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Showing papers in "ACM Computing Surveys in 1999"


Journal ArticleDOI
TL;DR: An overview of pattern clustering methods from a statistical pattern recognition perspective is presented, with a goal of providing useful advice and references to fundamental concepts accessible to the broad community of clustering practitioners.
Abstract: Clustering is the unsupervised classification of patterns (observations, data items, or feature vectors) into groups (clusters). The clustering problem has been addressed in many contexts and by researchers in many disciplines; this reflects its broad appeal and usefulness as one of the steps in exploratory data analysis. However, clustering is a difficult problem combinatorially, and differences in assumptions and contexts in different communities has made the transfer of useful generic concepts and methodologies slow to occur. This paper presents an overview of pattern clustering methods from a statistical pattern recognition perspective, with a goal of providing useful advice and references to fundamental concepts accessible to the broad community of clustering practitioners. We present a taxonomy of clustering techniques, and identify cross-cutting themes and recent advances. We also describe some important applications of clustering algorithms such as image segmentation, object recognition, and information retrieval.

14,054 citations


Journal ArticleDOI
TL;DR: A taxonomy that classifies 27 scheduling algorithms and their functionalities into different categories is proposed, with each algorithm explained through an easy-to-understand description followed by an illustrative example to demonstrate its operation.
Abstract: Static scheduling of a program represented by a directed task graph on a multiprocessor system to minimize the program completion time is a well-known problem in parallel processing. Since finding an optimal schedule is an NP-complete problem in general, researchers have resorted to devising efficient heuristics. A plethora of heuristics have been proposed based on a wide spectrum of techniques, including branch-and-bound, integer-programming, searching, graph-theory, randomization, genetic algorithms, and evolutionary methods. The objective of this survey is to describe various scheduling algorithms and their functionalities in a contrasting fashion as well as examine their relative merits in terms of performance and time-complexity. Since these algorithms are based on diverse assumptions, they differ in their functionalities, and hence are difficult to describe in a unified context. We propose a taxonomy that classifies these algorithms into different categories. We consider 27 scheduling algorithms, with each algorithm explained through an easy-to-understand description followed by an illustrative example to demonstrate its operation. We also outline some of the novel and promising optimization approaches and current research trends in the area. Finally, we give an overview of the software tools that provide scheduling/mapping functionalities.

1,373 citations


Journal ArticleDOI
TL;DR: The fundamental characteristics of active database systems are presented, a collection of representative systems within a common framework are described, the consequences for implementations of certain design decisions are considered, and tools for developing active applications are discussed.
Abstract: Active database systems support mechanisms that enable them to respond automatically to events that are taking place either inside or outside the database system itself. Considerable effort has been directed towards improving understanding of such systems in recent years, and many different proposals have been made and applications suggested. This high level of activity has not yielded a single agreed-upon standard approach to the integration of active functionality with conventional database systems, but has led to improved understanding of active behavior description languages, execution models, and architectures. This survey presents the fundamental characteristics of active database systems, describes a collection of representative systems within a common framework, considers the consequences for implementations of certain design decisions, and discusses tools for developing active applications.

561 citations


Journal ArticleDOI
TL;DR: This survey provides a comprehensive analysis of new paradigms and enabler concepts for mobile client-server computing, including mobile-aware adaptation, extended client- server model, and mobile data access.
Abstract: Recent advances in wireless data networking and portable information appliances have engendered a new paradigm of computing, called mobile computing, in which users carrying portable devices have access to data and information services regardless of their physical location or movement behavior. In the meantime, research addressing information access in mobile environments has proliferated. In this survey, we provide a concrete framework and categorization of the various ways of supporting mobile client-server computing for information access. We examine characteristics of mobility that distinguish mobile client-server computing from its traditional counterpart. We provide a comprehensive analysis of new paradigms and enabler concepts for mobile client-server computing, including mobile-aware adaptation, extended client-server model, and mobile data access. A comparative and detailed review of major research prototypes for mobile information access is also presented.

