Browsing by Author "Bouguettaya, Athman"
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- An Approach to Real Time Adaptive Decision Making in Dynamic Distributed SystemsAdams, Kevin Page (Virginia Tech, 2005-12-12)Efficient operation of a dynamic system requires (near) optimal real-time control decisions. Those decisions depend on a set of control parameters that change over time. Very often, the optimal decision can be made only with the knowledge of future values of control parameters. As a consequence, the decision process is heuristic in nature. The optimal decision can be determined only after the fact, once the uncertainty is removed. For some types of dynamic systems, the heuristic approach can be very effective. The basic premise is that the future values of control parameters can be predicted with sufficient accuracy. We can either predict those value based on a good model of the system or based on historical data. In many cases, the good model is not available. In that case, prediction using historical data is the only option. It is necessary to detect similarities with the current situation and extrapolate future values. In other words, we need to (quickly) identify patterns in historical data that match the current data pattern. The low sensitivity of the optimal solution is critical. Small variations in data patterns should affect minimally the optimal solution. Resource allocation problems and other "discrete decision systems" are good examples of such systems. The main contribution of this work is a novel heuristic methodology that uses neural networks for classifying, learning and detecting changing patterns, as well as making (near) real-time decisions. We improve on existing approaches by providing a real-time adaptive approach that takes into account changes in system behavior with minimal operational delay without the need for an accurate model. The methodology is validated by extensive simulation and practical measurements. Two metrics are proposed to quantify the quality of control decisions as well as a comparison to the optimal solution.
- Automatic Visualization of the Version history of a Software System in Three DimensionsAsokan, Ramya (Virginia Tech, 2003-09-21)Software changes constantly and continuously. It is often beneficial to record the progressive changes made to software, so that when any problems arise, it is possible to identify the change that might have caused the problem. Also, recording these changes enables recovery of the software as it was at any point of time. A version control system is used to track modifications to software. Version control systems (VCS) display when and where a change was made. In the case of multiple developers working on the same software system, version control systems also record which developer was responsible for the change. RCS, SCCS and CVS are examples of such version control systems, and they usually have a command-line interface. The widespread use of CVS has however given rise to a host of "CVS clients", which provide a two-dimensional graphical interface to CVS. While working with a version control system in two dimensions is a definite improvement over traditional command line interfaces, it is still not sufficient to display all the necessary information in a single view. Using three dimensions to display the information from a version control system like CVS is an effective and efficient way to represent multiple attributes in a single view. There are many advantages to using a third dimension for visualizing the version history and evolution of software. A three-dimensional visualization tool has been developed to provide insights into the structure and characteristics of the history of a software system. It demonstrates the benefits of three-dimensional visualization and illustrates a framework that can be used to automatically derive information from a version control system.
- Change Management of Long Term Composed ServicesLiu, Xumin (Virginia Tech, 2009-07-28)We propose a framework for managing changes in Long term Composed Services (LCSs). The key components of the proposed framework include a Web Service Change Management Language (SCML), change enactment, and change optimization. The SCML is a formal language to specify top-down changes. It is built upon a formal model which consists of a Web service ontology and a LCS schema. The Web service ontology gives a semantic description on the important features of a service, including functionality, quality, and context. The LCS schema gives a high-level overview of a LCS's key features. A top-down change is specified as the modification of a LCS schema in the first place. Change enactment is the process of reacting to a top-down change. It consists of two subcomponents, including change reaction and change verification. The change reaction component implements the proposed change operators by modifying a LCS schema and the membership of Web services. The change verification component ensures that the correctness of a LCS is maintained during the process of change reaction. We propose a set of algorithms for the processes of change reaction and verification. The change optimization component selects the Web services that participate in a LCS to ensure that the change has been reacted to in the best way. We propose a two-phase optimization process to select services using both service reputation and service quality. We present a change management system that implements the proposed approaches. We also conduct a set of simulations to assess the performance.
- Efficient Delivery of Web ServicesOuzzani, Mourad (Virginia Tech, 2004-01-16)This dissertation addresses issues for the efficient access to Web databases and services. We propose a distributed ontology for a meaningful organization of and efficient access to Web databases. Next, we dedicate most of our work on presenting a comprehensive query infrastructure for the emerging concept of Web services. The core of this query infrastructure is to enable the efficient delivery of Web services based on the concept of Quality of Web Service. Treating Web services as first class objects is a fundamental step towards achieving the envisioned Semantic Web. Semantics-aware processing of information requires intensive use of Web services. In our research, we propose a new query model where queries are resolved by combining Web service invocations. To efficiently deploy such scheme, we propose an optimization strategy based on aggregating Quality of Web service (QoWS) of different Web services. QoWS is adjusted through a dynamic rating scheme and multilevel matching. Web service rating provides an assessment of their behavior. The multilevel matching allows a larger solution space by enabling similar and partial answers.
