Georg Molter

World Wide Web caching: the application-level view of the Internet

The Internet has fallen prey to its most successful service, the World Wide Web. The networks do not keep up with the demands incurred by the huge amount of Web surfers. Thus, it takes longer and longer to obtain the information one wants to access via the World Wide Web. Many solutions to the problem of network congestion have been developed in distributed systems research in general and distributed file and database systems in particular. The introduction of caching and replication strategies has proven to help in many situations; therefore, these techniques are also applied to the Web. Although most problems and associated solutions are known, some circumstances are different with the Web, forcing the adaptation of known strategies. This article gives an overview of these differences and currently deployed, developed, and evaluated solutions.

Introducing application-level replication and naming into today's Web

Abstract Because of its enormous success, the World-Wide Web created many problems within the Internet, most of them due to its huge bandwidth requirements. Additional applications using the Webs infrastructure for distributed computing (see, e.g., [5]), even further increase network load. In this paper, we are presenting a comprehensive application-level approach to solving the Web-induced bandwidth and latency problems within the Internet while staying fully compatible with the current mechanisms of the World-Wide Web. Our approach is based on automated replication schemes and complementary name services. In this paper, we are going to introduce these two concepts, and explain the many advantages they bring not only to every Web user but also to the various network and service providers currently struggling to keep up with rising user demands. In addition to an abstract presentation of this approach, we are also highlighting the concepts of our freely available implementation.

Mapping requirements to reusable components using Design Spaces

A consistent implementation of component based reuse bears several implications for the design of the software development process. For instance, requirements engineering has to be tailored to particularly elicit information necessary for selecting and configuring appropriate components. Besides sketching our approach to component based system development, the paper shows how Design Spaces can be applied to actively support reuse oriented activities. Design Spaces allow us to uniformly describe requirements on and properties of software artefacts, as well as correlations between specific properties. As a consequence, they are well suited to guide the requirements capturing towards the properties of existing components, and to map those requirements to component selections and configurations. The paper demonstrates how to consistently deploy the Design Space technique throughout the process, leading to a complete and strongly tool-supported path from requirements capture to system implementation.

WebMake: integrating distributed software development in a structure-enhanced Web

Abstract In this paper, a technique for structuring large amounts of interdependent data is presented. This approach which facilitates graph-based hierarchical structuring and allows for the defintion of arbitrary views on graph structures can be applied to a broad range of very different application areas. Based on this concept we implemented a distributed software development environment supporting cooperative work on top of the World-Wide Web. In general, the approach is intended to serve as a basis for decentralized efforts to tame the immense and hardly manageable collection of data accessible in the Web.

Architecture-Centric Software Development Based on Extended Design Spaces

The realization of software projects can be significantly eased by extending the focus of reuse to architectural aspects instead of concentrating on separate software elements. Yet in any case, operational techniques are required to support the retrieval and selection of reusable items. To this end, we extend on the concept of design spaces which allows to describe the relevant properties of software elements in a semi-formal way. Moreover, we show how the concept of extended design spaces can be deployed in tools supporting component-and framework-based software development.

Booster: A WWW-based prototype of the global software highway

A framework for globally distributed software development and management environments, which we call Booster is presented. Additionally, the first experiences with WebMake, an application developed to serve as an experimental platform for a software development environment based on the World Wide Web and the Booster framework is introduced. Booster encompasses the basic building blocks and mechanisms necessary to support a truly cooperative distributed software development from the very beginning to the last steps in a software life cycle. It is thus a precursor of the Global Software Highway, in which providers and users can meet for the development, management, exchange and usage of all kind of software.<<ETX>>

Customization of system software for large-scale embedded applications1This work was funded by the DFG as part of the Sonderforschungsbereich SFB501, Development of Large Systems with generic Methods, Research project B5 (GENESYS) 1

Operating systems are one of the most frequently reused software components: almost every application is sitting on top of an OS which establishes the required runtime platform. It is claimed that bridging the gap between a high level application design and the OS is a costly process, especially in distributed systems. A conceptual framework is presented which aims at supporting the automatic generation of distributed runtime platforms from high-level application designs. It is based on the generic layout of operating system services, their extended description including nonfunctional properties, as well as analysis and development tools which filter out OS requirements from the application design.

Driving the composition of runtime platforms by architectural knowledge

Reusing app roved components is an a ttractive approach for the c ustomization o f runtime platforms in an economically sensible manner. However, the successful t ransition from particular requirements to a suitable architecture including appropriate components heavily relies on the expertise of t he system designers. In this paper, we propose an a rchitecture-driven approach to support runtime platform developers in the c omposition o f customized p latforms. Central to this approach is the explicit consideration of architectural aspects on an intermediate level of description. At this level, the appropriate matching o f requirements against properties of available components is controlled by formalized architectural knowledge. With SDL patterns and design spaces we present t wo techniques for performing this mapping process.

BSA: a framework for efficient accounting on wide-area networks

As global networks are being used by more and more people, they are becoming increasingly interesting for commercial applications. The success and change in direction of the World-Wide Web is a clear indication for this. However this success met a largely unprepared communications infrastructure. The Internet as an originally non-profit network did neither offer the security, nor the globally available accounting infrastructure by itself. These problems were addressed in the recent past, but in a seemingly ad-hoc manner. Several different accounting schemes sensible for only certain types of commercial transactions have been developed, which either seem to neglect the problems of scalability, or trade security for efficiency. Finally, some proposals aim at achieving near perfect security at the expense of efficiency, thus rendering those systems to be of no practical use. In contrast, this paper presents a suitably configurable scheme for accounting in a general, widely distributed client/server environment. When developing the protocol, special attention has been paid to make this approach work well in the future setting of high-bandwidth, high-latency internets. The developed protocol has been applied to a large-scale distributed application, a WWW-based software development environment.