VTechWorks Repository :: Browsing by Author "Balci, Osman"

Browsing by Author "Balci, Osman"

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Analysis and Modeling of World Wide Web Traffic
Abdulla, Ghaleb (Virginia Tech, 1998-04-27)
This dissertation deals with monitoring, collecting, analyzing, and modeling of World Wide Web (WWW) traffic and client interactions. The rapid growth of WWW usage has not been accompanied by an overall understanding of models of information resources and their deployment strategies. Consequently, the current Web architecture often faces performance and reliability problems. Scalability, latency, bandwidth, and disconnected operations are some of the important issues that should be considered when attempting to adjust for the growth in Web usage. The WWW Consortium launched an effort to design a new protocol that will be able to support future demands. Before doing that, however, we need to characterize current users' interactions with the WWW and understand how it is being used. We focus on proxies since they provide a good medium or caching, filtering information, payment methods, and copyright management. We collected proxy data from our environment over a period of more than two years. We also collected data from other sources such as schools, information service providers, and commercial aites. Sampling times range from days to years. We analyzed the collected data looking for important characteristics that can help in designing a better HTTP protocol. We developed a modeling approach that considers Web traffic characteristics such as self-similarity and long-range dependency. We developed an algorithm to characterize users' sessions. Finally we developed a high-level Web traffic model suitable for sensitivity analysis. As a result of this work we develop statistical models of parameters such as arrival times, file sizes, file types, and locality of reference. We describe an approach to model long-range and dependent Web traffic and we characterize activities of users accessing a digital library courseware server or Web search tools. Temporal and spatial locality of reference within examined user communities is high, so caching can be an effective tool to help reduce network traffic and to help solve the scalability problem. We recommend utilizing our findings to promote a smart distribution or push model to cache documents when there is likelihood of repeat accesses.
Analysis of networks with dynamic topologies
Moose, Robert Lewis (Virginia Polytechnic Institute and State University, 1987)
Dynamic hierarchical networks represent an architectural strategy for employing adaptive behavior in applications sensitive to highly variable external demands or uncertain internal conditions. The characteristics of such architectures are described, and the significance of adaptive capability is discussed. The necessity for assessing cost/benefit tradeoffs leads to the use of queueing network models. The general model, a network of M/M/1 queues in a random environment, is introduced and then is simplified so that the links may be treated as isolated M/M/1 queues in a random environment. This treatment yields a formula for approximate mean network delay by combining matrix-geometric results (mean queue length and mean delay) for the individual links. Conditions under which the analytic model is considered valid are identified through comparison with a discrete event simulation model. Last, performance of the dynamic hierarchy is compared with that of the static hierarchy. This comparison establishes conditions for which the dynamic architecture enables performance equal or nearly equal to performance of the static architecture.
