Using real options to select stable Middleware-induced software architectures

The requirements that force decisions towards building distributed system architectures are usually of a non-functional nature. Scalability, openness, heterogeneity, and fault-tolerance are examples of such non-functional requirements. The current trend is to build distributed systems with middleware, which provide the application developer with primitives for managing the complexity of distribution, system resources, and for realising many of the non-functional requirements. As non-functional requirements evolve, the `coupling' between the middleware and architecture becomes the focal point for understanding the stability of the distributed software system architecture in the face of change. It is hypothesised that the choice of a stable distributed software architecture depends on the choice of the underlying middleware and its flexibility in responding to future changes in non-functional requirements. Drawing on a case study that adequately represents a medium-size component-based distributed architecture, it is reported how a likely future change in scalability could impact the architectural structure of two versions, each induced with a distinct middleware: one with CORBA and the other with J2EE. An option-based model is derived to value the flexibility of the induced-architectures and to guide the selection. The hypothesis is verified to be true for the given change. The paper concludes with some observations that could stimulate future research in the area of relating requirements to software architectures

Finite state machine based SDL

No abstract available

Security in a Distributed Processing Environment

Distribution plays a key role in telecommunication and computing systems today. It has become a necessity as a result of deregulation and anti-trust legislation, which has forced businesses to move from centralised, monolithic systems to distributed systems with the separation of applications and provisioning technologies, such as the service and transportation layers in the Internet. The need for reliability and recovery requires systems to use replication and secondary backup systems such as those used in ecommerce. There are consequences to distribution. It results in systems being implemented in heterogeneous environment; it requires systems to be scalable; it results in some loss of control and so this contributes to the increased security issues that result from distribution. Each of these issues has to be dealt with. A distributed processing environment (DPE) is middleware that allows heterogeneous environments to operate in a homogeneous manner. Scalability can be addressed by using object-oriented technology to distribute functionality. Security is more difficult to address because it requires the creation of a distributed trusted environment. The problem with security in a DPE currently is that it is treated as an adjunct service, i.e. and after-thought that is the last thing added to the system. As a result, it is not pervasive and therefore is unable to fully support the other DPE services. DPE security needs to provide the five basic security services, authentication, access control, integrity, confidentiality and non-repudiation, in a distributed environment, while ensuring simple and usable administration. The research, detailed in this thesis, starts by highlighting the inadequacies of the existing DPE and its services. It argues that a new management structure was introduced that provides greater flexibility and configurability, while promoting mechanism and service independence. A new secure interoperability framework was introduced which provides the ability to negotiate common mechanism and service level configurations. New facilities were added to the non-repudiation and audit services. The research has shown that all services should be security-aware, and therefore would able to interact with the Enhanced Security Service in order to provide a more secure environment within a DPE. As a proof of concept, the Trader service was selected. Its security limitations were examined, new security behaviour policies proposed and it was then implemented as a Security-aware Trader, which could counteract the existing security limitations.IONA TECHNOLOGIES PLC & ORANG

Designing Distributed, Component-Based Systems for Industrial Robotic Applications

none3noneM. Amoretti; S. Caselli; M. ReggianiM., Amoretti; S., Caselli; Reggiani, Monic

A performance measurement tool for the resource access decider authorization service prototype

The RAD (Resource Access Decider) authorization service is implemented at CADSE (Center for Advanced Distributed Systems Engineering) as a prototype based on the OMG (Object Management Group) CORBA (Common Object Reference Broker Architecture) specification for RAD (Resource Access Decider) facility. It is a part of the research towards developing performance efficient and available distributed authorization service. In order to test the performance of such an implementation, measurements have to be made to obtain data, which can be used to analyze the resource consumption and system behavior under different configurations. Such tests will have to be performed throughout the development process and this requires automating the performance measurement process to streamline the different stages of data gathering, analysis and interpretation. This thesis presents a performance measurement tool based on the DOVE (Distributed Object Visualization Environment) framework, capable of running the tests, gathering the data, computing and interpreting the data into graphical formats. The tool also provides a view of the system behavior by monitoring the performance of the individual components within the RAD prototype

Designing web-based adaptive learning environment : distils as an example

In this study, two components are developed for the Web-based adaptive learning: an online Intelligent Tutoring Tool (ITT) and an Adaptive Lecture Guidance (ALG). The ITT provides students timely problem-solving help in a dynamic Web environment. The ALG prevents students from being disoriented when a new domain is presented using Web technology. A prototype, Distributed Intelligent Learning System (DISTILS), has been implemented in a general chemistry laboratory domain. In DISTILS, students interact with the ITT through a Web browser. When a student selects a problem, the problem is formatted and displayed in the user interface for the student to solve. On the other side, the ITT begins to solve the problem simultaneously. The student can then request help from the ITT through the interface. The ITT interacts with the student, verifying those solution activities in an ascending order of the student knowledge status. In DISTILS, a Web page is associated with a HTML Learning Model (HLM) to describe its knowledge content. The ALG extracts the HLM, collects the status of students\u27 knowledge in HLM, and presents a knowledge map illustrating where the student is, how much proficiency he/she already has and where he/she is encouraged to explore. In this way, the ALG helps students to navigate the Web-based course material, protecting them from being disoriented and giving them guidance in need. Both the ITT and ALG components are developed under a generic Common Object Request Broker Architecture (CORBA)-driven framework. Under this framework, knowledge objects model domain expertise, a student modeler assesses student\u27s knowledge progress, an instruction engine includes two tutoring components, such as the ITT and the ALG, and the CORBA-compatible middleware serves as the communication infrastructure. The advantage of such a framework is that it promotes the development of modular and reusable intelligent educational objects. In DISTILS, a collection of knowledge objects were developed under CORBA to model general chemistry laboratory domain expertise. It was shown that these objects can be easily assembled in a plug-and-play manner to produce several exercises for different laboratory experiments. Given the platform independence of CORBA, tutoring objects developed under such a framework have the potential to be easily reused in different applications. Preliminary results showed that DISTILS effectively enhanced learning in Web environment. Three high school students and twenty-two NJIT students participated in the evaluation of DISTILS. In the final quiz of seven questions, the average correct answers of the students who studied in a Web environment with DISTILS (DISTILS Group) was 5.3, and the average correct answers of those who studied in the same Web environment without DISTILS (NoDISTILS Group) was 2.75. A t-test conducted on this small sample showed that the DISTILS group students significantly scored better than the NoDISTILS group students