Efficient Algorithms for Discovering Concept Drift in Business Processes.

Protsessikaeve on suhteliselt uus, kuid ühiskonna poolt juba kasutusele võetud uurimisvaldkond. Paljud ettevõtted ja asutused rakendavad erinevaid infosüsteemidega toetatud protsesse, mille käivitamisest jäävad maha sündmuste logid. Neid logisid analüüsides saab ehitada mudeli, mis kajastab, kuidas need protsessid reaalselt toimivad. Tänapäevased algoritmid eeldavad, et analüüsitav protsess on stabiilne, kuid tegelikult võib seda mõjutada hooaegsus, uus seadus või mõni väline sündmus – näiteks järsk majanduslangus. Sellisel juhul on tegemist kontseptsiooninihkega. Kontseptsiooninihked võivad olla järsud (kui protsessi muutus on äkiline) või järkjärgulised (kui üks protsessivariant asendub teisega sujuvalt). Antud töös pakkusime välja viis uudset lähenemist kontseptsiooninihke avastamiseks protsessikaeves. Igaüks neist parandab või laiendab algset Bose poolt kirjeldatud algoritmi [1]. Sammu pikkuse suurendamine võimaldab algoritmi kiirendada, jättes välja mõned vahepealsed sammud. Muutmispunkti automaatne leidmine võimaldab ekstraheerida kontseptsiooninihke punktid ilma manuaalse analüüsita. Adapteerivate akende algoritm (ADWIN) pehmendab originaalse algoritmi sõltuvust populatsiooni suurusest, seega vähendab vale-positiivsete ja vale-negatiivsete tulemuste arvu. Mittejärjestikkuste populatsioonidega algoritm võimaldab uurida järkjärgulisi kontseptsiooninihkeid. Lisaks lubab populatsioonide suuruste määramine ajaliste perioodide kaupa (jälgede koguse asemel) leida mikro-taseme ja makro-taseme nihked multi-taseme dünaamikaga logides, kus protsess muutub mitmel detailsuse tasemel. Kõik algoritmid olid implementeetirud ProM raamistiku Concept Drift moodulis. Algoritmide kvaliteedi hindamiseks pakub käesolev töö välja meetodi, kus CPN Tools programmi abil genereeritakse logisid erinevate kontseptsiooninihke tunnustega. Samuti on välja arendatud kvaliteedi hindamise raamistik, mis sarnaneb sellega, mis on kasutusel infootsingu valdkonnas ning mis hõlmab endas tegelike positiivsete, valepositiivsete ja valenegatiivsete väärtuste loendamist ning tuletatud meetrikate arvutamist. Algoritmid olid edukalt testitud nii simuleeritud, kui ka päriselu andmetega. [1] Bose, R.P.J.C., van der Aalst, W.M.P., Žliobaitė, I., Pechenizkiy, M.: Handling Concept Drift in Process Mining. In: CAiSE. LNCS, vol. 6741, pp. 391–405.Springer, Berlin (2011)Process mining is a relatively new research area, but it is already used in practice. Every company and organization run different business processes, which are supported by information systems and which leave event logs while being executed. By analyzing those logs one can build a process model, which reflects how the process operates in reality.Existing algorithms assume that the analyzed process is in steady state, however it could be altered because of seasonality, a new law or some event, like a financial crisis. In this case, we have to deal with concept drift. Concept drifts can be sudden, when the change is abrupt and gradual, where one concept fades gradually while the other takes over. In this work we proposed five novel approaches for detecting concept drifts in process mining. All of them improve or expand the algorithm, proposed by Bose et al [1]. Step size improvement allows to speed up the algorithm by leaving out some intermediate steps. Automatic change point detection algorithm allows to extract the concept drift points without the need to analyze the plot manually. The adaptive windows algorithm (ADWIN) relaxes the original algorithm's dependency on the fixed population size, thus reducing the amount of false positives and false negatives. The algorithm with non-continuous populations allows to deal with gradual drifts. And finally, defining the population sizes in terms of time periods instead of trace amount allows to detect micro-level and macro-level drifts in logs with multi-order dynamics, where process changes can happen on multiple level of granularity. The algorithms were implemented in the Concept Drift plug-in of ProM framework. For assessing the quality of algorithms, we proposed a way to generate logs with different concept drift characteristics using CPN Tools and a quality evaluation framework, similar to the one used in the field information retrieval, involving calculating true positives, false positives, false negative and derived metrics. The algotihms were successfully tested on both simulated and real-life data. [1] Bose, R.P.J.C., van der Aalst, W.M.P., Žliobaitė, I., Pechenizkiy, M.: Handling Concept Drift in Process Mining. In: CAiSE. LNCS, vol. 6741, pp. 391–405.Springer, Berlin (2011

