Ugo A. Buy

Clock synchronization for wireless sensor networks: a survey

Abstract Recent advances in micro-electromechanical (MEMS) technology have led to the development of small, low-cost, and low-power sensors. Wireless sensor networks (WSNs) are large-scale networks of such sensors, dedicated to observing and monitoring various aspects of the physical world. In such networks, data from each sensor is agglomerated using data fusion to form a single meaningful result, which makes time synchronization between sensors highly desirable. This paper surveys and evaluates existing clock synchronization protocols based on a palette of factors like precision, accuracy, cost, and complexity. The design considerations presented here can help developers either in choosing an existing synchronization protocol or in defining a new protocol that is best suited to the specific needs of a sensor-network application. Finally, the survey provides a valuable framework by which designers can compare new and existing synchronization protocols.

Automated analysis of concurrent systems with the constrained expression toolset

The constrained expression approach to analysis of concurrent software systems can be used with a variety of design and programming languages and does not require a complete enumeration of the set of reachable states of the concurrent system. The construction of a toolset automating the main constrained expression analysis techniques and the results of experiments with that toolset are reported. The toolset is capable of carrying out completely automated analyses of a variety of concurrent systems, starting from source code in an Ada-like design language and producing system traces displaying the properties represented bv the analysts queries. The strengths and weaknesses of the toolset and the approach are assessed on both theoretical and empirical grounds. >

Automated Testing of Classes

Programs developed with object technologies have unique features that often make traditional testing methods inadequate. Consider, for instance, the dependence between the state of an object and the behavior of that object: The outcome of a method executed by an object often depends on the state of the object when the method is invoked. It is therefore crucial that techniques for testing of classes exercise class methods when the methods receiver is in different states. The state of an object at any given time depends on the sequence of messages received by the object up to that time. Thus, methods for testing object-oriented software should identify sequences of method invocations that are likely to uncover potential defects in the code under test. However, testing methods for traditional software do not provide this kind of information. In this paper, we use data flow analysis, symbolic execution, and automated deduction to produce sequences of method invocations exercising a class under test. Since the static analysis techniques that we use are applied to different subproblems, the method proposed in this paper can automatically generate information relevant to testing even when symbolic execution and automated deduction cannot be completed successfully.

Reduction rules for time Petri nets

The goal of net reduction is to increase the effectiveness of Petri-netbased real-time program analysis. Petri-net-based analysis, like all reachabilitybased methods, suffers from the state explosion problem. Petri net reduction is one key method for combating this problem.In this paper, we extend several rules for the reduction of ordinary Petri nets to work with time Petri nets. We introduce a notion of equivalence among time Petri nets, and prove that our reduction rules yield equivalent nets. This notion of equivalence guarantees that crucial timing and concurrency properties are preserved.

Application and experimental evaluation of state space reduction methods for deadlock analysis in Ada

An emerging challenge for software engineering is the development of the methods and tools to aid design and analysis of concurrent and distributed software. Over the past few years, a number of analysis methods that focus on Ada tasking have been developed. Many of these methods are based on some form of reachability analysis, which has the advantage of being conceptually simple, but the disadvantage of being computationally expensive. We explore the effectiveness of various Petri net-based techniques for the automated deadlock analysis of Ada programs. Our experiments consider a variety of state space reduction methods both individually and in various combinations. The experiments are applied to a number of classical concurrent programs as well as a set of “real-world” programs. The results indicate that Petri net reduction and reduced state space generation are mutually beneficial techniques, and that combined approaches based on Petri net models are quite effective, compared to alternative analysis approaches.

Language independent gender classification on Twitter

Online Social Networks (OSNs) generate a huge volume of user-originated texts. Gender classification can serve multiple purposes. For example, commercial organizations can use gender classification for advertising. Law enforcement may use gender classification as part of legal investigations. Others may use gender information for social reasons. Here we explore language independent gender classification. Our approach predicts gender using five color-based features extracted from Twitter profiles (e.g., the background color in a users profile page). Most other methods for gender prediction are typically language dependent. Those methods use high-dimensional spaces consisting of unique words extracted from such text fields as postings, user names, and profile descriptions. Our approach is independent of the users language, efficient, and scalable, while attaining a good level of accuracy. We prove the validity of our approach by examining different classifiers over a large dataset of Twitter profiles.

