Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3095
20161210T08:58:30Z

Ring oscillator clocks and margins
http://hdl.handle.net/2117/96481
Ring oscillator clocks and margins
Cortadella Fortuny, Jordi; Lupon Navazo, Marc; Moreno Vega, Alberto; Roca Pérez, Antoni; Sapatnekar, Sachin
How much margin do we have to add to the delay lines of a bundleddata circuit? This paper is an attempt to give a methodical answer to this question, taking into account all sources of variability and the existing EDA machinery for timing analysis and signoff. The paper is based on the study of the margins of a ring oscillator that substitutes a PLL as clock generator. A timing model is proposed that shows that a 12% margin for delay lines can be sufficient to cover variability in a 65nm technology. In a typical scenario, performance and energy improvements between 15% and 35% can be obtained by using a ring oscillator instead of a PLL. The paper concludes that a synchronous circuit with a ring oscillator clock shows similar benefits in performance and energy as those of bundleddata asynchronous circuits.
20161110T12:52:04Z
Cortadella Fortuny, Jordi
Lupon Navazo, Marc
Moreno Vega, Alberto
Roca Pérez, Antoni
Sapatnekar, Sachin
How much margin do we have to add to the delay lines of a bundleddata circuit? This paper is an attempt to give a methodical answer to this question, taking into account all sources of variability and the existing EDA machinery for timing analysis and signoff. The paper is based on the study of the margins of a ring oscillator that substitutes a PLL as clock generator. A timing model is proposed that shows that a 12% margin for delay lines can be sufficient to cover variability in a 65nm technology. In a typical scenario, performance and energy improvements between 15% and 35% can be obtained by using a ring oscillator instead of a PLL. The paper concludes that a synchronous circuit with a ring oscillator clock shows similar benefits in performance and energy as those of bundleddata asynchronous circuits.

Discovering duplicate tasks in transition systems for the simplification of process models
http://hdl.handle.net/2117/96477
Discovering duplicate tasks in transition systems for the simplification of process models
San Pedro Martín, Javier de; Cortadella Fortuny, Jordi
This work presents a set of methods to improve the understandability of process models. Traditionally, simplification methods trade off quality metrics, such as fitness or precision. Conversely, the methods proposed in this paper produce simplified models while preserving or even increasing fidelity metrics. The first problem addressed in the
paper is the discovery of duplicate tasks. A new method is proposed that avoids overfitting by working on the transition system generated by the log. The method is able to discover duplicate tasks even in the presence of concurrency and choice. The second problem is the structural simplification of the model by identifying optional and repetitive tasks. The tasks are substituted by annotated events that allow the removal of silent tasks and reduce the complexity of the
model. An important feature of the methods proposed in this paper is that they are independent from the actual miner used for process discovery.
20161110T12:22:48Z
San Pedro Martín, Javier de
Cortadella Fortuny, Jordi
This work presents a set of methods to improve the understandability of process models. Traditionally, simplification methods trade off quality metrics, such as fitness or precision. Conversely, the methods proposed in this paper produce simplified models while preserving or even increasing fidelity metrics. The first problem addressed in the
paper is the discovery of duplicate tasks. A new method is proposed that avoids overfitting by working on the transition system generated by the log. The method is able to discover duplicate tasks even in the presence of concurrency and choice. The second problem is the structural simplification of the model by identifying optional and repetitive tasks. The tasks are substituted by annotated events that allow the removal of silent tasks and reduce the complexity of the
model. An important feature of the methods proposed in this paper is that they are independent from the actual miner used for process discovery.

