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Knowledge and Data Engineering, IEEE Transactions on

Issue 4 • Date Jul/Aug 1999

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Displaying Results 1 - 12 of 12
  • Continual queries for Internet scale event-driven information delivery

    Page(s): 610 - 628
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    We introduce the concept of continual queries, describe the design of a distributed event-driven continual query system-OpenCQ, and outline the initial implementation of OpenCQ on top of the distributed interoperable information mediation system DIOM. Continual queries are standing queries that monitor update of interest and return results whenever the update reaches specified thresholds. In OpenCQ, users may specify to the system the information they would like to monitor (such as the events or the update thresholds they are interested in). Whenever the information of interest becomes available, the system immediately delivers it to the relevant users; otherwise, the system continually monitors the arrival of the desired information and pushes it to the relevant users as it meets the specified update thresholds. In contrast to conventional pull-based data management systems such as DBMSs and Web search engines, OpenCQ exhibits two important features: it provides push-enabled, event-driven, content-sensitive information delivery capabilities; and it combines pull and push services in a unified framework. By event-driven we mean that the update events of interest to be monitored are specified by users or applications. By content-sensitive, we mean the evaluation of the trigger condition happens only when a potentially interesting change occurs. By push-enabled, we mean the active delivery of query results or triggering of actions without user intervention View full abstract»

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  • Proxy cache algorithms: design, implementation, and performance

    Page(s): 549 - 562
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1132 KB)  

    Caching at proxy servers is one of the ways to reduce the response time perceived by World Wide Web users. Cache replacement algorithms play a central role in the response time reduction by selecting a subset of documents for caching, so that a given performance metric is maximized. At the same time, the cache must take extra steps to guarantee some form of consistency of the cached documents. Cache consistency algorithms enforce appropriate guarantees about the staleness of the cached documents. We describe a unified cache maintenance algorithm, LNC-R-WS-U, which integrates both cache replacement and consistency algorithms. The LNC-R-WS-U algorithm evicts documents from the cache based on the delay to fetch each document into the cache. Consequently, the documents that took a long time to fetch are preferentially kept in the cache. The LNC-R-W3-U algorithm also considers in the eviction consideration the validation rate of each document, as provided by the cache consistency component of LNC-R-WS-U. Consequently, documents that are infrequently updated and thus seldom require validations are preferentially retained in the cache. We describe the implementation of LNC-R-W3-U and its integration with the Apache 1.2.6 code base. Finally, we present a trace-driven experimental study of LNC-R-W3-U performance and its comparison with other previously published algorithms for cache maintenance View full abstract»

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  • An approach to mobile software robots for the WWW

    Page(s): 526 - 548
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2068 KB)  

    This paper describes a framework for developing mobile software robots by using the PLANET mobile object system, which is characterized by a language-neutral layered architecture, the native code execution of mobile objects, and asynchronous object passing. We propose an approach to implementing mobile Web search robots that takes full advantage of these characteristics, and we base our discussion of its effectiveness on experiments conducted in the Internet environment. The results show that the PLANET approach to mobile Web search robots significantly reduces the amount of data transferred via the Internet and that it enables the robots to work more efficiently than the robots in the conventional stationary scheme whenever nontrivial amounts of HTML files are processed View full abstract»

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  • Spatial join processing using corner transformation

    Page(s): 688 - 695
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    Spatial join finds pairs of spatial objects having a specific spatial relationship in spatial database systems. Since spatial join is a fairly expensive operation, we need an efficient algorithm taking advantage of the characteristics of available spatial access methods. In this paper, we propose a spatial join algorithm using corner transformation and show its excellence through experiments. To the extent of authors' knowledge, the spatial join processing using corner transformation is new. In corner transformation, two regions in one file joined with two adjacent regions in the other file share a large common area. The proposed algorithm utilizes this property in order to reduce the number of disk accesses for spatial join. Experimental results show that the performance of the algorithm is generally better than that of the R*-tree based algorithm proposed by Brinkhoff et al. (1993. 1994). This is a strong indication that corner transformation is a promising category of spatial access methods and that spatial operations can be performed better in the transform space than in the original space. This reverses the common belief that transformation will adversely effect the clustering. We also briefly mention that the join algorithm based on corner transformation has a nice property of being amenable to parallel processing. We believe that our result will provide a new insight towards transformation-based processing of spatial operations View full abstract»

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  • Volume leases for consistency in large-scale systems

