We identify crucial design issues in building a distributed inverted index for a large collection of Web pages. We introduce a novel pipelining technique for structuring the core index-building system that substantially reduces the index construction time. We also propose a storage scheme for creating and managing inverted files using an embedded database system. We suggest and compare different strategies for collecting global statistics from distributed inverted indexes. Finally, we present performance results from experiments on a testbed distributed Web indexing system that we have implemented.

Crash-only programs crash safely and recover quickly. There is only one way to stop such software---by crashing it---and only one way to bring it up---by initiating recovery. Crash-only systems are built from crash-only components, and the use of transparent component-level retries hides intra-system component crashes from end users. In this paper we advocate a crash-only design for Internet systems, showing that it can lead to more reliable, predictable code and faster, more effective recovery. We present ideas on how to build such crash-only Internet services, taking successful techniques to their logical extreme.

Pervasive computing provides an attractive vision for the future of computing. Computational power will be available everywhere. Mobile and stationary devices will dynamically connect and coordinate to seamlessly help users in accomplishing their tasks. However, for this vision to become a reality, developers must build applications that constantly adapt to a highly dynamic computing environment. To make the developers' task feasible, we introduce a system architecture for pervasive computing, called one.world . Our architecture provides an integrated and comprehensive framework for building pervasive applications. It includes a set of services, such as service discovery, checkpointing, migration, and replication, that help to structure applications and directly simplify the task of coping with constant change. We describe the design and implementation of our architecture and present the results of an evaluation, which includes two case studies.

Proportional-share resource management is becoming increasingly important in today's computing environments. In particular, the growing use of the computational resources of central service providers argues for a proportional-share approach that allows resource principals to obtain allocations that reflect their relative importance. In such environments, resource principals must be isolated from one another to prevent the activities of one principal from impinging on the resource rights of others. However, such isolation limits the flexibility with which resource allocations can be modified to reflect the actual needs of applications. We present extensions to the lottery-scheduling resource management framework that increase its flexibility while preserving its ability to provide secure isolation. To demonstrate how this extended framework safely overcomes the limits imposed by existing proportional-share schemes, we have implemented a prototype system that uses the framework to manage...

Even after decades of software engineering research, complex computer systems still fail. This paper makes the case for increasing research emphasis on dependability and, specifically, on improving availability by reducing time-to-recover. All software fails at some point, so systems must be able to recover from failures. Recovery itself can fail too, so systems must know how to intelligently retry their recovery. We present here a recursive approach, in which a minimal subset of components is recovered first

Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) Program Office plays a key part in helping NASA maintain this important role. The NASA STI Program Office is operated by Langley Research Center, the lead center for NASA's scientific and technical information. The NASA STI Program Office provides access to the NASA STI Database, the largest collection of aeronautical and space science STI in the world. The Program Office is also NASA's institutional mechanism for disseminating the results of its research and development activities. These results are published by NASA in the NASA STI Report Series, which includes the following report types:

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Most current information management systems can be classified into text retrieval systems, relational/object database systems, or semistructured/XML database systems. However, in practice, many applications data sets involve a combination of free text, structured data, and semistructured data. Hence, integration of different types of information management systems has been, and continues to be, an active research topic. In this paper, we present a short survey of prior work on integrating and inter-operating between text, structured, and semistructured database systems. We classify existing literature based on the kinds of systems being integrated and the approach to integration. Based on this classification, we identify the challenges and the key themes underlying existing work in this area.

In temporal document databases and temporal XML databases, temporal text-containment queries are a potential performance bottleneck. In this paper we describe how to manage documents and index structures in such databases in a way that makes temporal textcontainment querying feasible. We describe and discuss different index structures that can improve such queries. Three of the alternatives have been implemented in the V2 temporal document database system, and the performance of the index structures is studied using temporal web data. The results show that even a very simple time-indexing approach can reduce query cost by up to three orders of magnitude.

The demand for bandwidth in computer networks has been growing at a steady pace for the last several years, and a significant portion of that traffic is for the World Wide Web. At the same time, a large fraction of Internet users continue to rely on slow "last mile" links, such as modems and wireless links. We present xProxy, a transparent proxy system that uses deltas and compression to increase the performance of web traffic over slow links. By using compression, the average modem transfer time for HTML pages can be reduced by a factor of 2.6, while the use of compressed deltas can reduce the transfer time by a factor of 6.2. Also, xProxy was used by four people over 10 days, and provided total "real" bandwidth savings of 53.2%. The techniques used by our system, if utilized by other proxies and/or web servers, could also reduce the amount of web traffic that traverses any network.