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PrePrint: Atomicity Analysis of Service Composition across Organizations
Atomicity is a highly desirable property for achieving application consistency in service compositions. To achieve atomicity, a service composition should satisfy the atomicity sphere, a structural criterion for the backend processes of involved services. Existing analysis techniques for atomicity sphere generally assume complete knowledge of all involved backend processes. Such an assumption is invalid when some service providers do not release all details of their backend processes to service consumers outside the organizations. To address this problem, we propose a process algebraic framework to publish atomicity-equivalent public views from the backend processes. These public views extract relevant task properties and reveal only partial process details that service providers need to expose. Our framework enables the analysis of atomicity sphere for service compositions using these public views instead of their backend processes. This allows service consumers to choose suitable services such that their composition satisfies the atomicity sphere without disclosing the details of their backend processes. Based on the theoretical result, we present algorithms to construct atomicity-equivalent public views and to analyze the atomicity sphere for a service composition. Two case studies from supply chain and insurance domains are given to evaluate our proposal and demonstrate the applicability of our approach.
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PrePrint: Optimized Resource Allocation for Software Release Planning
Release planning for incremental software development assigns features to releases such that technical, resource, risk and budget constraints are met. Planning of software releases and allocation of resources cannot be handled in isolation. A feature can be offered as part of a release only if all its necessary tasks are done before the given release date. We assume a given pool of human resources with different degrees of productivity to perform different types of tasks. To address the inherent difficulty of this process, we propose a two-phased optimization approach that combines the strength of two existing solution methods. The industrial applicability of the approach is primarily directed towards mature organizations having systematic development and measurement processes in place. The expected practical benefit of the planning method is to provide release plan solutions that achieve a better overall business value (e.g., expressed by the degree of stakeholder satisfaction) by better allocation of resources. Without ignoring the importance of the human expert in this process, the contributions of the paper are seen in making the overall process more objective and the resulting decisions more transparent.
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PrePrint: CoMoM: Efficient Class-Oriented Evaluation of Multiclass Performance Models
We introduce the Class-oriented Method of Moments (CoMoM), a new exact algorithm to efficiently compute normalizing constants and marginal queue-length probabilities in closed multiclass queueing networks. Closed models are important for performance evaluation of multi-tier applications, but when the number of service classes is large they become too expensive to solve with existing methods, such as Mean Value Analysis (MVA). CoMoM addresses this limitation by a new recursion that scales efficiently with the number of classes. Compared to the MVA algorithm, which recursively computes mean queue-lengths, CoMoM carries on in the recursion also information on higher-order moments of queue-lengths. We show that this additional information minimizes the number of recursive steps needed to solve the model and makes CoMoM the best-available algorithm for networks with several classes. For example, we show a model of a real J2EE application where CoMoM is several orders of magnitude faster and more memory-efficient than MVA. We conclude the paper by generalizing CoMoM to the efficient computation of marginal queue-length probabilities, which finds application in the evaluation of state-dependent indexes such as energy consumption or quality-of-service metrics.
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PrePrint: Model Checking Probabilistic and Stochastic Extensions of the ?-calculus
We present an implementation of model checking for probabilistic and stochastic extensions of the ?-calculus, a process algebra which supports modelling of concurrency and mobility. Formal verification techniques for such extensions have clear applications in several domains, including mobile ad-hoc network protocols, probabilistic security protocols and biological pathways. Despite this, no implementation of automated verification exists. Building upon the ?-calculus model checker MMC, we first show an automated procedure for constructing the underlying semantic model of a probabilistic or stochastic ?-calculus process. This can then be verified using existing probabilistic model checkers such as PRISM. Secondly, we demonstrate how for processes of a specific structure a more efficient, compositional approach is applicable, which uses our extension of MMC on each parallel component of the system and then translates the results into a high-level modular description for the PRISM tool. The feasibility of our techniques is demonstrated through a number of case studies from the ?-calculus literature.
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PrePrint: Predicting Project Velocity in XP using a Learning Dynamic Bayesian Network Model
Bayesian networks, which can combine sparse data, prior assumptions and expert judgment into a single causal model, have already been used to build software effort prediction models. We present such a model of an Extreme Programming environment and show how it can learn from project data in order to make quantitative effort predictions and risk assessments without requiring any additional metrics collection program. The model's predictions are validated against a real world industrial project, with which they are in good agreement.