    Page(s): 563 - 576
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    This article introduces volume leases as a mechanism for providing server-driven cache consistency for large-scale, geographically distributed networks. Volume leases retain the good performance, fault tolerance, and server scalability of the semantically weaker client-driven protocols that are now used on the Web. Volume leases are a variation of object leases, which were originally designed for distributed file systems. However, whereas traditional object leases amortize overheads over long lease periods, volume leases exploit spatial locality to amortize overheads across multiple objects in a volume. This approach allows systems to maintain good write performance even in the presence of failures. Using trace-driven simulation, we compare three volume lease algorithms against four existing cache consistency algorithms and show that our new algorithms provide strong consistency while maintaining scalability and fault-tolerance. For a trace-based workload of Web accesses, we find that volumes can reduce message traffic at servers by 40 percent compared to a standard lease algorithm, and that volumes can considerably reduce the peak load at servers when popular objects are modified View full abstract»

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  • MAgNET: mobile agents for networked electronic trading

    Page(s): 509 - 525
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1756 KB)  

    Electronic commerce technology offers the opportunity to integrate and optimize the global production and distribution supply chain. The computers of the various corporations, located throughout the world, will communicate with each other to determine the availability of components, to place and confirm orders, and to negotiate delivery timescales. We describe MAgNet, a system for networked electronic trading that is based on the Java mobile agent technology, called aglets. Aglets are dispatched by the buyer to the various suppliers, where they negotiate orders and deliveries, returning to the buyer with their best deals for approval. MAgNET handles the deep supply chain, where a supplier may need to contact further suppliers of subcomponents in order to respond to an enquiry. Experimental results demonstrate the feasibility of using the Java aglet technology for electronic commerce View full abstract»

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  • Managing complex documents over the WWW: a case study for XML

    Page(s): 629 - 638
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    The use of the World Wide Web as a communication medium for knowledge engineers and software designers is limited by the lack of tools for writing, sharing, and verifying documents written with design notations. For instance, the Z language has a rich set of mathematical characters, and requires graphic-rich boxes and schemas for structuring a specification document. It is difficult to integrate Z specifications and text on WWW pages written with HTML, and traditional tools are not suited for the task. On the other hand, a newly proposed standard for markup languages, namely XML, allows one to define any set of markup elements; hence, it is suitable for describing any kind of notation. Unfortunately, the proposed standard for rendering XML documents, namely XSL, provides for text-only (although sophisticated) rendering of XML documents, and thus it cannot be used for more complex notations. We present a Java-based tool for applying any notation to elements of XML documents. These XML documents can thus be shown on current-generation WWW browsers with Java capabilities. A complete package for displaying Z specifications has been implemented and integrated with standard text parts. Being a complete rendering engine, text parts and Z specifications can be freely intermixed, and all the standard features of XML (including HTML links and form elements) are available outside and inside Z specifications. Furthermore, the extensibility of our engine allows any additional notations to be supported and integrated with the ones we describe View full abstract»

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  • Enabling concept-based relevance feedback for information retrieval on the WWW

    Page(s): 595 - 609
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    The World Wide Web is a world of great richness, but finding information on the Web is also a great challenge. Keyword-based querying has been an immediate and efficient way to specify and retrieve related information that the user inquires. However, conventional document ranking based on an automatic assessment of document relevance to the query may not be the best approach when little information is given, as in most cases. In order to clarify the ambiguity of the short queries given by users, we propose the idea of concept-based relevance feedback for Web information retrieval. The idea is to have users give two to three times more feedback in the same amount of time that would be required to give feedback for conventional feedback mechanisms. Under this design principle, we apply clustering techniques to the initial search results to provide concept-based browsing. We show the performance of various feedback interface designs and compare their pros and cons. We measure precision and relative recall to show how clustering improves performance over conventional similarity ranking and, most importantly, we show how the assistance of concept-based presentation reduces browsing labor View full abstract»

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  • An alternative paradigm for scalable on-demand applications: evaluating and deploying the Interactive Multimedia Jukebox