MapReduce vs. pipelining counting triangles
http://hdl.handle.net/2117/90688
MapReduce vs. pipelining counting triangles
Pasarella Sánchez, Ana Edelmira; Vidal Serodio, Maria Esther; Zoltan, Cristina
In this paper we follow an alternative approach named pipeline, to implement a parallel implementation of the wellknown problem of counting triangles in a graph. This problem is especially interesting either when the input graph does not fit in memory or is dynamically generated. To be concrete, we implement a dynamic pipeline of processes and an adhoc MapReduce version using the language Go. We explote the ability of Go language to deal with channels and spawned processes. An empirical evaluation is conducted on graphs of different size and density. Observed results suggest that pipeline allows for the implementation of an efficient solution of the problem of counting triangles in a graph, particularly, in dense and large graphs, drastically reducing the execution time with respect to the MapReduce implementation.
20161011T11:41:38Z
Pasarella Sánchez, Ana Edelmira
Vidal Serodio, Maria Esther
Zoltan, Cristina
In this paper we follow an alternative approach named pipeline, to implement a parallel implementation of the wellknown problem of counting triangles in a graph. This problem is especially interesting either when the input graph does not fit in memory or is dynamically generated. To be concrete, we implement a dynamic pipeline of processes and an adhoc MapReduce version using the language Go. We explote the ability of Go language to deal with channels and spawned processes. An empirical evaluation is conducted on graphs of different size and density. Observed results suggest that pipeline allows for the implementation of an efficient solution of the problem of counting triangles in a graph, particularly, in dense and large graphs, drastically reducing the execution time with respect to the MapReduce implementation.

Securitysensitive tackling of obstructed workflow executions
http://hdl.handle.net/2117/90247
Securitysensitive tackling of obstructed workflow executions
Holderer, Julius; Carmona Vargas, Josep; Müller, Günter
Imposing access control onto workflows considerably reduces the set of users authorized to execute the workflow tasks. Further constraints (e.g. Separation of Duties) as well as unexpected unavailabilty of users may finally obstruct the successful workflow execution. To still complete the execution of an obstructed workflow, we envisage a hybrid
approach. If a log is provided, we partition its traces into “successful” and “obstructed” ones by analysing the given workflow and its authorizations. An obstruction should then be solved by finding its nearest match from the list of successful traces. If no log is provided, we flatten the workflow and its authorizations into a Petri net and encode the obstruction with a corresponding “obstruction marking”. The structural theory of Petri nets shall then be tweaked to provide a minimized Parikh vector, that may violate given firing rules, however reach a complete marking and by that, complete the workflow.
20160928T08:32:00Z
Holderer, Julius
Carmona Vargas, Josep
Müller, Günter
Imposing access control onto workflows considerably reduces the set of users authorized to execute the workflow tasks. Further constraints (e.g. Separation of Duties) as well as unexpected unavailabilty of users may finally obstruct the successful workflow execution. To still complete the execution of an obstructed workflow, we envisage a hybrid
approach. If a log is provided, we partition its traces into “successful” and “obstructed” ones by analysing the given workflow and its authorizations. An obstruction should then be solved by finding its nearest match from the list of successful traces. If no log is provided, we flatten the workflow and its authorizations into a Petri net and encode the obstruction with a corresponding “obstruction marking”. The structural theory of Petri nets shall then be tweaked to provide a minimized Parikh vector, that may violate given firing rules, however reach a complete marking and by that, complete the workflow.