Animations and Interactive Material for Improving the Effectiveness of Learning the Fundamentals of Computer Science
Gilley, William (Virginia Tech, 2001-05-08)
Due to the rapid proliferation of the World Wide Web (WWW) in recent years, many educators are now seeking to improve the effectiveness of their instruction by providing interactive, web-based course material to their students. The purpose of this thesis is to document a set of eight online learning modules created to improve the effectiveness of learning the fundamentals of Computer Science. The modules are as follows: • Algorithms - Definition and specification of algorithms, with a comparison and analysis of several sorting algorithms as examples. • Artificial Intelligence - Overview of current applications in this discipline. • Data Structures - Explanation of basic data structures, including an introduction to computer memory and pointers, and a comparison of logical and physical representations of commonly used data structures. • Machine Architecture - Explanation of data storage, gates and circuits, and the central processing unit. • Number Systems - Discussion of number representation and arithmetic in number systems other than the decimal number system, with a focus on binary numbers and binary arithmetic. • Operating Systems - Explanation of the purpose of operating systems and the major components that make up an operating system. • Programming Languages - Explanation of the fundamental concepts in procedural programming languages. • Software Engineering - Introduction to software life cycle models and an overview of the procedural and object-oriented paradigms. Each module consists of a set of lessons and review questions written in HyperText Markup Language (HTML). Embedded in these pages are various interactive components implemented as Flash animations or Java applets. The modules currently reside on the Computer Science courseware server of Virginia Polytechnic Institute and State University (Virginia Tech) and can be viewed at the following WWW site: http://courses.cs.vt.edu/csonline/
Application of the Analytic Hierarchy Process to Complex System Design Evaluation
Talbert, Michael L.; Balci, Osman; Nance, Richard E. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1994-06-01)
This paper examines the use of the Analytic Hierarchy Process (AHP) to weight indicators used in the evaluation of complex systems designs which involve software, hardware, and humanware. Since such a comprehensive easily include hundreds of system quality indicators, evaluators need a technique to ensure the identification and emphasis of salient indicators in the determination of the quality of the design. The AHP is a popular technique for determining relative worth among a set of elements. In the present work, we introduce AHP with a simple example, then illustrate the application of the AHP to design evaluation using a subset of indicators from the human component of a system. We note in some detail issues which require added attention when applying AHP to this domain. The issues include indicator selection, dealing with large numbers of indicators, incorporating group judgements, and conflict resolution. We found AHP to be an effective tool for use in assigning weights criticality in indicator-based design evaluation, and propose elements of an environment in which the use of AHP is easily incorporated.
Assessing Agile Methods: Investigating Adequacy, Capability, and Effectiveness (An Objectives, Principles, Strategies Approach)
Soundararajan, Shvetha (Virginia Tech, 2013-06-10)
Agile methods provide an organization or a team with the flexibility to adopt a selected subset of principles and practices based on their culture, their values, and the types of systems that they develop. More specifically, every organization or team implements a customized agile method, tailored to better accommodate its needs. However, the extent to which a customized method supports the organizational objectives, i.e. the 'goodness' of that method, should be demonstrable. Existing agile assessment approaches focus on comparative analyses, or are limited in scope and application. In this research, we propose a systematic, comprehensive approach to assessing the 'goodness' of agile methods. We examine an agile method based on (1) its adequacy, (2) the capability of the organization to support the adopted principles and strategies specified by the method, and (3) the method's effectiveness. We propose the Objectives, Principles and Strategies (OPS) Framework to guide our assessment process. The Framework identifies (a) objectives of the agile philosophy, (b) principles that support the objectives and (c) strategies that implement the principles. It also defines (d) linkages that relate objectives to principles, and principles to strategies, and finally, (e) indicators for assessing the extent to which an organization supports the implementation and effectiveness of those strategies. The propagation of indicator values along the linkages provides a multi-level assessment view of the agile method. In this dissertation, we present our assessment methodology, guiding Framework, validation approach, results and findings, and future directions.
