The OSGi specification defines a Java-based service platform for dynamically deploying services into networked environments. OSGi technology originally targeted home services gateways, but is now used as a general Java application extensibility mechanism. The main abilities contributing to its growing influence are its support of a dynamic service deployment life cycle and its amenability to remote management. Microsoft's.NET platform, in some ways, improves upon the Java platform, but it still lacks explicit support for building dynamically extensible systems like those made possible by the OSGi framework for Java. This paper presents the results of an effort to create an OSGi-like service platform for the.NET platform. 1.

The open services gateway initiative (OSGi) defines and promotes open specifications for the delivery of managed services into networked environments. A key element of this initiative is the OSGi framework, which is a lightweight framework for deploying and executing service-oriented applications. This paper focuses on the OSGi framework by first discussing some implementation details of an open source implementation of the OSGi framework, called Oscar. The paper then presents issues that arose or whose importance was magnified through implementing and/or using the OSGi framework.

This paper describes a project, called Gravity, that defines a component model, where components provide and require services (i.e., functionality) and all component interaction occurs via services. This approach introduces service-oriented concepts into a component model and execution environment. The goal is to support the construction and execution of component-based applications that are capable of autonomously adapting at run time due to the dynamic availability of the services provided by constituent components. In this component model the execution environment manages an application that is described as an abstract composition that can adapt and evolve at run time depending on available functionality. The motivation of Gravity is to simplify the construction of applications where dynamic availability arises, ranging from modern extensible systems to novel computing approaches, such as context-aware applications.

This paper describes a project, called Gravity, that is providing support for building client-side applications out of dynamically available building blocks. The purpose behind this work is not only to deal with real-world issues already facing developers and end-users, but to also work toward a grander vision. In this vision, applications are built using context-aware architectures, meaning that context (e.g., location, environment, user task) is used as a filter to determine which building blocks are relevant to the application at any given time. The main concept underlying this vision is dynamically available building blocks, i.e., building blocks that can appear or disappear at any time. The Gravity technology described in this paper is a starting point for such research.

Configuring and deploying a large software system is complicated when the system is composed of components and when there are numerous possible configurations for the system. In such a scenario, it is difficult for end users to specify and install an appropriate configuration for their specific environment. Defining all valid configurations of a software system is challenging, and can be addressed through a concise specification that can generate all of the possible configurations. The Deployable Software Description (DSD) part of the University of Colorado Software Dock project, is one such specification format. But using the DSD runs the risk that the set of generated configurations includes some that are invalid with respect to constraints defined independently of the DSD. The paper describes a framework to support the analysis of DSD specifications to help developers detect potentially invalid configurations. This analysis assumes that the system components are annotated with properties, and an analysis tool is provided that takes a specific configuration and analyzes it for conflicts with respect to some set of constraints. Using the DSD, we can enumerate and analyze configurations to verify their validity. The results can be used to modify the DSD to avoid future generation of invalid configurations.

Software deployment is an evolving collection of interrelated processes such as release, install, adapt, reconfigure, update, activate, deactivate, remove, and retire. The connectivity of large networks, such as the Internet, is affecting how software deployment is being performed. To take full advantage of this connectivity, new software deployment technologies must be introduced in order to support these processes. The Software Dock research project is creating a distributed, agent-based deployment framework to support the ongoing cooperation and negotiation among software producers themselves and among software producers and software consumers. This deployment framework is enabled by the use of a standardized semantic schema for describing software systems, called the Deployable Software Description (DSD) format. The Software Dock employs agents to traverse between software producers and consumers and to perform software deployment activities by interpreting the semantic descriptions of the software systems. The Software Dock infrastructure enables software producers to offer high-level deployment services that were previously not possible to their customers.

Software distribution is evolving from a physical media approach to one where it is practical and advantageous to leverage the connectivity of networks. Network distribution of software systems provides timeliness and continuity of evolution not possible with physical media distribution methods. To support network-based software distribution, companies and organizations such as Microsoft, Marimba, and the Desktop Management Task Force (DMTF) are strengthening their efforts to package software systems in a way that is conducive to network distribution and management. The result of these efforts has led to the creation of software description languages and schema such as the Open Software Description format created by Microsoft and Marimba and the Management Information Format created by DMTF. While these efforts are steps in the right direction, they do not address deployment issues in a complete and systematic fashion. The contribution of this paper is to evaluate these leading software description technologies.

Few tools exist to address the post-development activities of configuring, releasing, installing, updating, reconfiguring, and even de-installing a software system. Certainly there is no unified approach for all of these activities, and none that can take full advantage of a wide-area network. The Software Dock represents an architecture for supporting post-development activities in such a setting. It is designed as a system of loosely-coupled, cooperating, distributed components that are bound together by a wide-area messaging and event system. In this paper we describe the Software Dock architecture and discuss the use of a prototype in deploying a complex system.

This paper presents evidence that several, judiciously placed file caches could reduce the volume of FTP traffic by 42%, and hence the volume of all NSFNET backbone traffic by 21%. In addition, if FTP client and server software automatically compressed data, this savings could increase to 27%. We believe that a hierarchical architecture of whole file caches, modeled after the existing name server's caching architecture, could become a valuable part of any internet.We derived these conclusions by performing trace driven simulations of various file caching architectures, cache sizes, and replacement policies. We collected the traces of file transfer traffic employed in our simulations on a network that connects the NSFNET backbone to a large, regional network. This particular regional network is responsible for about 5 to 7% of NSFNET traffic.While this paper's analysis and discussion focus on caching for FTP file transfer, the proposed caching architecture applies to caching objects from other internetwork services.