Computing devices and applications are now used beyond the desktop, in diverse environments, and this trend toward ubiquitous computing is accelerating. One challenge that remains in this emerging research field is the ability to enhance the behavior of any application by informing it of the context of its use. By context, we refer to any information that characterizes a situation related to the interaction between humans, applications and the surrounding environment. Context-aware applications promise richer and easier interaction, but the current state of research in this field is still far removed from that vision. This is due to three main problems: (1) the notion of context is still ill defined; (2) there is a lack of conceptual models and methods to help drive the design of context-aware applications; and (3) no tools are available to jump-start the development of context-aware applications. In this paper, we address these three problems in turn. We first define context, identify categories of contextual information, and characterize context-aware application behavior. Though the full impact of context-aware computing requires understanding very subtle and high-level notions of context, we are focusing our efforts on the pieces of context that can be inferred automatically from sensors in a physical environment. We then present a conceptual framework that separates the acquisition and representation of context from the delivery and reaction to context by a contextaware application. We have built a toolkit, the Context Toolkit, that instantiates this conceptual framework and supports the rapid development of a rich space of context-aware applications. We illustrate the usefulness of the conceptual framework by describing a number of contextaware applications that h...

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Rapid growth in data volume, user base, and data diversity render Internet-accessible information increasingly difficult to use effectively. In this paper we introduce Harvest, a system that provides an integrated set of customizable tools for gathering information from diverse repositories, building topic-specific content indexes, flexibly searching the indexes, widely replicating them, and caching objects as they are retrieved across the Internet. The system interoperates with WWW clients and with HTTP,FTP, Gopher, and NetNews information resources. We discuss the design and implementation of Harvest and its subsystems, give examples of its uses, and provide measurements indicating that Harvest can significantly reduce server load, network traffic, and space requirements when building indexes, compared with previous systems. We also discuss several popular indexes wehave built using Harvest, underscoring the customizability and scalability of the system.

Over the past several years, a number of information discovery and access tools have been introduced in the Internet, including Archie, Gopher, Netfind, and WAIS. These tools have become quite popular, and are helping to redefine how people think about wide-area network applications. Yet, they are not well suited to supporting the future information infrastructure, which will be characterized by enormous data volume, rapid growth in the user base, and burgeoning data diversity. In this paper we indicate trends in these three dimensions and survey problems these trends will create for current approaches. We then suggest several promising directions of future resource discovery research, along with some initial results from projects carried out by members of the Internet Research Task Force Research Group on Resource Discovery and Directory Service.

A fundamental problem with the World Wide Web is the enormous number of resources available and the difficulty of locating and tracking everything. In this paper we will discuss two tools, GENVL and WWWW, designed to deal in different ways with resource location on the WWW. GENVL is an interactive user-driven hierarchical virtual library system for cataloguing Web resources. The real power of GENVL comes from the built-in recursion which is the key to extendibility and to avoiding the generation of massive linear lists. GENVL has been accessed 112,000 times in 4 months. WWWW - the WWW Worm - is a resource location tool. It is intended to locate almost all of the WWW-addressable resources on the Internet, and provide a powerful search interface to those resources. Searches can be performed on document titles, reference hypertext, or within the components of the URL name strings of documents - for example to locate all mpeg movies in Finland. WWWW has been accessed 60,000 times in 45 day...

The paper summarizes the essential properties of document retrieval and reviews both conventional practice and research findings, the latter suggesting that simple statistical techniques can be effective. It then considers the new opportunities and challenges presented by the ability to search full text directly (rather than e.g. titles and abstracts), and suggests appropriate approaches to doing this, with a focus on the role of natural language processing. The paper also comments on possible connections with data and knowledge retrieval, and concludes by emphasizing the importance of rigorous performance testing. This paper will appear in Communications of the ACM. 2 Introduction Automatic text, or document, retrieval has recently become a topic of interest for those working in natural language processing (NLP). The aim of this article is to indicate the key properties of document retrieval, distinguishing it from both data retrieval and question answering; to summarize past exper...

This paper presents an overview of resource discovery services currently available on the Internet. First, we survey a number of existing Internet discovery services. Then, we present a taxonomy of design decisions and characteristics of tools for the Internet resource discovery problem [30]. The Wide Area Information Server

Practical information retrieval systems must manage large volumes of data, often divided into several collections that may be held on separate machines. Techniques for locating matches to queries must therefore consider identification of probable collections as well as identification of documents that are probable answers. Furthermore, the large amounts of data involved motivates the use of compression, but in a dynamic environment compression is problematic, because as new text is added the compression model slowly becomes inappropriate. In this paper we describe solutions to both of these problems. We show that use of centralised blocked indexes can reduce overall query processing costs in a multi-collection environment, and that careful application of text compression techniques allow collections to grow by several orders of magnitude without recompression becoming necessary. 1 Introduction Practical information systems are required to store many gigabytes of data while supporting ...

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Multicasting is a technique that enables a single packet transmission to reach one or more destinations or group. The primary benefits of a packet reaching multiple destinations from a single transmission are threefold: bandwidth minimization; the exploitation of parallelism in the network; the optimization of transmitter costs. In this thesis we investigate and analyse each of the different network layer multicast algorithms and protocols, looking in particular at their scalability, since multicast scalability was the primary motivator for this work. Our first and most significant contribution involves the presentation of a new multicast architecture and protocol, designed for best-effort, connectionless datagram networks such as the IP Internet. This new architecture typically offers considerably more favourable scaling characteristics than do existing multicast schemes. Our other most significant contribution is the security architecture that is integral in our new multicast proposa...