Representing Dependencies in Event Structures

Event structures where the causality may explicitly change during a computation have recently gained the stage. In this kind of event structures the changes in the set of the causes of an event are triggered by modifiers that may add or remove dependencies, thus making the happening of an event contextual. Still the focus is always on the dependencies of the event. In this paper we promote the idea that the context determined by the modifiers plays a major role, and the context itself determines not only the causes but also what causality should be. Modifiers are then used to understand when an event (or a set of events) can be added to a configuration, together with a set of events modeling dependencies, which will play a less important role. We show that most of the notions of Event Structure presented in literature can be translated into this new kind of event structure, preserving the main notion, namely the one of configuration

A Goal-Oriented Approach for Adaptive SLA Monitoring : a Cloud Provider Case Study

National audienceWe argue in this paper that autonomic systems need to make their integrated monitoring adaptive in order to improve their “comprehensive” Quality of Service (QoS). We propose to design this adaptation based on high level objectives (called goals) related to the management of both the “functional system QoS” and the “monitoring system QoS”. Starting from some previous works suggesting a model-driven adaptable monitoring framework composed of 3 layers (configurability, adaptability, governability), we introduce a methodology to identify the functional and monitoring high level goals (according to the agreed Service Level Agreement - SLA) in order to drive models' instantiation. This proposal is first applied to a cloud provider case study for which two high level goals are developed (respect metrics freshness and minimize monitoring cost), and then simulated to show how the quality of management decisions, as well as intelligent monitoring of dynamic SLA, could be improved

Contributions to the deadlock problem in multithreaded software applications observed as Resource Allocation Systems