De Menos a Distinto: Estudio de la Implantación de R en las asignaturas del grado de estadística
http://hdl.handle.net/2117/89582
De Menos a Distinto: Estudio de la Implantación de R en las asignaturas del grado de estadística
Baixeries i Juvillà, Jaume; Fairén González, Marta; Gabarró Vallès, Joaquim; Pasarella Sánchez, Ana Edelmira
Teaching computer science in degrees that are not computer science related presents an important challenge: to motivate the students and to achieve good average grades. The student’s complaint is always based on his lack of motivation: What is this subject useful for? and this is specially relevant when this subject is not easy to learn by the student. In this paper we show the case of computer courses in the Statistics degree taught in the Universitat de Barcelona (UB) and the Universitat Politècnica de Catalunya (UPC) (two Catalan universities). We initially tried to reduce the complexity of their contents in order to obtain better average grades. Yet, it did not workout as expected. Therefore, we changed our strategy and instead of making the contents easier (less complex), we changed the tools that were used to teach and tried to adapt them to the students’ interests. In this particular case, we decided to use the R programming language, a language widely used by statisticians, in order to explain the basics of programming. Therefore, we changed our strategy from less (simpler contents) to different (more elaborated and nontrivial contents adapted to meet their expectations).
20160905T15:19:46Z
Baixeries i Juvillà, Jaume
Fairén González, Marta
Gabarró Vallès, Joaquim
Pasarella Sánchez, Ana Edelmira
Teaching computer science in degrees that are not computer science related presents an important challenge: to motivate the students and to achieve good average grades. The student’s complaint is always based on his lack of motivation: What is this subject useful for? and this is specially relevant when this subject is not easy to learn by the student. In this paper we show the case of computer courses in the Statistics degree taught in the Universitat de Barcelona (UB) and the Universitat Politècnica de Catalunya (UPC) (two Catalan universities). We initially tried to reduce the complexity of their contents in order to obtain better average grades. Yet, it did not workout as expected. Therefore, we changed our strategy and instead of making the contents easier (less complex), we changed the tools that were used to teach and tried to adapt them to the students’ interests. In this particular case, we decided to use the R programming language, a language widely used by statisticians, in order to explain the basics of programming. Therefore, we changed our strategy from less (simpler contents) to different (more elaborated and nontrivial contents adapted to meet their expectations).

Incorporating negative information in process discovery
http://hdl.handle.net/2117/87175
Incorporating negative information in process discovery
Ponce de León, Hernán; Carmona Vargas, Josep; vanden Broucke, Seppe
The discovery of a formal process model from event logs describing real process executions is a challenging problem that has been studied from several angles. Most of the contributions consider the extraction of a model as a semisupervised problem where only positive information is available. In this paper we present a fresh look at process discovery where also negative information can be taken into account. This feature may be crucial for deriving process models which are not only simple, fitting and precise, but also good on generalizing the right behavior underlying an event log. The technique is based on numerical abstract domains and Satisfiability Modulo Theories (SMT), and can be combined with any process discovery technique. As an example, we show in detail how to supervise a recent technique that uses numerical abstract domains. Experiments performed in our prototype implementation show the effectiveness of the techniques and the ability to improve the results produced by selected discovery techniques.
20160519T07:46:54Z
Ponce de León, Hernán
Carmona Vargas, Josep
vanden Broucke, Seppe
The discovery of a formal process model from event logs describing real process executions is a challenging problem that has been studied from several angles. Most of the contributions consider the extraction of a model as a semisupervised problem where only positive information is available. In this paper we present a fresh look at process discovery where also negative information can be taken into account. This feature may be crucial for deriving process models which are not only simple, fitting and precise, but also good on generalizing the right behavior underlying an event log. The technique is based on numerical abstract domains and Satisfiability Modulo Theories (SMT), and can be combined with any process discovery technique. As an example, we show in detail how to supervise a recent technique that uses numerical abstract domains. Experiments performed in our prototype implementation show the effectiveness of the techniques and the ability to improve the results produced by selected discovery techniques.

