Reports de recerca
http://hdl.handle.net/2117/3094
2016-07-24T10:54:21ZProcess mining meets abstract interpretation
http://hdl.handle.net/2117/88077
Process mining meets abstract interpretation
Carmona Vargas, Josep; Cortadella Fortuny, Jordi
The discovery of process models out of system traces is an interesting problem that has received significant attention in the last years. In this work, a theory for the derivation of a Petri net from a set of traces is presented. The method is based on the theory of abstract interpretation, which has been applied successfully in other areas. The principal application of the theory presented is Process Mining, an area that tries to incorporate the use of formal models both in the design and use of information systems.
2016-06-16T08:50:11ZCarmona Vargas, JosepCortadella Fortuny, JordiThe discovery of process models out of system traces is an interesting problem that has received significant attention in the last years. In this work, a theory for the derivation of a Petri net from a set of traces is presented. The method is based on the theory of abstract interpretation, which has been applied successfully in other areas. The principal application of the theory presented is Process Mining, an area that tries to incorporate the use of formal models both in the design and use of information systems.Process mining from a basis of state regions
http://hdl.handle.net/2117/88012
Process mining from a basis of state regions
Solé, Marc; Carmona Vargas, Josep
A central problem in the area of Process Mining is to obtain a formal model that represents selected behavior of a system. The theory of regions has been applied to address this problem, enabling the derivation of a Petri net whose language includes a set of traces. However, when dealing with real-life systems, the available tool support for performing such task is unsatisfactory, due to the complex algorithms that are required. In this paper, the theory of regions is revisited to devise a novel technique that explores the space of regions by combining the elements of a region basis. Due to its light space requirements, the approach can represent an important step for bridging the gap between the theory of regions and its industrial application. Experimental results improve in orders of magnitude state-of-the-art tools for the same task.
2016-06-15T07:59:02ZSolé, MarcCarmona Vargas, JosepA central problem in the area of Process Mining is to obtain a formal model that represents selected behavior of a system. The theory of regions has been applied to address this problem, enabling the derivation of a Petri net whose language includes a set of traces. However, when dealing with real-life systems, the available tool support for performing such task is unsatisfactory, due to the complex algorithms that are required. In this paper, the theory of regions is revisited to devise a novel technique that explores the space of regions by combining the elements of a region basis. Due to its light space requirements, the approach can represent an important step for bridging the gap between the theory of regions and its industrial application. Experimental results improve in orders of magnitude state-of-the-art tools for the same task.Multikey Quickselect
http://hdl.handle.net/2117/88009
Multikey Quickselect
Frias Moya, Leonor; Roura Ferret, Salvador
In this paper we introduce Multikey Quickselect: an efficient, in-place, and easy to implement algorithm for the selection problem for strings. We present several variants of our basic algorithm, which apply to two different flavors of the selection problem. Also, we analyze the cost of the main variants, measured as the expected number of character comparisons and elements swaps. Some of the enhancements presented in this paper apply to Multikey Quicksort as well.
2016-06-15T07:21:39ZFrias Moya, LeonorRoura Ferret, SalvadorIn this paper we introduce Multikey Quickselect: an efficient, in-place, and easy to implement algorithm for the selection problem for strings. We present several variants of our basic algorithm, which apply to two different flavors of the selection problem. Also, we analyze the cost of the main variants, measured as the expected number of character comparisons and elements swaps. Some of the enhancements presented in this paper apply to Multikey Quicksort as well.The HOM problem is decidable
http://hdl.handle.net/2117/87972
The HOM problem is decidable
Godoy, Guillem; Giménez, Omer; Ramos Garrido, Lander; Álvarez Faura, M. del Carme
We close affirmatively a question which has been open for 35 years: decidability of the HOM problem. The HOM problem consists in deciding, given a tree homomorphism $H$ and a regular tree languagle $L$ represented by a tree automaton, whether $H(L)$ is regular. For deciding the HOM problem, we develop new constructions and techniques which are interesting by themselves, and provide several significant intermediate results. For example, we prove that the universality problem is decidable for languages represented by tree automata with equality constraints, and that the equivalence and inclusion problems are decidable for images of regular languages through tree homomorphisms. Our contributions are based on the following new results. We describe a simple transformation for converting a tree automaton with equality constraints into a tree automaton with disequality constraints recognizing the complementary language. We also define a new class of automaton with arbitrary disequality constraints and a particular kind of equality constraints. This new class essentially recognizes the intersection of a tree automaton with disequality constraints and the image of a regular language through a tree homomorphism. We prove decidability of emptiness and finiteness for this class by a pumping mechanism. The above constructions are combined adequately to provide an algorithm deciding the HOM problem.