530 citations


Journal ArticleDOI
Jon Kleinberg1
TL;DR: The Web has become the most visible manifestation of a new medium: a global, populist hypertext, where researchers now release their results to the Web before they appear in print, and corporations list their URLs alongside their toll-free numbers.
Abstract: This has been a computer scientist's revolution; but we all share in its results. Only a few years ago, the World Wide Web was known just to a small research community; it is hard to remember that the voluminous content we see on the WWW, expanding by an estimated million pages each day, has grown up around us in so short a time. Researchers now release their results to the Web before they appear in print; corporations list their URLs alongside their toll-free numbers; news media and entertainment companies vie for the attention of a browsing audience. The Web has become the most visible manifestation of a new medium: a global, populist hypertext.

442 citations


Journal ArticleDOI
TL;DR: This paper investigates the current situation of Web development tools, both in the commercial and research fields, by identifying and characterizing different categories of solutions, evaluating their adequacy to the requirements of Web application development, enlightening open problems, and exposing possible future trends.
Abstract: The exponential growth and capillar diffusion of the Web are nurturing a novel generation of applications, characterized by a direct business-to-customer relationship. The development of such applications is a hybrid between traditional IS development and Hypermedia authoring, and challenges the existing tools and approaches for software production. This paper investigates the current situation of Web development tools, both in the commercial and research fields, by identifying and characterizing different categories of solutions, evaluating their adequacy to the requirements of Web application development, enlightening open problems, and exposing possible future trends.

397 citations


Journal ArticleDOI
TL;DR: This paper compares different indexing techniques proposed for supporting efficient access to temporal data based on a collection of important performance criteria, including the space consumed, update processing, and query time for representative queries.
Abstract: This paper compares different indexing techniques proposed for supporting efficient access to temporal data. The comparison is based on a collection of important performance criteria, including the space consumed, update processing, and query time for representative queries. The comparison is based on worst-case analysis, hence no assumptions on data distribution or query frequencies are made. When a number of methods have the same asymptotic worst-case behavior, features in the methods that affect average case behavior are discussed. Additional criteria examined are the pagination of an index, the ability to cluster related data together, and the ability to efficiently separate old from current data (so that larger archival storage media such as write-once optical disks can be used). The purpose of the paper is to identify the difficult problems in accessing temporal data and describe how the different methods aim to solve them. A general lower bound for answering basic temporal queries is also introduced.

364 citations


Journal ArticleDOI
TL;DR: This paper uses a formal approach to define important terms like fault, fault tolerance, and redundancy, which leads to four distinct forms of fault tolerance and to two main phases in achieving them: detection and correction.
Abstract: Fault tolerance in distributed computing is a wide area with a significant body of literature that is vastly diverse in methodology and terminology. This paper aims at structuring the area and thus guiding readers into this interesting field. We use a formal approach to define important terms like fault, fault tolerance, and redundancy. This leads to four distinct forms of fault tolerance and to two main phases in achieving them: detection and correction. We show that this can help to reveal inherently fundamental structures that contribute to understanding and unifying methods and terminology. By doing this, we survey many existing methodologies and discuss their relations. The underlying system model is the close-to-reality asynchronous message-passing model of distributed computing.

345 citations


Journal ArticleDOI
TL;DR: A framework for adaptive hypermedia systems (AHS) is introduced and some popular methods and techniques for adaptation are described, to illustrate the potential benefits of using adaptation in hypermedia applications.
Abstract: The navigational freedom in conventional hypermedia applications leads to comprehension and orientation problems (Nielsen 1990). Adaptive hypermedia attempts to overcome these problems by adapting the presentation of information and the overall link structure, based on a user model. This paper introduces a framework for adaptive hypermedia systems (AHS). It briefly describes some popular methods and techniques for adaptation. Examples and evaluations of existing AHS are used to illustrate the potential benefits of using adaptation in hypermedia applications.

318 citations


Journal ArticleDOI
TL;DR: Xanadu has always been much more ambitious, proposing an entire form of literature where links do not break as versions change, and in which there is a valid copyright system for frictionless, non-negotiated quotation at any time and in any amount.
Abstract: It has always been much more ambitious, proposing an entire form of literature where links do not break as versions change; where documents may be closely compared side by side and closely annotated; where it is possible to see the origins of every quotation; and in which there is a valid copyright system -a literary, legal and business arrangement -for frictionless, non-negotiated quotation at any time and in any amount. The Web trivialized this original Xanadu model, vastly but incorrectly simplifying these problems to a world of fragile ever-breaking oneway links, with no recognition of change or copyright, and no support for multiple versions or principled re-use. Fonts and glitz, rather than content connective structure, prevail.