A Campus Situational Awareness and Emergency Response Management System Architecture
Chigani, Amine (Virginia Tech, 2011-04-06)
The history of university, college, and high school campuses is eventful with man-made tragedies ensuing a tremendous loss of life. Virginia Tech's April 16 shooting ignited the discussion about balancing openness and safety in open campus environments. Existing campus safety solutions are characterized by addressing bits and pieces of the problem. The perfect example is the recent influx in demand for Electronic Notification Systems (ENS) by many educational institutions following the tragedies at Virginia Tech and Northern Illinois University. Installing such systems is important, as it is an essential part of an overall solution. However, without a comprehensive, innovative understanding of the requirements for an institution-wide solution that enables effective security control and efficient emergency response, the proposed solutions will always fall short. This dissertation describes an architecture for SINERGY (campuS sItuational awareNess and Emergency Response manaGement sYstem) – a Service-Oriented Architecture (SOA)-based network-centric system of systems that provides a comprehensive, institution-wide, software-based solution for balancing safety and openness on any campus environment. SINERGY architecture addresses three main capabilities: Situational awareness (SA), security control (SC), and emergency response management (ERM). A safe and open campus environment can be realized through the development of a network-centric system that enables the creation of a COP of the campus environment shared by all campus entities. Having a COP of what goes on campus at any point in time is key to enabling effective SC measures to be put in place. Finally, common SA and effective SC lay the foundation for an efficient and successful ERM in the case of a man-made tragedy. Because this research employs service orientation principles to architect SINERGY, this dissertation also addresses a critical area of research with regards to SOA; that area is SOA security. Security has become a critical concern when it comes to SOA-based network-centric systems of systems due the nature of business practices today, which emphasize dynamic sharing of information and services among independent partners. As a result, the line between internal and external organization networks and services has been blurred making it difficult to assess the security quality of SOA environments. In order to do this evaluation effectively, a hierarchy of security indicators is developed. The proposed hierarchy is incorporated in a well-established evaluation methodology to provide a structured approach for assessing the security of an SOA-based network-centric system of systems. Another area of focus in this dissertation is the architecting process. With the advent of potent network technology, software/system engineering has evolved from a traditional platform-centric focus into a network-centric paradigm where the “system of systems” perspective has been the norm. Under this paradigm, architecting has become a critical process in the life cycle of software/system engineering. The need for a structured description of the architecting process is undeniable. This dissertation fulfills that need and provides a structured description of the process of architecting a software-based network-centric system of systems. The architecting process is described using a set of goals that are specific to architecting, and the associated specific practices that enable the realization of these goals. The architecting process description presented herein is intended to guide the software/system architects.
CandyFactory: Cloud-Based Educational Game for Teaching Fractions
Ying, Tiancheng (Virginia Tech, 2019-06-17)
Nowadays cross platform software development is more expensive than ever before in terms of time and effort. Meantime with increasing number of personal devices, it is harder for local applications to synchronize and connect to the Internet. In terms of educational games, they can be divided into "local educational game" and "web educational game." "Local game" indicates the ones either on tablets, mobile devices or PC, which is an application on the corresponding platform. This kind of game mostly does not have backend support nor cross platform features such as the iPad version of CandyFactory. For one specific game, if the developer wants it to run on iPad and Android tablets, they need to develop two applications based on corresponding development framework, which is time and effort consuming. "Web game" indicates the ones on websites, which support cross platforms, but do not have backend support. Usually they are pure JavaScript or flash games with no backend recording the performances and the achievements. Software development for each individual platform is time and effort consuming. In order to achieve cross platform development, many programming languages and platforms like Java, Python, and JVM appear. Among all the cross platform approaches, cloud-based software development is the most universal solution to this problem. With web browsers built into every operating system, cloud software can be compatible with almost any device. Moreover, "Software-as-a-Service" (SaaS) is becoming a new software engineering paradigm and cloud-based software development is more popular because of its flexible scalability and cross platform features. In this thesis, we create a cloud-based educational game, CandyFactory, based on an iPad version of CandyFactory, and add backend to it to record user performance as well as achievements. Firstly, we re-develop the whole game from the iOS platform to the cloud-based Java EE platform. Secondly, we add new features to improve the game play such as ruler functionality and achievements animation. Thirdly, we add backend support to CandyFactory, including user account creation, course creation and performance report generation. With this functionality, teachers can monitor their students' performances and generate course reports. Moreover, teachers can view a specific student's report in order to provide more specific and effective help to their students. Lastly, with the advantages of cloud-based software development, we can update the whole application at any time without forcing the user to reinstall the update or re-download the game. With the hot update, the cloud-based CandyFactory is highly maintainable. The cloud-based CandyFactory runs on any computer that supports minimum 1024x768 screen resolution. The computer could be iPads, Android or Microsoft tablets, Windows or Mac laptops and desktops, and any other computer with a web browser. The advantages of cloud-based educational games over local educational games and web educational games are: firstly, they have cross platform features; secondly, they have backend data collection support; thirdly, they are consistent even if users log in with different computers, their game record and history will always be the same; lastly, the teacher can always keep track of his/her students' performance and provide more specific help and feedback.