2016-06-14T11:51:17ZGodoy, GuillemGiménez, OmerRamos Garrido, LanderÁlvarez Faura, M. del CarmeWe close affirmatively a question which has been open for 35 years: decidability of the HOM problem. The HOM problem consists in deciding, given a tree homomorphism $H$ and a regular tree languagle $L$ represented by a tree automaton, whether $H(L)$ is regular. For deciding the HOM problem, we develop new constructions and techniques which are interesting by themselves, and provide several significant intermediate results. For example, we prove that the universality problem is decidable for languages represented by tree automata with equality constraints, and that the equivalence and inclusion problems are decidable for images of regular languages through tree homomorphisms. Our contributions are based on the following new results. We describe a simple transformation for converting a tree automaton with equality constraints into a tree automaton with disequality constraints recognizing the complementary language. We also define a new class of automaton with arbitrary disequality constraints and a particular kind of equality constraints. This new class essentially recognizes the intersection of a tree automaton with disequality constraints and the image of a regular language through a tree homomorphism. We prove decidability of emptiness and finiteness for this class by a pumping mechanism. The above constructions are combined adequately to provide an algorithm deciding the HOM problem.Speculation in elastic systems
http://hdl.handle.net/2117/87919
Speculation in elastic systems
Galcerán Oms, Marc; Cortadella Fortuny, Jordi; Kishinevsky, Mike
Speculation is a well-known technique for increasing parallelism of the microprocessor pipelines and hence their performance. While implementing speculation in modern design practice is error-prone
and mostly ad-hoc, this paper proposes a correct-by-construction method for implementing speculation in Elastic Systems. The technique is based on applying provably correct transformations such as early
evaluation, insertion of anti-tokens and bubbles, retiming, and sharing. It allows to explore different micro-architectural solutions for better design trade-offs. The benefits of speculation are illustrated with
two examples in which these transformations are systematically applied. The method proposed in this paper is amenable for automation in a synthesis flow.
2016-06-13T09:35:08ZGalcerán Oms, MarcCortadella Fortuny, JordiKishinevsky, MikeSpeculation is a well-known technique for increasing parallelism of the microprocessor pipelines and hence their performance. While implementing speculation in modern design practice is error-prone
and mostly ad-hoc, this paper proposes a correct-by-construction method for implementing speculation in Elastic Systems. The technique is based on applying provably correct transformations such as early
evaluation, insertion of anti-tokens and bubbles, retiming, and sharing. It allows to explore different micro-architectural solutions for better design trade-offs. The benefits of speculation are illustrated with
two examples in which these transformations are systematically applied. The method proposed in this paper is amenable for automation in a synthesis flow.Retiming and recycling for elastic systems with early evaluation
http://hdl.handle.net/2117/87917
Retiming and recycling for elastic systems with early evaluation
Bufistov, Dmitry; Cortadella Fortuny, Jordi; Galcerán Oms, Marc; Julvez Bueno, Jorge Emilio; Kishinevsky, Mike
Retiming and recycling are two transformations used to optimize the performance of latency-insensitive (a.k.a. synchronous elastic) systems. This paper presents an approach that combines these two transformations for performance optimization of elastic systems with early evaluation. The method is based on Mixed Integer Linear Programming. On a set of random benchmarks the proposed method achieves, in average, 14.5% performance improvement over min-delay retiming configurations.
2016-06-13T08:59:50ZBufistov, DmitryCortadella Fortuny, JordiGalcerán Oms, MarcJulvez Bueno, Jorge EmilioKishinevsky, MikeRetiming and recycling are two transformations used to optimize the performance of latency-insensitive (a.k.a. synchronous elastic) systems. This paper presents an approach that combines these two transformations for performance optimization of elastic systems with early evaluation. The method is based on Mixed Integer Linear Programming. On a set of random benchmarks the proposed method achieves, in average, 14.5% performance improvement over min-delay retiming configurations.Divide-and-conquer strategies for process mining
http://hdl.handle.net/2117/87625
Divide-and-conquer strategies for process mining
Carmona Vargas, Josep; Cortadella Fortuny, Jordi; Kishinevsky, Mike
The main goal of Process Mining is to extract process models from logs of a system. Among the possible models to represent a process, Petri nets is an ideal candidate due to its graphical representation, clear semantics and expressive p ower. The theory of regions can be used to transform a log into a Petri net, but unfortunately the transformation requires algorithms with high complexity. This paper provides techniques to overcome this limitation. Either by using decomposition techniques, or by clustering events in the log and working on projections, the proposed techniques can be used to alleviat e the complexity and make the theory of regions practical for real-life problems.