151 citations


Journal ArticleDOI
TL;DR: This paper presents a tutorial on transport layer concepts and terminology, and a survey of transport layer services and protocols, and compared and contrasted with nineteen other protocols designed over the past two decades.
Abstract: Transport layer protocols provide for end-to-end communication between two or more hosts. This paper presents a tutorial on transport layer concepts and terminology, and a survey of transport layer services and protocols. The transport layer protocol TCP is used as a reference point, and compared and contrasted with nineteen other protocols designed over the past two decades. The service and protocol features of twelve of the most important protocols are summarized in both text and tables.

Journal ArticleDOI
TL;DR: This paper provides a tutorial-style introduction to some important approaches of Default Logic, based on operational models for these approaches, thus making them easily accessible to a broader audience, and more easily usable in practical applications.
Abstract: Default logic is one of the most prominent approaches to nonmonotonic reasoning, and allows one to make plausible conjectures when faced with incomplete information about the problem at hand. Default rules prevail in many application domains such as medical and legal reasoning.Several variants have been developed over the past year, either to overcome some perceived deficiencies of the original presentation, or to realize somewhat different intuitions. This paper provides a tutorial-style introduction to some important approaches of Default Logic. The presentation is based on operational models for these approaches, thus making them easily accessible to a broader audience, and more easily usable in practical applications.

Journal ArticleDOI
TL;DR: Algorithm Engineering is concerned with the design, analysis, implementation, tuning, debugging and experimental evaluation of computer programs for solving algorithmic problems.
Abstract: Algorithm Engineering is concerned with the design, analysis, implementation, tuning, debugging and experimental evaluation of computer programs for solving algorithmic problems. It provides methodologies and tools for developing and engineering efficient algorithmic codes and aims at integrating and reinforcing traditional theoretical approaches for the design and analysis of algorithms and data structures.


Journal ArticleDOI
TL;DR: Over the past twelve years, online algorithms have received considerable research interest and the term competitive analysis was coined when Sleator and Tarjan suggested comparing an online algorithm to an optimal offline algorithm.
Abstract: Over the past twelve years, online algorithms have received considerable research interest. Online problems had been investigated already in the seventies and early eighties but an extensive, systematic study started only when Sleator and Tarjan [41] suggested comparing an online algorithm to an optimal offline algorithm and Karlin, Manasse, Rudolph and Sleator [29] coined the term competitive analysis.

Journal ArticleDOI
TL;DR: Systems in which the user's main interaction with the hypertext was through a network map rather than a document viewer, such as gIBIS and Aquanet, presented a visual network containing typed links and nodes where the types are visually distinguished within the map.
Abstract: Hypertext began as a vision of interconnected reference materials [Bush 1945] and literature [Robertson 1998]. These early visions were joined by working systems that supported link-based navigation among documents as well as branching points within (hyper)documents [Engelbart 1984]. As the use of hypertext systems became more widespread, researchers realized that readers could become confused or lost as they navigated large networks [Conklin 1987a]. Systems such as NoteCards [Halasz 1987] addressed this problem by displaying maps of the hypertext's network structure. The success of NoteCards's "browser cards" and other hypertext maps gave rise to systems in which the user's main interaction with the hypertext was through a network map rather than a document viewer. For example, systems such as gIBIS [Conklin 1988] and Aquanet [Marshall 1991] presented a visual network containing typed links and nodes where the types are visually distinguished within the map; the network could be edited and manipulated through this presentation.

Journal ArticleDOI
TL;DR: In order to access any kind of stored information, one may store it at a specific location, and in the case of electronic information this could be a file name or a Web address, and thus these two areas of hypertext and information retrieval are tightly related.
Abstract: In order to access any kind of stored information, one may store it at a specific location, and in the case of electronic information this could be a file name or a Web address. If the location is not known or the amount of information to be accessed is greater than the number of locations that can be remembered, then it is necessary to find the information based on its attributes, its content, or its relationships to other pieces of information whose location is known. In the first two cases, we search, as in information retrieval, while in the latter we navigate, as in hypertext and thus these two areas of hypertext and information retrieval are tightly related [Agosti 1996].