Cellular and functional production environments: design methodology and comparison
Sarper, Hüseyin (Virginia Polytechnic Institute and State University, 1988)
A hybrid methodology was developed to fairly compare functional and cellular production environments with respect to the production of machined parts which constitute the indivisible components of some final products. The methodology provides a means of designing each production environment at the lowest possible cost and then comparing the two environments with respect to cost and non-cost performance measures. The results show that the long-held belief that the cellular manufacturing or group technology method of production may be superior to that of the traditional functional or job shop layout may not be correct. A detailed comparison using four problem sets with different job and machine mixes failed to indicate a clear case in which the cellular environment performed better than the functional. The methodology consists of two stages. Stage one has six hierarchical steps which systematically determine machine requirements and layout planning of each environment through mathematical modelling. External and internal operation constraints and inputs such as stochastic daily demand and operation times were considered. Stochastic programming was used in handling uncertain daily demand and operation times by specifying a desired minimum probability of meeting the demand for each job type in both environments. The MPSIII package was used in solving large mixed integer problems that resulted once nonlinear terms, due to the chance-constrained nature of the segments of the models, were linearized. Because of the large problem sizes, MPSIII input files had to be created using FORTRAN codes. In stage two, the SIMAN simulation language was used to determine the feasibility of stage one decisions and to obtain other system information. In simulation, some approximations were made to implement stage one decisions. For example, jobs received an average processing time in each operation class area rather than the exact operation time of the specific machine type to which the jobs were assigned in stage one. The effect of material handling distances and the use of limited number of work-in-process carriers were considered. Although the methodology was mainly developed for the comparison of the two production environments, it is readily usable for individual design of either production environment. In addition to the two main stages of development, this research also required the development of two other procedures: unitizing daily demands and the modifying the previously available job/cell grouping methods.
The Claims Library Capability Maturity Model: Evaluating a Claims Library
Allgood, Christian (Virginia Tech, 2004-05-12)
One of the problem that plagues Human-Computer Interaction (HCI) software is its development cost. Many software companies forego the usability engineering aspect of their projects due to the time required to design and test user interfaces. Unfortunately, there is no "silver bullet" for user interface design and implementation because they are inherently difficult tasks. As computers are moving off the desktop, the greatest challenge for designers will be integrating these systems seamlessly into our everyday lives. The potential for reuse in user interfaces lies in reducing the time and effort required for this task, without sacrificing design quality. In this work we begin with an iterative development cycle for a claims library based on prominent literature within the HCI and software engineering fields. We constructed the Claims Library to be a repository of potentially reusable notification system claims. We examine the library through theoretical and practical perspectives. The theoretical perspective reveals tradeoffs in the initial implementation that relate to Krueger's taxonomy of reuse. The practical perspective stems from experience in designing and conducting usability testing for an in-vehicle input device using the Claims Library. While valuable, these examinations did not provide a distinct method of improving the library. Expecting to uncover a specific diagnosis for the problems in the library, it was unclear how they should be approached with further development efforts. With this realization, we saw that a more important and immediate contribution would not be another iteration of the Claims Library design. Rather, a clarification of the underlying theory that would better inform future systems development seemed a more urgent and worthy use of our experience. This clarification would need to have several characteristics to include: composed of a staged or prioritized architecture, represents an ideal model grounded in literature, and possesses intermediate development objectives and assessment points. As a solution, we propose the Claims Library Capability Maturity Model (CL-CMM), based on the theoretical deficiencies that should guide development of a claims library, as noted in the two evaluations. This thesis delivers a five-stage model to include process areas, goals, and practices that address larger threads of concern. Our capability maturity model is patterned after models in software engineering and human resource management. We include a full description of each stage, a gap analysis method of appraisal, and an example of its use. Several directions for future work are noted that are necessary to continue development and validation of the model.
