Distributed file systems have come into widespread use in recent years. Many allow files to be accessed over large geographic areas and across organizational boundaries. However, few systems to date have given much thought to how information should be organized in such a global environment. This paper describes the Prospero File System, a file system based on the Virtual System Model, a model for building large systems within which users construct their own virtual systems by selecting and organizing the objects and services of interest. This customized view of a globaJ file system makes it easier for users to keep track of files that they have identified as being of interest. The use of multiple name spaces can cause confusion. Such confusion is eliminated by support for closure: ever) ' object has an associated name space, and names specified by the object are resolved in that name space. Tools are provided to allow views to be kept up-to-date, and to allow views to be defined as functions of other (possibly changing) views. These tools promote sharing and enable the organization of files in ways that make it easier to identify information of interest than it is in existing systems. The prototype implementation has been used to organize information available from Internet archive sites; its directory service has been used from more than 7,500 systems in 29 countries. This paper discusses the goals of the Prospero File System, describes the prototype implementation, and discusses experience with the use of the system to date.

The dissertation presents the issues addressed in the design of Ficus, a large scale wide area distributed file system currently operational on a modest scale at UCLA. Key aspects of providing such a service include toleration of partial operation in virtually all areas; support for large scale, optimistic data replication; and a flexible, extensible modular design. Ficus incorporates a "stackable layers" modular architecture and full support for optimistic replication. Replication is provided by a pair of layers operating in concert above a traditional filing service. A "volume" abstraction and on-the-fly volume "grafting" mechanism are used to manage the large scale file name space. The replication service uses a f...

Naming is critical in distributed systems. Names identify files, services, processors, and users. A name service translates the names of objects to the information needed to access those objects. The growth of distributed systems brings with it an increase in the number of objects to be named. Existing naming techniques are derived from techniques used on centralized systems and are not sufficient for organizing the large number of objects that are becoming available. This dissertation presents the Virtual System Model, a new model for naming that helps users organize the information available in large systems. The Virtual System Model has four principal features: support for customizable name spaces, tools to help users construct name spaces, support for synonyms, and a m...

The role of workstations in future systems has been a hotly debated topic. Some believe the workstation is useful primarily as a terminal and that the computing of the future will be done on large multiprocessor systems. Others believe that workstations will be the processors of those multiprocessor systems. Still others believe that the role of the workstation will be between the two extremes, providing simple processing capabilities such as editing for the local user.

Introduction The Prospero file system is based on the Virtual System Model[1, 2, 3, 4]. It differs from traditional distributed file systems in several ways. In traditional file systems, the mapping of names to files is the same for all users. Prospero supports user centered naming: users construct their own view of the files that are accessible. The mapping from names to files is controlled by this view. Objects may be organized in multiple ways and the same object may may appear in different virtual systems, or even with multiple names in the same virtual system. Prospero provides several mechanisms to support customization. Among them are the union link and the filter. Directories can contain references to files and other directories that are stored on remote nodes. This allows distribution at a much finer level of granularity than is possible in traditional distributed file systems. 2 The Directory Mechanism In Prospero, the global file system consists of

At Healtheon, we used Tcl to rapidly develop a scalable, high performance rule engine for processing dynamic application logic. The nature of our application requirements, plus the challenge of delivering robust software in a timely manner made Tcl an optimal overall choice in our deployment. We were able to improve rule processing performance by careful language construction and support for concurrent execution. We developed a mechanism for implementing data-driven language extensions, called rule concepts, which allowed us to present a customized language for each client, and encouraged rule reusability. Our experience with using Tcl in our application system was also representative of software engineering choices that small companies often make in pursuit of rapidly developing a well-balanced system solution. 1