    Page(s): 658 - 672
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    Straightforward, one-way delivery of audio/video through television sets has existed for many decades. In the 1980s, new services like pay-per-view and video-on-demand were touted as the “killer applications” for interactive TV. However, the hype quickly died away, leaving only hard technical problems and costly systems. As an alternative, we propose a new jukebox paradigm offering flexibility in how programs are requested and scheduled for playout. The jukebox scheduling paradigm offers flexibility ranging from complete viewer control (true video-on-demand), to complete service provider control (traditional broadcast TV). We first describe our proposed jukebox paradigm and relate it to other on-demand paradigms. We also describe several critical research issues, including the one-to-many delivery of content, program scheduling policies, server location, and the provision of advanced services like VCR-style interactivity and advanced reservations. In addition, we present our implementation of a jukebox-based service called the Interactive Multimedia Jukebox (IMJ). The IMJ provides scheduling via the World Wide Web (WWW) and content delivery via the Multicast Backbone (MBone). For the IMJ, we present usage statistics collected during the past couple of years. Furthermore, using this data and a simulation environment, we show that jukebox systems have the potential to scale to very large numbers of viewers View full abstract»

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  • JPernLite: extensible transaction services for the WWW

    Page(s): 639 - 657
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    Concurrency control is one of the key problems in design and implementation of collaborative systems such as hypertext/hypermedia systems, CAD/CAM systems, and software development environments. Most existing systems store data in specialized databases with built-in concurrency control policies, usually implemented via locking. It is desirable to construct such collaborative systems on top of the World Wide Web, but most Web servers do not support even conventional transactions, let alone distributed (multi-Website) transactions or flexible concurrency control mechanisms oriented toward team work-such as event notification, shared locks, and fine granularity locks. We present a transaction server that operates independently of Web servers or the collaborative systems, to fill the concurrency control gap. By default, the transaction server enforces the conventional atomic transaction model, where sets of operations are performed in an all-or-nothing fashion and isolated from concurrent users. The server can be tailored dynamically to apply more sophisticated concurrency control policies appropriate for collaboration. The transaction server also supports applications employing information resources other than Web servers, such as legacy databases, CORBA objects, and other hypermedia systems. Our implementation permits a wide range of system architecture styles View full abstract»

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  • Workflow and end-user quality of service issues in Web-based education

    Page(s): 673 - 687
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1072 KB)  

    The option of obtaining education over networks is quickly becoming a reality for all those who have access to the Internet and the World Wide Web (WWW). However, at present, network-based education (NBE) over the WWW and the Internet in general faces a number of pitfalls. The problems range from inadequate end-user quality of service (QoS), to inadequate materials, to shortcomings in learning paradigms, and to missing or inappropriate student assessment and feedback mechanisms. In this paper, we discuss some major issues that, although mostly solved for NBE, still face Web-based education (WEE). These include the required workflow-oriented technological and quality of service support. In discussing the issues, we use examples from a wide-area NBE/WBE system called NovaNET and a WEE system called Web Lecture System (WLS). We recommend that WEE system developers construct operational user (workflow) profiles before building their content and interfaces. Our experience is that, especially for synchronous WEE systems, user-level round-trip keystroke delays should not exceed about 250 ms and the overall availability of the system (including network-related service failures) should be at least 0.95. We also suggest that a successful WEE system will have a sound auto-adaptive knowledge assessment component, a “virtual” laboratory capability, and a set of strong collaborative functions View full abstract»

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  • WebCompanion: a friendly client-side Web prefetching agent

    Page(s): 577 - 594
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    Accessing remote sites of the World Wide Web is often a frustrating experience for users because of long Web page retrieval times even over relatively fast Internet connections. Users are more likely to embrace the further expansion of the role of the Web into a major infrastructure for electronic commerce and for information, application, and multimedia delivery if Web accesses can be accelerated. One technique that attempts this is prefetching. We built a client-side Java-implemented prefetching agent, WebCompanion, which employs a novel adaptive, fast, and selective online prefetching strategy based on estimated round-trip times for Web resources. This strategy efficiently hides the access latencies for slow resources while at the same time limiting the network and server overhead and local resource consumption to moderate levels. Our extensive experiments show an average access speedup of greater than 50 percent and an average network byte overhead of less than 150 percent using WebCompanion over a fast Internet connection. We measured a slight acceleration in accessing the Web through WebCompanion even in a pessimistic scenario where the user never requests a prefetched document View full abstract»

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Aims & Scope

IEEE Transactions on Knowledge and Data Engineering (TKDE) informs researchers, developers, managers, strategic planners, users, and others interested in state-of-the-art and state-of-the-practice activities in the knowledge and data engineering area.

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Meet Our Editors

Editor-in-Chief
Jian Pei
Simon Fraser University