A compositional method for reliability analysis of workflows affected by multiple failure modes

We focus on reliability analysis for systems designed as workflow based compositions of components. Components are characterized by their failure profiles, which take into account possible multiple failure modes. A compositional calculus is provided to evaluate the failure profile of a composite system, given failure profiles of the components. The calculus is described as a syntax-driven procedure that synthesizes a workflows failure profile. The method is viewed as a design-time aid that can help software engineers reason about systems reliability in the early stage of development. A simple case study is presented to illustrate the proposed approach

Discrete-time dynamic modeling for software and services composition as an extension of the Markov chain approach

Discrete Time Markov Chains (DTMCs) and Continuous Time Markov Chains (CTMCs) are often used to model various types of phenomena, such as, for example, the behavior of software products. In that case, Markov chains are widely used to describe possible time-varying behavior of “self-adaptive” software systems, where the transition from one state to another represents alternative choices at the software code level, taken according to a certain probability distribution. From a control-theoretical standpoint, some of these probabilities can be interpreted as control signals and others can just be observed. However, the translation between a DTMC or CTMC model and a corresponding first principle model, that can be used to design a control system is not immediate. This paper investigates a possible solution for translating a CTMC model into a dynamic system, with focus on the control of computing systems components. Notice that DTMC models can be translated as well, providing additional information

A Metric Encoding for Bounded Model Checking (extended version)

In Bounded Model Checking both the system model and the checked property are translated into a Boolean formula to be analyzed by a SAT-solver. We introduce a new encoding technique which is particularly optimized for managing quantitative future and past metric temporal operators, typically found in properties of hard real time systems. The encoding is simple and intuitive in principle, but it is made more complex by the presence, typical of the Bounded Model Checking technique, of backward and forward loops used to represent an ultimately periodic infinite domain by a finite structure. We report and comment on the new encoding technique and on an extensive set of experiments carried out to assess its feasibility and effectiveness

L’influence de la variable niveau socioculturel dans les formes d’adresse

En el presente artículo se muestran los resultados obtenidos en un estudio sobre la incidencia de la variable nivel sociocultural en la elección de las formas de tratamiento tú y usted en el español peninsular actual. Para llevarlo a cabo, en primer lugar se han estudiado las principales características de esta compleja variable sociolingüística y, a continuación, se ha realizado una encuesta a una muestra de un total de 190 estudiantes con edades comprendidas entre los 18 y los 25 años residentes en la ciudad de Salamanca. Para ello, se ha creado una encuesta ad hoc que contiene distintas situaciones comunicativas en las que se combinan variables sociales y contextuales, de acuerdo con la bibliografía especializada. Los resultados se han procesado estadísticamente y permiten observar el importante papel que desempeña en la elección pronominal el nivel sociocultural del interlocutor y también –aunque en menor medida– el del propio hablante.This article shows the results obtained in a study about the incidence of the social class variables when choosing between the address forms tú and usted in current peninsular Spanish. In order to carry this study out, the main characteristics of this variable have been primarily studied, and secondly, a survey was given to a sample of 190 students with ages between 18 and 25 years old who reside in the city of Salamanca (Spain). To do that, an ad hoc survey has been created, containing different communicative situations that combine social and contextual variables, according to the specialized bibliography. The results have been statistically processed and allow us to observe the important role that social class variables of the interlocutor, but also –to a lesser extent– of the speaker, take when choosing one of the pronouns.Cet article présente les résultats obtenus au cours d’une étude sur l’incidence de la variable du niveau socioculturel dans l’élection des formes d’adresse tú et usted en espagnol péninsulaire actuel. Pour réaliser l’étude, nous avons présenté les caractéristiques principales de cette complexe variable sociolinguistique et, ensuite, nous avons effectué une enquête sur un total de 190 étudiants d’entre 18 et 25 ans qui résident à Salamanque (Espagne). Pour ce faire, nous avons créé une enquête ad hoc qui contient différentes situations communicatives dans lesquelles sont combinées variables sociales et contextuelles, conformément à la bibliographie spécialisée. Les résultats ont été traités statistiquement et permettent d’observer l’importance du rôle du niveau socioculturel de l’interlocuteur et du locuteur –à une moindre échelle– dans l’élection pronominale