Logbased simplification of process models
http://hdl.handle.net/2117/87035
Logbased simplification of process models
San Pedro Martín, Javier de; Carmona Vargas, Josep; Cortadella Fortuny, Jordi
The visualization of models is essential for userfriendly humanmachine interactions during Process Mining. A simple graphical representation contributes to give intuitive information about the behavior of a system. However, complex systems cannot always be represented with succinct models that can be easily visualized. Qualitypreserving model simplifications can be of paramount importance to alleviate the complexity of finding useful and attractive visualizations.
This paper presents a collection of logbased techniques to simplify process models. The techniques trade off visualfriendly properties with quality metrics related to logs, such as fitness and precision, to avoid degrading the resulting model. The algorithms, either cast as optimization problems or heuristically guided, find simplified versions of the initial process model, and can be applied in the final stage of the process mining lifecycle, between the discovery of a process model and the deployment to the final user. A tool has been developed and tested on large logs, producing simplified process models that are one order of magnitude smaller while keeping fitness and precision under reasonable margins.
20160513T08:52:34Z
San Pedro Martín, Javier de
Carmona Vargas, Josep
Cortadella Fortuny, Jordi
The visualization of models is essential for userfriendly humanmachine interactions during Process Mining. A simple graphical representation contributes to give intuitive information about the behavior of a system. However, complex systems cannot always be represented with succinct models that can be easily visualized. Qualitypreserving model simplifications can be of paramount importance to alleviate the complexity of finding useful and attractive visualizations.
This paper presents a collection of logbased techniques to simplify process models. The techniques trade off visualfriendly properties with quality metrics related to logs, such as fitness and precision, to avoid degrading the resulting model. The algorithms, either cast as optimization problems or heuristically guided, find simplified versions of the initial process model, and can be applied in the final stage of the process mining lifecycle, between the discovery of a process model and the deployment to the final user. A tool has been developed and tested on large logs, producing simplified process models that are one order of magnitude smaller while keeping fitness and precision under reasonable margins.

Can frogs find large independent sets in a decentralized way? Yes they can!
http://hdl.handle.net/2117/85203
Can frogs find large independent sets in a decentralized way? Yes they can!
Blum, Christian; Blesa Aguilera, Maria Josep; Calvo, Borja
The problem of identifying a maximal independent (node) set in a given graph is a fundamental problem in distributed computing. It has numerous applications, for example, in wireless networks in the context of facility location and backbone formation. In this paper we study the ability of a bioinspired, distributed algorithm, initially proposed for graph coloring, to generate large independent sets. The inspiration of the considered algorithm stems from the selfsynchronization capability of Japanese tree frogs. The experimental results confirm, indeed, that the algorithm has a strong tendency towards the generation of colorings in which the set of nodes assigned to the mostused color is rather large. Experimental results are compared to the ones of recent algorithms from the literature. Concerning solution quality, the results show that the froginspired algorithm has advantages especially for the application to rather sparse graphs. Concerning the computation round count, the algorithm has the advantage of converging within a reasonable number of iterations, regardless of the size and density of the considered graph.
20160405T12:13:40Z
Blum, Christian
Blesa Aguilera, Maria Josep
Calvo, Borja
The problem of identifying a maximal independent (node) set in a given graph is a fundamental problem in distributed computing. It has numerous applications, for example, in wireless networks in the context of facility location and backbone formation. In this paper we study the ability of a bioinspired, distributed algorithm, initially proposed for graph coloring, to generate large independent sets. The inspiration of the considered algorithm stems from the selfsynchronization capability of Japanese tree frogs. The experimental results confirm, indeed, that the algorithm has a strong tendency towards the generation of colorings in which the set of nodes assigned to the mostused color is rather large. Experimental results are compared to the ones of recent algorithms from the literature. Concerning solution quality, the results show that the froginspired algorithm has advantages especially for the application to rather sparse graphs. Concerning the computation round count, the algorithm has the advantage of converging within a reasonable number of iterations, regardless of the size and density of the considered graph.