Journal ArticleDOI
TL;DR: The Web Consortium's XML Linking working group is developing specifications to enable more advanced hypertext functionality on the Web: in particular fine-grained anchors, external annotation, and bidirectional links.
Abstract: The Web Consortium's XML Linking working group is developing specifications to enable more advanced hypertext functionality on the Web: in particular fine-grained anchors, external annotation, and bidirectional links. This paper examines basic goals and approaches; describes HTML linking limitations XML Linking seeks to overcome; and surveys the Working Group's primary specifications: XPath, XPointer, and XLink. As of this writing, the last two, while well advanced, are not final recommendations, and so are subject to change. Consult the W3C Web site for the latest versions.

Journal ArticleDOI
Mengchi Liu1
TL;DR: This paper discussesuctive databases from four different aspects: complex values, object orientation, higher-orderness, and updates, and examines four typical languages that address the corresponding issues.
Abstract: Deductive databases result from the integration of relational database and logic programming techniques. However, significant problems remain inherent in this simple synthesis from the language point of view. In this paper, we discuss these problems from four different aspects: complex values, object orientation, higher-orderness, and updates. In each case, we examine four typical languages that address the corresponding issues.

Journal ArticleDOI
TL;DR: This paper reviews recent work in the area of three dimensional visualization of the Web that has attempted to depict it in the form of a recognizable space; in other words, as a navigable landscape that may be visibly populated by its users.
Abstract: Although large-scale public hypermedia structures such as the World Wide Web are popularly referred to as "cyberspace", the extent to which they constitute a space in the everyday sense of the word is questionable. This paper reviews recent work in the area of three dimensional (3D) visualization of the Web that has attempted to depict it in the form of a recognizable space; in other words, as a navigable landscape that may be visibly populated by its users. Our review begins by introducing a range of visualizations that address different aspects of using the Web. These include visualizations of Web structure, especially of links, that act as 3D maps; browsing history; searches; evolution of the Web; and the presence and activities of multiple users. We then summarize the different techniques that are employed by these visualizations. We conclude with a discussion of key challenges for the future.

Journal ArticleDOI
TL;DR: The causes of hypertext link integrity problems are reflected on and techniques that may be used to maintain link integrity are reviewed.
Abstract: Hypertext links are connections between documents or parts of documents Generally the ends of links are represented by some kind of a reference to a document or part of a document When documents are moved or changed these references may cease to resolve to the correct places This paper reflects on the causes of this problem and reviews techniques that may be used to maintain link integrity Categories and Subject Descriptors: H54 (Information Interfaces and Presentation): Hypertext/Hypermedia - Architectures

Journal ArticleDOI
Ivan Marsic1
TL;DR: This paper presents a framework for sharing JavaBeans applications in real-time synchronous collaboration and research on knowledge-based quality-of-service management and multimodel human/machine interface is described.
Abstract: This paper presents a framework for sharing JavaBeans applications in real-time synchronous collaboration. A generic collaboration bus provides a plug-and-play environment that enables collaboration with applications that may or may not be collaboration aware. Research on knowledge-based quality-of-service management and multimodel human/machine interface is described.

Journal ArticleDOI
TL;DR: The Evaluation Working Group in the Defense Advanced Research Projects Agency (DARPA) Intelligent Collaboration and Visualization (IC&V) program has developed a methodology for evaluating collaborative systems, which consists of a framework for classification of CSCW systems, metrics and measures related to the various components in the framework, and a scenario-based evaluation approach.
Abstract: The Evaluation Working Group (EWG) in the Defense Advanced Research Projects Agency (DARPA) Intelligent Collaboration and Visualization (IC&V) program has developed a methodology for evaluating collaborative systems. This methodology consists of a framework for classification of CSCW (Computer Supported Cooperative Work) systems, metrics and measures related to the various components in the framework, and a scenario-based evaluation approach. This paper describes the components of this methodology. Two case studies of evaluations based on this methodology are also described.


Journal ArticleDOI
TL;DR: A software system consisting of a meeting recorder and browser was designed and developed to provide a higher level view of collaborative meetings, co-locational or distributed and a way to browse through and listen to those parts which are most relevant to the user.
Abstract: : The objective of this effort is to integrate and enhance existing technologies in speech recognition, speaker identification, and topic classification to provide cost-effective transcription, structural summarization, and retrieval of user-specified aspects of meetings. A software system consisting of a meeting recorder and browser was designed and developed to provide a higher level view of collaborative meetings, co-locational or distributed and a way to browse through and listen to those parts which are most relevant to the user.