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PrePrint: Automated Trace Analysis of Discrete Event System Models
In this paper, we describe a novel technique that helps a modeler gain insight into the dynamic behavior of a complex stochastic discrete event simulation model based on trace analysis. We propose algorithms to distinguish progressive from repetitive behavior in a trace and to extract a minimal progressive fragment of a trace. The implied combinatorial optimization problem for trace reduction is solved in linear time with dynamic programming. We present and compare several approximate and one exact solution method. Information on the reduction operation as well as the reduced trace itself helps a modeler to recognize the presence of certain errors and to identify their cause. We track down a subtle modeling error in a dependability model of a multi-class server system to illustrate the effectiveness of our approach in revealing the cause of an observed effect. The proposed technique has been implemented and integrated in Traviando, a trace analyzer to debug stochastic simulation models.
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PrePrint: Enhanced Modeling and Solution of Layered Queueing Networks
Layered queues are a canonical form of extended queueing network for systems with nested multiple resource possession, in which successive depths of nesting define the layers. The model has been applied to most modern distributed systems, which use different kinds of client-server and master-slave relationships, and scales up well. The Layered Queueing Network (LQN) model is described here in a unified fashion, including its many more extensions to match the semantics of sophisticated practical distributed and parallel systems. These include efficient representation of replicated services, parallel and quorum execution, and dependability analysis under failure and reconfiguration. The full LQN model is defined here and its solver is described. A substantial case study to an air traffic control system shows errors (compared to simulation) of a few percent. The LQN model is compared to other models and solutions, and is shown to cover all their features.
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PrePrint: Mutation Operators for Spreadsheets
Based on (1) research into mutation testing for general purpose programming languages, and (2) spreadsheet errors that have been reported in the literature, we have developed a suite of mutation operators for spreadsheets. We present an evaluation of the mutation adequacy of du-adequate test suites generated by a constraint-based automatic test-case generation system we have developed in previous work. The results of the evaluation suggest additional constraints that can be incorporated into the system to target mutation adequacy. In addition to being useful in mutation testing of spreadsheets, the operators can be used in the evaluation of error-detection tools and also for seeding spreadsheets with errors for empirical studies. We describe two case studies where the suite of mutation operators helped us carry out such empirical evaluations. The main contribution of this paper is a suite of mutation operators for spreadsheets that can be used for carrying out empirical evaluations of spreadsheet tools to indicate ways in which the tools can be improved.
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PrePrint: What Types of Defects Are Really Discovered in Code Reviews?
Research on code reviews has often focused on defect counts instead of defect types, which offers an imperfect view of code review benefits. In this paper, we classified the defects of 9 industrial (C/C++) and 23 student (Java) code reviews, detecting 388 and 371 defects, respectively. First, we discovered that 75% of defects found during the review do not affect the visible functionality of the software. Instead, these defects improved software evolvability by making it easier to understand and modify. Second, we created a defect classification consisting of functional and evolvability defects. The evolvability defect classification is based on the defect types found in this study, but for the functional defects, we studied and compared existing functional defect classifications. The classification can be useful for assigning code review roles, creating checklists, assessing software evolvability, and building software engineering tools. We conclude that, in addition to functional defects, code reviews find many evolvability defects and, thus, offer additional benefits over execution based quality assurance methods that cannot detect evolvability defects. We suggest that code reviews may be most valuable for software products with long life-cycles, as the value of discovering evolvability defects in them is greater than for short life-cycle systems.
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PrePrint: The Effectiveness of Software Diversity in a Large Population of Programs
In this paper, we first present an exploratory analysis of the aspects of multiple-version software diversity using 36,123, programs written to the same specification. We do so within the framework of the theories of Eckhardt & Lee and Littlewood & Miller. We analyse programming faults made, explore failure regions and difficulty functions, show how effective 1-out-of-2 diversity is and how language diversity increases this effectiveness. The second part of the paper generalizes the findings about 1-out-of-2 diveristity, and its special case language diversity by performing statistical analyses of 89,402 programs written to 60 specifications. Most observations in the exploratory analysis are confirmed; however, although the benefit of language diversity can be observed, its effectiveness appears to be low.