Class hierarchy design for space time problems
Chopra, Sanjay (Virginia Tech, 1995-07-06)
The purpose of the project is to design a class hierarchy that will aid in the development of simulations for certain space time problems. The class hierarchy and the problem domain to which it applies are illustrated by considering simulations of three representative problems: a pool game; a collision detection system for robot arms; an automated highway system. The emphasis in the simulations is on the class hierarchy. The class hierarchy contains base classes to model objects, space, time and interactions among objects. These classes could be applied to other similar problems in the problem domain. For example the class objects help to model various objects like cars, pool balls, robots, trains, birds etc. Class space allows the user to subdivide the problem space into smaller dynamic sub-spaces. The user can define rules to decompose the space into 'n’ smaller spaces when there are more than 'x' objects in the space.
A Client-Server Architecture for Collection of Game-based Learning Data
Jones, James R. (Virginia Tech, 2015-01-27)
Advances in information technology are driving massive improvement to the education industry. The ubiquity of mobile devices has triggered a shift in the delivery of educational content. More lessons in a wide range of subjects are being disseminated by allowing students to access digital materials through mobile devices. One of the key materials is digital-based educational games. These games merge education with digital games to maximize engagement while somewhat obfuscating the learning process. The effectiveness is generally measured by assessments, either after or during gameplay, in the form of quizzes, data dumps, and/or manual analyses. Valuable gameplay information lost during the student's play sessions. This gameplay data provides educators and researchers with specific gameplay actions students perform in order to arrive at a solution, not just the correctness of the solution. This problem illustrates a need for a tool, enabling educators and players to quickly analyze gameplay data. in conjunction with correctness in an unobtrusive manner while the student is playing the game. This thesis describes a client-server software architecture that enables the collection of game-based data during gameplay. We created a collection of web services that enables games to transmit game-data for analysis. Additionally, the web application provides players with a portal to login and view various visualization of the captured data. Lastly, we created a game called "Taffy Town", a mathematics-based game that requires the player to manipulate taffy pieces in order to solve various fractions. Taffy Town transmits students' taffy transformations along with correctness to the web application. Students are able to view several dynamically created visualizations from the data sent by Taffy Town. Researchers are able to log in to the web application and see the same visualizations, however, aggregated across all Taffy Town players. This end-to-end mapping of problems, actions, and results will enable researchers, pedagogists, and teachers to improve the effectiveness of educational games.
A Cloud-based Software System for online Multimedia Examinations
Tao, Congwu (Virginia Tech, 2016-03-22)
With the advancement in information technology, online assessments are getting more attention and online examinations are regarded as important parts of online learning. Online examinations can be easily taken by remote students, help the students get exam results quickly and save their time; online examinations also aid instructors in collecting students' exam answers and generating the exam reports effectively. In addition, online examinations can help reduce cost and save trees for our world. Multimedia elements like images, graphics, video and audio have been widely integrated into online learning environments. They not only help instructors design more engaging online learning content, but also help provide more interactive and pleasant learning experience for learners. However, integrating multimedia elements into online examination systems is rarely reported. Multimedia elements generally consume amounts of computing resources in a separated software system running on a single computer. "Software-as-a-Service (SaaS)" has become a new software paradigm and cloud-based software systems are becoming more attractive due to their dynamic scalability and effective usage of computing resources. Yet, how to effectively integrate multimedia elements into a cloud-based software system for online examinations is not significantly investigated. Although a variety of online-assessment tools have been developed, few of them adopt the "Software-as-a-Service (SaaS)" paradigm and most of them focus on the assessment in a specific domain or an application area with short of multimedia elements. There is a lack of a comprehensive software solution for online multimedia examinations. This thesis tries to utilize the "Software-as-a-Service (SaaS)" paradigm, design and develop a cloud-bAsed softwaRe systEm for oNline multimediA examinationS (ARENAS), and explore a comprehensive software solution for the online assessment field. ARENAS employs a multi-tiered client-server architecture and includes five subsystem modules: user module, question repository module, exam module, exam report module and configuration module. The developed cloud-based software system can present online questions with multimedia elements, and also support a myriad of question types, flexible accounts to the exam-takers, randomized question order in an online exam, flexible grading mechanisms, and analytical exam reports. For instructors, the developed system can help design more engaging online questions; for exam-takers, the developed system can help provide more user-friendly experience; for other educators and researchers, the design and development processes of ARENAS can be taken as a reference to designing and developing other large-scale cloud-based educational software systems.