- Enforcing Trade Secrets among Competitors on the Semantic WebMalik, Choudhry Muhammad Zaki (Virginia Tech, 2004-08-18)In this thesis, we present a novel approach for the preservation of trade secrets in a Business-to-Business (B2B) environment that involves trade among competitors. The Web provides a low cost medium for B2B collaborations. Information exchange may take place during such a collaboration. The exchanged information may be of a sensitive nature, forming a business trade secret. The open nature of the Web calls for techniques to prevent the disclosure of trade secrets. The emerging Semantic Web is expected to make the challenge more acute in terms of trade secret protection due to the automation of B2B interactions. In this thesis, the different businesses are represented by Web services on the envisioned Semantic Web. We propose a Peer-to-Peer (P2P) approach for preserving trade secrets in B2B interactions. We introduce a set of techniques based on data perturbation for preserving data privacy. The techniques presented in our thesis are implemented in WebBIS, a prototype for accessing e-business Web services. Finally, we conduct an extensive performance study (analytical and experimental) of the proposed techniques.
- A Foundational Framework for Service Query OptimizationYu, Qi (Virginia Tech, 2008-07-30)In this dissertation, we present a novel foundational framework that lays out a theoretical underpinning for the emerging services science. The proposed framework provides disciplined and systematic support for efficient access to Web services' functionalities. The key components of the proposed framework centers around a novel service model that provides a formal abstraction of the Web services within an application domain. A service calculus and a service algebra are defined to facilitate users in accessing services via declarative service queries. We provide the implementation of the service algebra. This enables the generation of Service Execution Plans (SEPs) that can be used by users to directly access services. We present an optimization algorithm to efficiently select the SEPs with the best QoWS. We then propose a multi-objective optimization approach that releases users from the tedious weight assigning process. We develop service skyline computation techniques that return a set of most interesting SEPs. The service skyline guarantees to include the user desired SEPs. We further explore a set of novel heuristics for computing service skylines over sets of services. This enables users to efficiently and optimally access multiple services simultaneously as an integrated service package. Finally, we consider the performance fluctuation of service providers due to the dynamic service environment. We propose an uncertain QoWS model and a novel concept called p-dominant service skyline. We develop new indexing structures and algorithms to efficiently compute the p-dominant service skyline. We derive analytical models and conduct extensive sets of experiments to evaluate the proposed framework and service query optimization algorithms.
- Managing Changes to Service Oriented EnterprisesAkram, Mohammad Salman (Virginia Tech, 2005-05-23)In this thesis, we present a framework for managing changes in service oriented enterprises (SOEs). A service oriented enterprise outsources and composes its functionality from third-party Web service providers. We focus on changes initiated or triggered by these member Web services. We present a taxonomy of changes that occur in service oriented enterprises. We use a combination of several types of Petri nets to model the triggering changes and ensuing reactive changes. The techniques presented in our thesis are implemented in WebBIS, a prototype for composing and managing e-business Web services. Finally, we conduct an extensive simulation study to prove the feasibility of the proposed techniques.
- Multi-channel Mobile Access to Web ServicesYang, Xu (Virginia Tech, 2007-11-26)To support wireless-oriented services, a new generation of Web services called Mobile services (M-services) has emerged. M-services provide mobile users access to services through wireless networks. One of the important issues in M-service environment is how to discover and access M-services efficiently. In this dissertation, we propose time and power efficient access methods for M-services. We focus on methods for accessing broadcast based M-services from multiple wireless channels. We first discuss efficient access methods in data-oriented wireless broadcast systems. We then discuss how to extend current wireless broadcast systems to support simple M-services. We present a novel infrastructure that provides a multi-channel broadcast framework for mobile users to effectively discover and access composite M-services. Multi-channel algorithms are proposed for efficiently accessing composite services. We define a few semantics that have impact on access efficiency in the proposed infrastructure. We discuss semantic access to composite services. Broadcast channel organizations suitable for discovering and accessing composite services are proposed. We also derive analytical models for these channel organizations. To provide practical study for the proposed infrastructure and access methods, a testbed is developed for simulating accessing M-services in a broadcast-based environment. Extensive experiments have been conducted to study the proposed access methods and broadcast channel organizations. The experimental results are presented and discussed.
- Performance Analysis of Algorithms for Supporting Disconnected Write Operations in Wireless Web EnvironmentsPhan, Ngoc Anh (Virginia Tech, 1999-11-19)A mobile user may voluntarily disconnect itself from the web server to save battery life and also to avoid the high communication price. To allow web pages to be updated while the mobile user is disconnected from the web server, updates can be staged in the mobile unit and propagated back to the web server upon reconnection. In this thesis, we investigate methods for supporting disconnected write operations and develop a performance model which helps identify the optimal length of the disconnection period under which the cost of update propagation is minimized. We validate the analytic model with simulation in the thesis. We also show how the result can be applied to real-time web applications with a deadline requirement to propagate updates of web pages. The analysis result is particularly applicable to web applications which allow wireless mobile users to modify web contents while on the go. The algorithms that we have developed can be generally applied to other data items such as files and databases.