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PrePrint: An Empirical Study on the Relationship Between Software Design Quality, Development Effort and Governance in Open Source Projects
The relationship among software design quality, development effort, and governance practices is a traditional research problem. However, the extent to which consolidated results on this relationship remain valid for open source (OS) projects is an open research problem. An emerging body of literature contrasts the view of open source as an alternative to proprietary software and explains that there exists a continuum between closed and open source projects. This paper hypothesizes that as projects approach the OS end of the continuum, governance becomes less formal. In turn a less formal governance is hypothesized to require a higher-quality code as a means to facilitate coordination among developers by making the structure of code explicit and facilitate quality by removing the pressure of deadlines from contributors. However, a less formal governance is also hypothesized to increase development effort due to a more cumbersome coordination overhead. The verification of research hypotheses is based on empirical data from a sample of 75 major OS projects. Empirical evidence supports our hypotheses and suggests that software quality, mainly measured as coupling and inheritance, does not increase development effort, but represents an important managerial variable to implement the more open governance approach that characterizes OS projects which, in turn, increases development effort.
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PrePrint: Extracting Interactions in Component Based Systems
Monitoring, analysing and understanding component based enterprise software systems are challenging tasks. These tasks are essential in solving and preventing performance and quality problems. Obtaining component level interactions which show the relationships between different software entities is a necessary prerequisite for such efforts. This paper focuses on component based Java applications, currently widely used by industry. They pose specific challenges while raising interesting opportunities for component level interaction extraction tools. We present a range of representative approaches for dynamically obtaining and using component interactions. For each approach we detail the needs it addresses, and the technical requirements for building an implementation of the approach. We also take a critical look at the different available implementations of the various techniques presented. We give performance and functional considerations and contrast them against each other by outlining their relative advantages and disadvantages. Based on this data, developers and system integrators can better understand the current state-of-the-art and the implications of choosing or implementing different dynamic interaction extraction techniques.
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PrePrint: A Systematic Study of Failure Proximity
Software end-users are the best testers, who keep revealing bugs in software that has undergone rigorous in-house testing. In order to leverage their testing efforts, failure reporting components have been widely deployed in released software. Many utilities of the collected failure data depend on an effective failure indexing technique, which, at the optimal case, would index all failures due to the same bug together. Unfortunately, the problem of failure proximity, which underpins the effectiveness of an indexing technique, has not been systematically studied. This article presents the first systematic study of failure proximity. A failure proximity consists of two components: a fingerprinting function that extracts signatures from failures, and a distance function that calculates the likelihood of two failures being due to the same bug. By considering different instantiations of the two functions, we study an array of six failure proximities (two of them are new) in this article. These proximities range from the simplest approach that checks failure points to the most sophisticated approach that utilizes fault localization algorithms to extract failure signatures. Besides presenting technical details of each proximity, we also study the properties of each proximity and tradeoffs between proximities. These altogether deliver a systematic view of failure proximity.
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PrePrint: Bayesian Network Models for Web Effort Prediction: A Comparative Study
OBJECTIVE The objective of this paper is to compare, using a cross-company dataset, several Bayesian Network (BN) models for Web effort estimation. METHOD Eight BNs were built; four automatically using Hugin and PowerSoft tools with two training sets, each with 130 Web projects from the Tukutuku database; four using a causal graph elicited by a domain expert, with parameters automatically fit using the same training sets used in the automated elicitation (hybrid models). Their accuracy was measured using two validation sets, each containing data on 65 projects, and point estimates. As a benchmark, the BN-based estimates were also compared to estimates obtained using Manual StepWise Regression (MSWR), Case-Based Reasoning (CBR), mean- and median-based effort models. RESULTS MSWR presented significantly better predictions than any of the BN models built herein, and in addition was the only technique to provide significantly superior predictions to a Median-based effort model. CONCLUSIONS This paper investigated data-driven and hybrid BN models using project data from the Tukutuku database. Our results suggest that the use of simpler models, such as the median effort, can outperform more complex models, such as BNs. In addition, MSWR seemed to be the only effective technique for Web effort estimation.