A Cloud-Based Visual Simulation Environment for Traffic Networks
Onder, Sait Tuna (Virginia Tech, 2018-06-19)
Cloud-based Integrated Development Environments (IDEs) are highly complex systems compared to stand-alone IDEs that are installed on client devices. Today, the visual simulation environments developed as services on the cloud can offer similar features as client-based IDEs thanks to the advancements to the cloud technologies. However, most of the existing visual simulation tools are developed for client-based systems. Moving towards the cloud for visual simulation environments can provide better collaboration for simulation developers, easy access to the software, and less client hardware dependency. Proper guidance for the development of visual simulation tools can help researchers to develop their tools as a service on the cloud. This thesis presents a Cloud-based visuAl simulatioN enVironment for trAffic networkS (CANVAS), providing a framework that tackles challenges on the cloud-based visual simulation tools. CANVAS offers a set of tools for the composition and visualization of simulation models for the traffic network problem domain. CANVAS uses an asynchronous visualization protocol with efficient resource utilization on the server, enabling concurrent usage of the IDE. The simulation is executed on the server while the visualization is processed on the client-device within web browsers enabling execution-heavy simulations to thin clients. The component-based architecture of CANVAS offers a fully decoupled system that provides easier development and maintenance. The architecture can be used for the development of other cloud-based visual simulation IDEs. The CANVAS design and asynchronous visualization protocol show that advanced visualization capabilities can be provided to the client without depending on the client hardware.
Combined correlation induction strategies for designed simulation experiments
Kwon, Chimyung (Virginia Tech, 1991-01-07)
This dissertation deals with variance reduction techniques (VRTs) for improving the reliability of the estimators of interest through a controlled laboratory-like simulation experiment. This research concentrates on correlation methods of VRTs which include common random numbers, antithetic variates and control variates. The basic idea of these methods is to utilize the linear correlation either between the responses or between the response and control variates in order to reduce the variance of estimators of certain system parameters. Combining these methods, we develop procedures for estimating a system parameter of interest. First, we develop three combined methods utilizing antithetic variates and control variates for improving the estimation of the mean response in a single population model. We explore how these methods may reduce the variance of the estimator of interest. A combined method (Combined Method 1) using antithetic variates for the non-control variate stochastic components and independent streams for the control variates yields better results than by applying methods of either antithetic variates or control variates individually for several selected models. Second, we develop variance reduction techniques for improving the estimation of the model parameters in a multipopulation simulation model. We extend Combined Method 1 showing good performance in estimating the mean response of a single population model to the multipopulation context with independent simulation runs across design points. We also develop another extension of Combined Method 1 that incorporates the Schruben-Margolin method to estimate the parameters of a multipopulation model. Under certain conditions, this method is superior to the Schruben-Margolin method. Finally, we propose a new approach (Extended Schruben-Margolin Method) utilizing the control variates under the Schruben-Margolin strategy for improving the estimation in a first-order linear model. Extended Schruben-Margolin Method yields better results than the Schruben-Margolin method in estimating the model parameters of interest.