Run-time efficient probabilistic model checking

Since the inception of discontinuous Galerkin (DG) methods for elliptic problems, there has existed a question of whether DG methods can be made more computationally efficient than continuous Galerkin (CG) methods. Fewer degrees of freedom, approximation properties for elliptic problems together with the number of optimization techniques, such as static condensation, available within CG framework made it challenging for DG methods to be competitive until recently. However, with the introduction of a static-condensation-amenable DG method—the hybridizable discontinuous Galerkin (HDG) method—it has become possible to perform a realistic comparison of CG and HDG methods when applied to elliptic problems. In this work, we extend upon an earlier 2D comparative study, providing numerical results and discussion of the CG and HDG method performance in three dimensions. The comparison categories covered include steady-state elliptic and time-dependent parabolic problems, various element types and serial and parallel performance. The postprocessing technique, which allows for superconvergence in the HDG case, is also discussed. Depending on the direct linear system solver used and the type of the problem (steady-state vs. time-dependent) in question the HDG method either outperforms or demonstrates a comparable performance when compared with the CG method. The HDG method however falls behind performance-wise when the iterative solver is used, which indicates the need for an effective preconditioning strategy for the method

MORPH: A Reference Architecture for Configuration and Behaviour Self-Adaptation

An architectural approach to self-adaptive systems involves runtime change of system configuration (i.e., the system's components, their bindings and operational parameters) and behaviour update (i.e., component orchestration). Thus, dynamic reconfiguration and discrete event control theory are at the heart of architectural adaptation. Although controlling configuration and behaviour at runtime has been discussed and applied to architectural adaptation, architectures for self-adaptive systems often compound these two aspects reducing the potential for adaptability. In this paper we propose a reference architecture that allows for coordinated yet transparent and independent adaptation of system configuration and behaviour

Supporting self-adaptation via quantitative verification and sensitivity analysis at run time

Modern software-intensive systems often interact with an environment whose behavior changes over time, often unpredictably. The occurrence of changes may jeopardize their ability to meet the desired requirements. It is therefore desirable to design software in a way that it can self-adapt to the occurrence of changes with limited, or even without, human intervention. Self-adaptation can be achieved by bringing software models and model checking to run time, to support perpetual automatic reasoning about changes. Once a change is detected, the system itself can predict if requirements violations may occur and enable appropriate counter-actions. However, existing mainstream model checking techniques and tools were not conceived for run-time usage; hence they hardly meet the constraints imposed by on-the-fly analysis in terms of execution time and memory usage. This paper addresses this issue and focuses on perpetual satisfaction of non-functional requirements, such as reliability or energy consumption. Its main contribution is the description of a mathematical framework for run-time efficient probabilistic model checking. Our approach statically generates a set of verification conditions that can be efficiently evaluated at run time as soon as changes occur. The proposed approach also supports sensitivity analysis, which enables reasoning about the effects of changes and can drive effective adaptation strategies

Abundances of Stars with Planets: Trends with Condensation Temperature

Precise abundances of 18 elements have been derived for ten stars known to host giant planets from high signal-to-noise ratio, high-resolution echelle spectroscopy. Internal uncertainties in the derived abundances are typically <=0.05 dex. The stars in our sample have all been previously shown to have abundances that correlate with the condensation temperature (T_c) of the elements in the sense of increasing abundances with increasing T_c; these trends have been interpreted as evidence that the stars may have accreted H-depleted planetary material. Our newly derived abundances also correlate positively with T_c, although slopes of linear least-square fits to the [m/H]-T_c relations for all but two stars are smaller here than in previous studies. When considering the refractory elements (T_c > 900 K) only, which may be more sensitive to planet formation processes, the sample can be separated into a group with positive slopes (four stars) and a group with flat or negative slopes (six stars). The four stars with positive slopes have very close-in giant planets (three at 0.05 AU) and slopes that fall above the general Galactic chemical evolution trend. We suggest that these stars have accreted refractory-rich planet material but not to the extent that would increase significantly the overall stellar metallicity. The flat or negative slopes of the remaining six stars are consistent with recent suggestions of a planet formation signature, although we show that the trends may be the result of Galactic chemical evolution.Comment: 64 pages (single column), 5 figures, 10 tables. Accepted by Ap