Desde el punto de vista de la competencia por recursos compartidos sucesivamente reutilizables, se dice que un sistema concurrente compuesto por procesos secuenciales está en situación de bloqueo si existe en él un conjunto de procesos que están indefinidamente esperando la liberación de ciertos recursos retenidos por miembros del mismo conjunto de procesos. En sistemas razonablemente complejos o distribuidos, establecer una política de asignación de recursos que sea libre de bloqueos puede ser un problema muy difícil de resolver de forma eficiente. En este sentido, los modelos formales, y particularmente las redes de Petri, se han ido afianzando como herramientas fructíferas que permiten abstraer el problema de asignación de recursos en este tipo de sistemas, con el fin de abordarlo analíticamente y proveer métodos eficientes para la correcta construcción o corrección de estos sistemas. En particular, la teoría estructural de redes de Petri se postula como un potente aliado para lidiar con el problema de la explosión de estados inherente a aquéllos. En este fértil contexto han florecido una serie de trabajos que defienden una propuesta metodológica de diseño orientada al estudio estructural y la correspondiente corrección física del problema de asignación de recursos en familias de sistemas muy significativas en determinados contextos de aplicación, como el de los Sistemas de Fabricación Flexible. Las clases de modelos de redes de Petri resultantes asumen ciertas restricciones, con significado físico en el contexto de aplicación para el que están destinadas, que alivian en buena medida la complejidad del problema. En la presente tesis, se intenta acercar ese tipo de aproximación metodológica al diseño de aplicaciones software multihilo libres de bloqueos. A tal efecto, se pone de manifiesto cómo aquellas restricciones procedentes del mundo de los Sistemas de Fabricación Flexible se muestran demasiado severas para aprehender la versatilidad inherente a los sistemas software en lo que respecta a la interacción de los procesos con los recursos compartidos. En particular, se han de resaltar dos necesidades de modelado fundamentales que obstaculizan la mera adopción de antiguas aproximaciones surgidas bajo el prisma de otros dominios: (1) la necesidad de soportar el anidamiento de bucles no desplegables en el interior de los procesos, y (2) la posible compartición de recursos no disponibles en el arranque del sistema pero que son creados o declarados por un proceso en ejecución. A resultas, se identifica una serie de requerimientos básicos para la definición de un tipo de modelos orientado al estudio de sistemas software multihilo y se presenta una clase de redes de Petri, llamada PC2R, que cumple dicha lista de requerimientos, manteniéndose a su vez respetuosa con la filosofía de diseño de anteriores subclases enfocadas a otros contextos de aplicación. Junto con la revisión e integración de anteriores resultados en el nuevo marco conceptual, se aborda el estudio de propiedades inherentes a los sistemas resultantes y su relación profunda con otros tipos de modelos, la confección de resultados y algoritmos eficientes para el análisis estructural de vivacidad en la nueva clase, así como la revisión y propuesta de métodos de resolución de los problemas de bloqueo adaptadas a las particularidades físicas del dominio de aplicación. Asimismo, se estudia la complejidad computacional de ciertas vertientes relacionadas con el problema de asignación de recursos en el nuevo contexto, así como la traslación de los resultados anteriormente mencionados sobre el dominio de la ingeniería de software multihilo, donde la nueva clase de redes permite afrontar problemas inabordables considerando el marco teórico y las herramientas suministradas para subclases anteriormente explotadas

Dynamic Causality in Event Structures

Event Structures (ESs) address the representation of direct relationships between individual events, usually capturing the notions of causality and conflict. Up to now, such relationships have been static, i.e., they cannot change during a system run. Thus, the common ESs only model a static view on systems. We make causality dynamic by allowing causal dependencies between some events to be changed by occurrences of other events. We first model and study the case in which events may entail the removal of causal dependencies, then we consider the addition of causal dependencies, and finally we combine both approaches in the so-called Dynamic Causality ESs. For all three newly defined types of ESs, we study their expressive power in comparison to the well-known Prime ESs, Dual ESs, Extended Bundle ESs, and ESs for Resolvable Conflicts. Interestingly, Dynamic Causality ESs subsume Extended Bundle ESs and Dual ESs but are incomparable with ESs for Resolvable Conflicts

Automatic 3D model creation with velocity-based surface deformations

The virtual worlds of Computer Graphics are populated by geometric objects, called models. Researchers have addressed the problem of synthesizing models automatically. Traditional modeling approaches often require a user to guide the synthesis process and to look after the geometry being synthesized, but user attention is expensive, and reducing user interaction is therefore desirable. I present a scheme for the automatic creation of geometry by deforming surfaces. My scheme includes a novel surface representation; it is an explicit representation consisting of points and edges, but it is not a traditional polygonal mesh. The novel surface representation is paired with a resampling policy to control the surface density and its evolution during deformation. The surface deforms with velocities assigned to its points through a set of deformation operators. Deformation operators avoid the manual computation and assignment of velocities, the operators allow a user to interactively assign velocities with minimal effort. Additionally, Petri nets are used to automatically deform a surface by mimicking a user assigning deformation operators. Furthermore, I present an algorithm to translate from the novel surface representations to a polygonal mesh. I demonstrate the utility of my model generation scheme with a gallery of models created automatically. The scheme's surface representation and resampling policy enables a surface to deform without requiring a user to control the deformation; self-intersections and hole creation are automatically prevented. The generated models show that my scheme is well suited to create organic-like models, whose surfaces have smooth transitions between surface features, but can also produce other kinds of models. My scheme allows a user to automatically generate varied instances of richly detailed models with minimal user interaction