A Common Software Development Framework For Coordinating Usability Engineering and Software Engineering Activities
Pawar, Sourabh A. (Virginia Tech, 2004-05-10)
Currently, the Usability Engineering (UE) and Software Engineering (SE) processes are practiced as being independent of each other. However, several dependencies and constraints exist between the interface specifications and the functional core, which make coordination between the UE and the SE teams crucial. Failure of coordination between the UE and SE teams leads to software that often lacks necessary functionality and impedes user performance. At the same time, the UE and SE processes cannot be integrated because of the differences in focus, techniques, and terminology. We therefore propose a development framework that incorporates SE and UE efforts to guide current software development. The framework characterizes the information exchange that must exist between the UE and SE teams during software development to form the basis of the coordinated development framework. The UE Scenario-Based Design (SBD) process provides the basis for identifying UE activities. Similarly, the Requirements Generation Model (RGM), and Structured Analysis and Design are used to identify SE activities. We identify UE and SE activities that can influence each other, and identify the high-level exchange of information that must exist among these activities. We further examine these interactions to gain a more in-depth understanding as to the precise exchange of information that must exist among them. The identification of interacting activities forms the basis of a coordinated development framework that incorporates and synchronizes the UE and SE processes. An examination of the Incremental and Spiral models as they relate to the SBD is provided, and outlines how our integration framework can be composed. Using the results of and insights gained from our research, we also suggest additional avenues for future work.
Comparative Assessment of Network-Centric Software Architectures
Krishnamurthy, Likhita (Virginia Tech, 2006-05-01)
The purpose of this thesis is to characterize, compare and contrast four network-centric software architectures, namely Client-Server Architecture (CSA), Distributed Objects Architecture (DOA), Service-Oriented Architecture (SOA) and Peer-to-Peer Architecture (PPA) and seven associated frameworks consisting of .NET, Java EE, CORBA, DCOM, Web Services, Jini and JXTA with respect to a set of derived criteria. Network-centric systems are gaining in popularity as they have the potential to solve more complex problems than we have been able to in the past. However, with the rise of SOA, Web Services, a set of standards widely used for implementing service-oriented solutions, is being touted as the "silver bullet" to all problems afflicting the software engineering domain with the danger of making other architectures seem obsolete. Thus, there is an urgent need to study the various architectures and frameworks in comparison to each other and understand their relative merits and demerits for building network-centric systems. The architectures studied here were selected on the basis of their fundamentality and generality. The frameworks were chosen on the basis of their popularity and representativeness to build solutions in a particular architecture. The criteria used for comparative assessment are derived from a combination of two approaches — by a close examination of the unique characteristics and requirements of network-centric systems and then by an examination of the constraints and mechanisms present in the architectures and frameworks under consideration that may contribute towards realizing the requirements of network-centric systems. Not all of the criteria are equally relevant for the architectures and frameworks. Some, when relevant, are relevant in a different sense from one architecture (or framework) to another. One of the conclusions that can be drawn from this study is that the different architectures are not completely different from each other. In fact, CSA, DOA and SOA are a natural evolution in that order and share several characteristics. At the same time, significant differences do exist, so it is clearly possible to judge/differentiate one from the other. All three architectures can coexist in a single system or system of systems. However, the advantages of each architecture become apparent only when they are used in their proper scope. At the same time, a sharp difference can be perceived between these three architectures and the peer-to-peer architecture. This is because PPA aims to solve a totally different class of problems than the other three architectures and hence has certain unique characteristics not observed in the others. Further, all of the frameworks have certain unique architectural features and mechanisms not found in the others that contribute towards achieving network-centric quality characteristics. The two broad frameworks, .NET and Java EE offer almost equivalent capabilities and features; what can be achieved in one can be achieved in the other. This thesis deals with the study of all the four architectures and their related frameworks. The criteria used, while fairly comprehensive, are not exhaustive. Variants of the fundamental architectures are not considered. However, system/software architects seeking an understanding of the tradeoffs involved in using the various architectures and frameworks and their subtle nuances should benefit considerably from this work.