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PrePrint: Timed Automata Patterns
Timed Automata have proven to be useful for specification and verification of real-time systems. System design using Timed Automata relies on explicit manipulation of clock variables. A number of automated analyzers for Timed Automata have been developed. However, Timed Automata lack of composable patterns for high-level system design. Logic-based specification languages like Timed CSP and TCOZ are well suited for presenting compositional models of complex real-time systems. In this work, we define a set of composable Timed Automata patterns based on hierarchical constructs in timed enriched process algebras. The patterns facilitate hierarchical design of complex systems using Timed Automata. They also allow a systematic translation from Timed CSP/TCOZ models to Timed Automata so that analyzers for Timed Automata can be used to reason about TCOZ models. A prototype has been developed to support system design using Timed Automata patterns or, if given a TCOZ specification, to automate the translation from TCOZ to Timed Automata.
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PrePrint: Compositional Control of IP Media
In many IP media services, the media channels are point-to-point, dynamic, and set up with the participation of one or more application servers, even thou the media packets themselves travel directly between media endpoints. The application servers must be programmed so that media behavior is globally correct, even though the servers may attempt to manipulate the same media channels concurrently and without knowledge of each other. Our proposed solution to this problem of compositional media control includes an architecture-independent descriptive model, a set of high-level programming primitives, a formal specification of their compositional semantics, a signaling protocol, an implementation, and partial verification of correctness. The paper includes performance analysis, comparison to related work, and principles for making other networked applications more compositional.
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PrePrint: The Impact of Educational Background on the Effectiveness of Requirements Inspections: An Empirical Study
While the inspection of various software artifacts increases the quality of the end product, the effectiveness of an inspection depends largely on the individual inspectors involved. To address that issue, a large-scale controlled inspection experiment with over 70 professionals was conducted at Microsoft Corporation that focused on the relationship between an inspector's background and their effectiveness during a requirements inspection. The results of the study showed that inspectors with university degrees in majors not related to computer science found significantly more defects than those with degrees in computer science majors. We also observed that level of education (Masters, PhD), prior industrial experience or other job related experiences did not significantly impact the effectiveness of an inspector. The only other type of experience that had a significant impact on effectiveness was experience in writing requirements, i.e. professionals with prior experience writing requirements found statistically significant more defects than their counterparts.
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PrePrint: A Study of Uncertainty in Software Cost and Its Impact on Optimal Software Release Time
For a development software project, management often faces the dilemma of when to stop testing the software and release it for operation, which requires careful decision-making as it has great impact on both software reliability and project cost. In most existing research on optimal software release problem, the cost considered was the expected cost (EC) of the project. However, what management concerns is the actual cost (AC) of the project rather than the EC. Treatment (such as minimization) of the EC may not ensure a desired low level of the AC, due to the uncertainty (variability) involved in the AC. In this paper, we study the uncertainty in software cost and its impact on optimal software release time in detail. The uncertainty is quantified by the variance of the AC and several risk functions. A risk-control approach to optimal software release problem is proposed. New formulations of the problem which are extensions of current formulations are developed, and solution procedures are established. Several examples are presented. Results reveal that it seems crucial to take account of the uncertainty in software cost in optimal software release problem, otherwise unsafe decision may be reached which could be a false dawn to management.
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PrePrint: Dynamic QoS Adaptation for Mobile Middleware
Computation and networking resources in mobile operating environments are much scarcer and more dynamic than in desktop operating environments. Mobile applications can leverage on the benefits of adaptive computing to optimize the QoS delivery based on contextual situations. Fuzzy control models have been successfully applied to various distributed network QoS management systems. However, existing models are either application-specific or limited to abstract modeling and simple conceptual scenarios which do not take into account overall model scalability. Specifically, the large number of QoS parameters in a mobile operating environment causes an exponential increase in the number of rules correspondingly increases the demand for processing power to infer the rules. Hierarchical fuzzy systems were introduced to reduce the number of rules using hierarchical fuzzy control, in which correlated linguistic variables are hierarchically inferred and grouped into abstract linguistic variables. In this paper, we propose a mobile QoS management framework that uses a hierarchical fuzzy control model to support a highly extensible and structured adaptation paradigm. The proposed framework integrates several levels of QoS abstractions derived from user-perceived requirements. It also maps these abstractions to appropriate QoS resources that drive the development of mobile services that mitigate the effects of varying mobile environments.
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