A previous version of this report was titled "A recursive approach for Process Mining"
2016-06-02T07:43:25ZCarmona Vargas, JosepCortadella Fortuny, JordiKishinevsky, MikeThe main goal of Process Mining is to extract process models from logs of a system. Among the possible models to represent a process, Petri nets is an ideal candidate due to its graphical representation, clear semantics and expressive p ower. The theory of regions can be used to transform a log into a Petri net, but unfortunately the transformation requires algorithms with high complexity. This paper provides techniques to overcome this limitation. Either by using decomposition techniques, or by clustering events in the log and working on projections, the proposed techniques can be used to alleviat e the complexity and make the theory of regions practical for real-life problems.Analysis of the strategy "Hiring above the alpha-quantile"
http://hdl.handle.net/2117/87542
Analysis of the strategy "Hiring above the alpha-quantile"
Helmiy, Ahmed; Martínez Parra, Conrado; Panholzer, Alois
We study here the strategy hiring above the α-quantile of the hired staﬀ. This strategy was introduced ﬁrst by Archibald and Martınez in 2009. We show here more results like lower and upper bounds for many interesting quantities for the general case, i.e., 0 < alpha < 1. For the main parameter, number of hired candidates, we were able to obtain the exact and limiting distributions for alpha = 1/d, with d a positive integer.
2016-05-31T11:53:08ZHelmiy, AhmedMartínez Parra, ConradoPanholzer, AloisWe study here the strategy hiring above the α-quantile of the hired staﬀ. This strategy was introduced ﬁrst by Archibald and Martınez in 2009. We show here more results like lower and upper bounds for many interesting quantities for the general case, i.e., 0 < alpha < 1. For the main parameter, number of hired candidates, we were able to obtain the exact and limiting distributions for alpha = 1/d, with d a positive integer.A review on DISC 2005, the 19th International Symposium on Distributed Computing
http://hdl.handle.net/2117/87343
A review on DISC 2005, the 19th International Symposium on Distributed Computing
Blesa Aguilera, Maria Josep; Georgiou, Chryssis
DISC is an international symposium on the theory, design, analysis, implementation and application of distributed systems and networks. The well-known International Symposium on Distributed Computing is organized annually in cooperation with the European Association for Theoretical Computer Science (EATCS). This is a review on the 19th International Symposium on Distributed Computing, which took place in Kraków, Poland, on September 26--29, 2005. The proceedings of DISC 2005 are published by Springer, as volume 3724 of the Lecture Notes in Computer Science (LNCS) series. The conference website can be found at www.mimuw.edu.pl/~disc2005.
2016-05-26T08:10:28ZBlesa Aguilera, Maria JosepGeorgiou, ChryssisDISC is an international symposium on the theory, design, analysis, implementation and application of distributed systems and networks. The well-known International Symposium on Distributed Computing is organized annually in cooperation with the European Association for Theoretical Computer Science (EATCS). This is a review on the 19th International Symposium on Distributed Computing, which took place in Kraków, Poland, on September 26--29, 2005. The proceedings of DISC 2005 are published by Springer, as volume 3724 of the Lecture Notes in Computer Science (LNCS) series. The conference website can be found at www.mimuw.edu.pl/~disc2005.An algebraic view of the relation between largest common subtrees and smallest common supertrees
http://hdl.handle.net/2117/87254
An algebraic view of the relation between largest common subtrees and smallest common supertrees
Rosselló, Francesc; Valiente Feruglio, Gabriel Alejandro
The relationship between two important problems in tree pattern matching, the largest common subtree and the smallest common supertree of two trees, is established by means of simple constructions, which allow one to obtain the largest common subtree from the smallest common supertree, and vice versa. These constructions are given for the problems of isomorphic, homeomorphic, topological, and minor embeddings. They can be implemented by a straightforward extension of any algorithm that solves one of the two problems, and the extension only takes time linear in the size of the trees.
2016-05-24T07:04:02ZRosselló, FrancescValiente Feruglio, Gabriel AlejandroThe relationship between two important problems in tree pattern matching, the largest common subtree and the smallest common supertree of two trees, is established by means of simple constructions, which allow one to obtain the largest common subtree from the smallest common supertree, and vice versa. These constructions are given for the problems of isomorphic, homeomorphic, topological, and minor embeddings. They can be implemented by a straightforward extension of any algorithm that solves one of the two problems, and the extension only takes time linear in the size of the trees.