A Comparison of Selected Conceptual Frameworks for SimulationModeling
Derrick, Emory Joseph; Balci, Osman; Nance, Richard E. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1989)
The purpose of this paper is compare 13 Conceptual Frameworks (CFs) selected from among several catagories of applicability to discrete-event simulation modeling. Each CF is briefly reviewed to provide the background information required for the comparison. Based on the insights gained in applying the CFs to the modeling complex traffic intersection system, the CFs are compared to their distinct characteristics and capabilities. Comparative comments are grouped according to the design guidance and implementation guidance features of the CFs. Conclusions highlight the inadequacies of the CFs and the importance of research in CF development.
A Conceptual Framework for Specification of Network-Centric System Architectures
Churbanau, Dzmitry (Virginia Tech, 2010-05-03)
Software-based system architecture has been recognized as a foundation laying out the underpinnings that are critically important for successful engineering of large-scale complex systems. In recent years, architecting has played a more crucial role in engineering network-centric system of systems. The software paradigm has been shifting from treating software as a product (SaaP) to treating software as a service (SaaS). SaaS is also referred to as the Cloud Computing, where the term "cloud" is used as a metaphor for "network". As the complexity of the architecture of network-centric software-based system of systems has increased, the description of such architecture has posed significant technical challenges. The U.S. Department of Defense (DoD) has developed the DoD Architecture Framework [DoDAF 2009a, DoDAF 2009b] for describing system architectures. IEEE proposes a Recommended Practice for Architectural Description of Software-Intensive Systems [IEEE 2000]. SEI provides high-level guidelines for Documenting Software Architectures [Clements et al 2003]. However, all of the diagrams proposed by DoD, IEEE, and SEI are two-dimensional static graphical and textual representations that do not reveal the dynamic characteristics of a system architecture. This thesis presents a conceptual framework (CF) for specifying the architecture of a network-centric software-based system of systems. The developed CF provides the beginning part of a larger research effort. The main goal of the overall research is to employ the automation-based software paradigm and to automatically generate a visual simulation model of a system architecture, with which experiments can be conducted to assess the dynamic characteristics of that architecture. The CF, developed in the research described herein, enables the automatic generation of a visual simulation model representing a system architecture. The proposed CF is evaluated in half a dozen case studies to demonstrate that it provides the necessary elements for automatic generation of a simulation model as the description of a complex system of systems architecture.
Conceptual frameworks for discrete event simulation modeling
Derrick, Emory Joseph (Virginia Tech, 1988-08-05)
This thesis examines those aspects of simulation with digital computers which concern the use of conceptual frameworks (CFs) for the design and implementation of a model. A literature review of CFs which are in common use is conducted. These CFs are applied to a complex modeling problem, a traffic intersection system. A comparative review of the CFs is given based upon the lessons learned from the above applications, and a taxonomy is developed. The research clarifies the differences that exist among the myriad of CFs in use today. In particular, the comparative review highlights the significant CF features that are necessary for successful model representation of discrete-event systems. The taxonomy provides a useful and meaningful classification of CFs and produces insights in to the conceptual relationships that exist among them. The characteristics of CFs that are desired to enable the development of model specifications that are analyzable, domain independent, and fully translatable are identified. The roles of CFs are better understood and specific potential directions for future research are pinpointed.
Credibility Assessment of Simulation Results: The State of the Art
Balci, Osman (Department of Computer Science, Virginia Polytechnic Institute & State University, 1986)
The purpose of this paper is to provide a state-of-the-art survey of credibility assessment of simulation results and suggest some future research directions. A hierarchy of the credibility assessment is introduced and the state-of-the-art survey is presented with respect to this hierarchy. A glossary is provided to alleviate the lack of standard terminology. The future research calls upon looking at the global picture when conducting a simulation study and being concerned with all of the eleven credibility assessment stages not just model validation and programmed model verification.

Browsing by Author "Balci, Osman"

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