- Reputation-based Trust Framework for Service Oriented EnvironmentsMalik, Zaki (Virginia Tech, 2008-10-24)We investigate the problem of establishing trust in service-oriented environments. We focus on providing a reputation framework that would enable trust-based interactions with and amongst Web services. We define methods for the creation of reputation information, its collection, and assessment that are robust in the face of a variety of attacks. Our framework (denoted RATEWeb) supports a cooperative model in which Web services share their experiences of the service providers with their peers through feedback ratings. The different ratings are aggregated to derive a service provider's reputation. This in turn is used to evaluate trust. For situations where rater feedbacks are scarce, we use statistical forecasting (particularly, a Hidden Markov Model) to ascertain trust. The approaches and techniques developed under the RATEWeb framework facilitate the optimal selection and/or composition of Web services based on service reputations. We conduct an extensive performance study (analytical and experimental) to assess the fairness and accuracy of the proposed techniques.
- Semantic Web Enabled Composition of Web ServicesMedjahed, Brahim (Virginia Tech, 2004-01-19)In this dissertation, we present a novel approach for the automatic composition of Web services on the envisioned Semantic Web. Automatic service composition requires dealing with three major research thrusts: semantic description of Web services, composability of participant services, and generation of composite service descriptions. This dissertation deals with the aforementioned research issues. We first propose an ontology-based framework for organizing and describing semantic Web services. We introduce the concept of community to cluster Web services based on their domain of interest. Each community is defined as an instance of an ontology called community ontology. We then propose a composability model to check whether semantic Web services can be combined together, hence avoiding unexpected failures at run time. The model defines formal safeguards for meaningful composition through the use of composability rules. We also introduce the notions of composability degree and tau-composability to cater for partial and total composability. Based on the composability model, we propose a set of algorithms that automatically generate detailed descriptions of composite services from high-level specifications of composition requests. We introduce a Quality of Composition (QoC) model to assess the quality of the generated composite services. The techniques presented in this dissertation are implemented in WebDG, a prototype for accessing e-government Web services. Finally, we conduct an extensive performance study (analytical and experimental) of the proposed composition algorithms.
- Service-based analysis of biological pathwaysZheng, George; Bouguettaya, Athman (2009-10-01)Background Computer-based pathway discovery is concerned with two important objectives: pathway identification and analysis. Conventional mining and modeling approaches aimed at pathway discovery are often effective at achieving either objective, but not both. Such limitations can be effectively tackled leveraging a Web service-based modeling and mining approach. Results Inspired by molecular recognitions and drug discovery processes, we developed a Web service mining tool, named PathExplorer, to discover potentially interesting biological pathways linking service models of biological processes. The tool uses an innovative approach to identify useful pathways based on graph-based hints and service-based simulation verifying user's hypotheses. Conclusion Web service modeling of biological processes allows the easy access and invocation of these processes on the Web. Web service mining techniques described in this paper enable the discovery of biological pathways linking these process service models. Algorithms presented in this paper for automatically highlighting interesting subgraph within an identified pathway network enable the user to formulate hypothesis, which can be tested out using our simulation algorithm that are also described in this paper.
- Web Service MiningZheng, George (Virginia Tech, 2009-02-04)In this dissertation, we present a novel approach for Web service mining. Web service mining is a new research discipline. It is different from conventional top down service composition approaches that are driven by specific search criteria. Web service mining starts with no such criteria and aims at the discovery of interesting and useful compositions of existing Web services. Web service mining requires the study of three main research topics: semantic description of Web services, efficient bottom up composition of composable services, and interestingness and usefulness evaluation of composed services. We first propose a Web service ontology to describe and organize the constructs of a Web service. We introduce the concept of Web service operation interface for the description of shared Web service capabilities and use Web service domains for grouping Web service capabilities based on these interfaces. We take clues from how Nature solves the problem of molecular composition and introduce the notion of Web service recognition to help devise efficient bottom up service composition strategies. We introduce several service recognition mechanisms that take advantage of the domain-based categorization of Web service capabilities and ontology-based description of operation semantics. We take clues from the drug discovery process and propose a Web service mining framework to group relevant mining activities into a progression of phases that would lead to the eventual discovery of useful compositions. Based on the composition strategies that are derived from recognition mechanisms, we propose a set of algorithms in the screening phase of the framework to automatically identify leads of service compositions. We propose objective interestingness and usefulness measures in the evaluation phase to narrow down the pool of composition leads for further exploration. To demonstrate the effectiveness of our framework and to address challenges faced by existing biological data representation methodologies, we have applied relevant techniques presented in this dissertation to the field of biological pathway discovery.