Control Reconfiguration of Discrete Event Systems With Dynamic Control Specifications

This paper defines a reconfiguration method for the class of discrete-event systems (DES) that is subject to linear constraints as their control specifications. Some existing methods for enforcing these constraints make use of Petri-net P-invariants for controller synthesis. These methods are quite appealing because their computational complexity is much more tractable than most other methods for controller synthesis. However, a common limitation of all existing P-invariant-based control architectures for DES plants is the assumption that the linear constraints defining the control specification of the plant do not change over time. Here, we relax this assumption and allow the control specifications to change during controller runtime. Under certain assumptions on DES behavior, we automatically reconfigure the DES controller after the control specification is changed. In addition, if the current state of the controlled DES has become infeasible under the new control specification, we automatically generate a so-called plant reconfiguration procedure whose execution leads the system back to a feasible state. This reconfiguration procedure is optimal in that it seeks to minimize the cost of reconfiguration actions through an Integer Programming (IP) model. The objective function of the IP model can be used to generate reconfiguration solutions that meet some desired properties. Depending on the cost of each reconfiguration action, a minimum cost reconfiguration solution may use only actions contained in the current plant configuration (an internal response), or ask for a change in the plant configuration, for instance, by adding new resources (an external response), or a combination of both strategies. Finally, we illustrate our method by applying it to a hospital control system example. Note to Practitioners-This paper proposes a dynamic reconfiguration framework that can revise the operations of systems whose control requirements change over time. The proposed framework can be applied to systems that satisfy the following two assumptions. First, the behavior of the system under study is described in terms of a set of discrete states and events. Events will cause the system to transition between states. Second, the control requirements must be expressed by linear equalities and inequalities on the system states. Under these circumstances, the proposed framework can identify an optimal transition to a new control policy that satisfies the new control requirements. Moreover, the system under consideration will continue operating while this transition is taking place. One application of this method is in modifying hospital control strategies when a hospital experiences unexpected events. In this case, the hospital operations-such as patient handling, resource assignment, and procedure scheduling-can be represented by discrete state models (e.g., Petri nets). Constraints on these operations can be modeled by linear inequalities on hospital and patient state. Upon a change in the constraints, the proposed reconfiguration method revises the hospital control strategies. For example, a shift in the hospital service demands (e.g., an increase in the flow of patients to the hospital due to a mass casualty situation) can be translated to changes in the constraints. In this case, the hospital operations must be revised to accommodate the new constraints without disrupting the operation of the hospital. The reconfiguration method of this paper provides a framework for modeling the reconfiguration steps and for calculating the least cost reconfiguration solution.

Using state space reduction methods for deadlock analysis in Ada tasking

Over the past few years, a number of research investigations have been initiated for static analysis of concurrent and distributed software. In this paper we report on experiments with various optimization techniques for reachability-based deadlock detection in Ada programs using Petri net models. Our experimental results show that various optimization techniques are mutually beneficial with respect to the effectiveness of the analysis.

Analysis of real-time programs with simple time Petri nets

We present a first report on our PARTS toolset for the automated static analysis of real-time systems. The PARTS toolset is based upon a timed extension of Petri nets. Our simple time Petri nets or STP nets are specifically aimed at facilitating real-time analysis. Our analysis approach uses the state space of an STP net in order to answer queries about the concurrency and timing behavior of the corresponding system. An attractive feature of STP nets is that they support a variety of techniques for controlling the number of states that must be explicitly enumerated. These techniques were originally defined for the analysis of concurrency properties of untimed systems, and in this paper we discuss the extension of each to the timed domain. We also report on some preliminary experimental results that we obtained by running our toolset on examples of real-time systems.

Empirical Evaluation of Profile Characteristics for Gender Classification on Twitter

Online Social Networks (OSNs) provide reliable communication among users from different countries. The volume of texts generated by OSNs is huge and highly informative. Gender classification can serve commercial organizations for advertising, law enforcement for legal investigation, and others for social reasons. Here we explore profile characteristics for gender classification on Twitter. Unlike existing approaches to gender classification that depend heavily on posted text such as tweets, here we study the relative strengths of different characteristics extracted from Twitter profiles (e.g., first name and background color in a users profile page). Our goal is to evaluate profile characteristics with respect to their predictive accuracy and computational complexity. In addition, we provide a novel technique to reduce the number of features of text-based profile characteristics from the order of millions to a few thousands and, in some cases, to only 40 features. We prove the validity of our approach by examining different classifiers over a large dataset of Twitter profiles.