. We prove that the best response problem is NP-hard and devise a myopic dynamics so that the deviation of the active node can be computed in polynomial time. We show the convergence of the dynamics to pairwise Nash configurations, when the contracting functions are anti-symmetric and affine, and that the expected convergence time is polynomial in the number of nodes when the node activation process is uniform.
2016-12-15T09:45:05ZÁlvarez Faura, M. del CarmeSerna Iglesias, María JoséFernández, AleixWe study a network formation game where players wish to send traffic to other players. Players can be seen as nodes of an undirected graph whose edges are defined by contracts between the corresponding players. Each player can contract bilaterally with others to form bidirectional links or break unilaterally contracts to eliminate the corresponding links. Our model is an extension of the traffic routing model considered in Arcaute, E., Johari, R., Mannor, S., (IEEE Trans. Automat. Contr. 54(8), 1765–1778 2009) in which we do not require the traffic to be uniform and all-to-all. Player i specifies the amount of traffic tij = 0 that wants to send to player j. Our notion of stability is the network pairwise Nash stability, when no node wishes to deviate unilaterally and no pair of nodes can obtain benefit from deviating bilaterally. We show a characterization of the topologies that are pairwise Nash stable for a given traffic matrix. We prove that the best response problem is NP-hard and devise a myopic dynamics so that the deviation of the active node can be computed in polynomial time. We show the convergence of the dynamics to pairwise Nash configurations, when the contracting functions are anti-symmetric and affine, and that the expected convergence time is polynomial in the number of nodes when the node activation process is uniform.Fringe analysis of synchronized parallel algorithms on 2--3 trees
http://hdl.handle.net/2117/98212
Fringe analysis of synchronized parallel algorithms on 2--3 trees
Baeza-Yates, R; Gabarró Vallès, Joaquim; Messeguer Peypoch, Xavier
We are interested in the fringe analysis of synchronized parallel insertion algorithms on 2—3 trees namely the algorithm of W.Paul
U. Vishkin and H. Wagener PVW. This algorithm inserts k keys into
a tree of size n with parallel time Olog n log k
Fringe analysis studies the distribution of the bottom subtrees and it is
still an open problem for parallel algorithms on search trees. To tackle
this problem we introduce a new kind of algorithms whose two extreme
cases seems to upper and lower bounds the performance of the PVW
algorithm.
We extend the fringe analysis to parallel algorithms and we get a rich
mathematical structure giving new interpretations even in the sequential
case. The process of insertions is modeled by a Markov chain and the
coecients of the transition matrix are related with the expected local
behavior of our algorithm. Finally we show that this matrix has a power
expansion over (n+1)-1 where the coecients are the binomial transform
of the expected local behavior. This expansion shows that the parallel
case can be approximated by iterating the sequential case.
2016-12-14T13:10:05ZBaeza-Yates, RGabarró Vallès, JoaquimMesseguer Peypoch, XavierWe are interested in the fringe analysis of synchronized parallel insertion algorithms on 2—3 trees namely the algorithm of W.Paul
U. Vishkin and H. Wagener PVW. This algorithm inserts k keys into
a tree of size n with parallel time Olog n log k
Fringe analysis studies the distribution of the bottom subtrees and it is
still an open problem for parallel algorithms on search trees. To tackle
this problem we introduce a new kind of algorithms whose two extreme
cases seems to upper and lower bounds the performance of the PVW
algorithm.
We extend the fringe analysis to parallel algorithms and we get a rich
mathematical structure giving new interpretations even in the sequential
case. The process of insertions is modeled by a Markov chain and the
coecients of the transition matrix are related with the expected local
behavior of our algorithm. Finally we show that this matrix has a power
expansion over (n+1)-1 where the coecients are the binomial transform
of the expected local behavior. This expansion shows that the parallel
case can be approximated by iterating the sequential case.Dimension and codimension of simple games
http://hdl.handle.net/2117/97660
Dimension and codimension of simple games
Kurz, Sascha; Molinero Albareda, Xavier; Olsen, Martin; Serna Iglesias, María José
This paper studies the complexity of computing a representation of a simple game as the intersection (union) of weighted majority games, as well as, the dimension or the codimension. We also present some examples with linear dimension and exponential codimension with respect to the number of players.
2016-12-01T18:56:01ZKurz, SaschaMolinero Albareda, XavierOlsen, MartinSerna Iglesias, María JoséThis paper studies the complexity of computing a representation of a simple game as the intersection (union) of weighted majority games, as well as, the dimension or the codimension. We also present some examples with linear dimension and exponential codimension with respect to the number of players.