Reactive clocks with variabilitytracking jitter
http://hdl.handle.net/2117/85192
Reactive clocks with variabilitytracking jitter
Cortadella Fortuny, Jordi; Lavagno, Luciano; López Muñoz, Pedro; Lupon Navazo, Marc; Moreno Vega, Alberto; Roca Pérez, Antoni; Sapatnekar, Sachin S.
The growing variability in nanoelectronic devices, due to uncertainties from the manufacturing process and environmental conditions (power supply, temperature, aging), requires increasing design guardbands, forcing circuits to work with conservative clock frequencies. Various schemes for clock generation based on ring oscillators and adaptive clocks have been proposed with the goal to mitigate the power and performance losses attributable to variability. However, there has been no systematic analysis to quantify the benefits of such schemes and no signoff method has been proposed for timing correctness. This paper presents and analyzes a Reactive Clocking scheme with VariabilityTracking Jitter (RClk) that uses variability as an opportunity to reduce power by continuously adjusting the clock frequency to the varying environmental conditions, and thus, reduces guardband margins significantly. Power can be reduced between 20% and 40% at isoperformance and performance can be boosted by similar amounts at isopower. Additionally, energy savings can be translated to substantial advantages in terms of reliability and thermal management. More importantly, the technology can be adopted with minimal modifications to conventional EDA flows.
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20160405T11:41:46Z
Cortadella Fortuny, Jordi
Lavagno, Luciano
López Muñoz, Pedro
Lupon Navazo, Marc
Moreno Vega, Alberto
Roca Pérez, Antoni
Sapatnekar, Sachin S.
The growing variability in nanoelectronic devices, due to uncertainties from the manufacturing process and environmental conditions (power supply, temperature, aging), requires increasing design guardbands, forcing circuits to work with conservative clock frequencies. Various schemes for clock generation based on ring oscillators and adaptive clocks have been proposed with the goal to mitigate the power and performance losses attributable to variability. However, there has been no systematic analysis to quantify the benefits of such schemes and no signoff method has been proposed for timing correctness. This paper presents and analyzes a Reactive Clocking scheme with VariabilityTracking Jitter (RClk) that uses variability as an opportunity to reduce power by continuously adjusting the clock frequency to the varying environmental conditions, and thus, reduces guardband margins significantly. Power can be reduced between 20% and 40% at isoperformance and performance can be boosted by similar amounts at isopower. Additionally, energy savings can be translated to substantial advantages in terms of reliability and thermal management. More importantly, the technology can be adopted with minimal modifications to conventional EDA flows.

Uncertainty in the cloud: an angeldaemon approach to modelling performance
http://hdl.handle.net/2117/84672
Uncertainty in the cloud: an angeldaemon approach to modelling performance
Stewart, Alan; Gabarró Vallès, Joaquim; Keenan, Anthony
Uncertainty profiles are used to study the effects of contention within cloud and servicebased environments. An uncertainty profile provides a qualitative description of an environment whose quality of service (QoS) may fluctuate unpredictably.
For example, the performance of an application running on a virtual machine can be affected both by the way in which resources are allocated at runtime as well as by hardware contention issues. The aim of this paper is to model the influence that cloud (or servicebased) environments can have on an application's performance.
%
Uncertain environments are modelled by strategic games with two agents; a daemon is used to represent overload and high resource contention; an angel is used to represent an idealised resource allocation situation with no underlying contention.
%An assessment of mixedstress situations is found by finding the Nash equilibria of games constructed from uncertainty profiles.
Assessments of uncertainty profiles are useful in two ways: firstly,
they provide a broad understanding of how environmental stress can effect an application's performance
(and reliability); secondly, they allow the effects of introducing redundancy into a computation to be assessed.
20160317T17:17:03Z
Stewart, Alan
Gabarró Vallès, Joaquim
Keenan, Anthony
Uncertainty profiles are used to study the effects of contention within cloud and servicebased environments. An uncertainty profile provides a qualitative description of an environment whose quality of service (QoS) may fluctuate unpredictably.
For example, the performance of an application running on a virtual machine can be affected both by the way in which resources are allocated at runtime as well as by hardware contention issues. The aim of this paper is to model the influence that cloud (or servicebased) environments can have on an application's performance.
%
Uncertain environments are modelled by strategic games with two agents; a daemon is used to represent overload and high resource contention; an angel is used to represent an idealised resource allocation situation with no underlying contention.
%An assessment of mixedstress situations is found by finding the Nash equilibria of games constructed from uncertainty profiles.
Assessments of uncertainty profiles are useful in two ways: firstly,
they provide a broad understanding of how environmental stress can effect an application's performance
(and reliability); secondly, they allow the effects of introducing redundancy into a computation to be assessed.