Journal ArticleDOI
TL;DR: A large variety of computing systems, such as compilers, interpreters, static analyzers, and theorem provers, need to manipulate syntactic objects like programs, types, formulas, and proofs that contain variable binders,such as quantifiers, scoping operators, and parameters.
Abstract: A large variety of computing systems, such as compilers, interpreters, static analyzers, and theorem provers, need to manipulate syntactic objects like programs, types, formulas, and proofs. A common characteristic of these syntactic objects is that they contain variable binders, such as quantifiers, scoping operators, and parameters. The presence of binders complicates formal specifications and symbolic processing. Consider, for example, a function definition of the form

Journal ArticleDOI
TL;DR: The problems of ambiguity, context sensitivity, synonymy and polysemy that are inherent in natural languages, together with the abundance of web pages related to prominent topics, have exacerbated the difficulty of fulfilling the user’s information need.
Abstract: Classical information retrieval (IR) is concerned with indexing a collection of documents and answering queries by returning a ranked list of relevant documents [14, 21, 24]. With the growth of the web, the problems of ambiguity, context sensitivity, synonymy (two terms with the same meaning) and polysemy (one term with different meanings) that are inherent in natural languages, together with the abundance of web pages related to prominent topics, have exacerbated the difficulty of fulfilling the user’s information need. Most search sites have added directory-based topic browsing. The web is organized as a tree of topics, similar to the Dewey decimal system, the Library of Congress catalog, or the US Patent and Trademarks Office subject codes. Tree nodes are maintained by paid ontologists and/or specialist volunteers, such as at Yahoo!, The Mining Co., WWW Virtual Library, and Open Directory Project. This strategy may be biased because of sparsity of experts; at any rate it is biased away from the most accomplished and busiest people.

Journal ArticleDOI
TL;DR: How hypertext systems have evolved to become distributed and open providers of information services is described and the nature of the linking that forms the basis of hypertext functionality is examined.
Abstract: Hypertext, a neologism of the 1960s indicating something which is more than text, has taken over the attention of scholars, businesses and hobbyists in the form of the World Wide Web. Developed as a hypertext framework for information distribution [Berners-Lee 1992] , its overseeing organisation (W3C) has insisted on maintaining and developing a suite of open standards for data formats, communication protocols and programming interfaces to allow all comers to participate in a globally shared information repository. However the Web is just one example of how the development of hypertext philosophy, design and deployment has led to practical solutions for information dissemination, manipulation and maintenance. This paper describes how hypertext systems have evolved to become distributed and open providers of information services and examines the nature of the linking that forms the basis of hypertext functionality.

Journal ArticleDOI
TL;DR: The field of hypermedia has dealt with versioning issues for a long time, and newer systems, and an important protocol for the WWW, WebDAV, constitute modern approaches to the problem.
Abstract: Keeping multiple versions of the same electronic artifact is a necessity in many authoring fields, and a serious advantage in all of them. Hypermedia adds to that the issue of relationship management. This poses a few additional problems, especially conceptual ones, but it also provides a reliable and safe solution for the well-known problem of the referential integrity of links. The field of hypermedia has dealt with versioning issues for a long time, since Xanadu considered it a fundamental mechanism for its inner workings. Newer systems, and an important protocol for the WWW, WebDAV, constitute modern approaches to the problem.

Journal ArticleDOI
TL;DR: An overview of seventeen papers comprising a symposium on computer-supported cooperative work is provided, and five particular challenges for CSCW researchers are described, in the context of a military setting.
Abstract: Computer-supported cooperative work (CSCW) holds great importance and promise for modern society. This paper provides an overview of seventeen papers comprising a symposium on CSCW. The overview also discusses some relationships among the contributions made by each paper, and places those contributions into a larger context by identifying some of the key challenges faced by computer science reseachers who aim to help us work effectively as teams mediated through networks of computers. The paper also describes why the promise of CSCW holds particular salience for the U.S. military. In the context of a military setting, the paper describes five particular challenges for CSCW researchers. While most of these challenges might seem specific to military environments, many others probably already face similar challenges, or soon will, when attempting to collaborate through networks of computers. To support this claim, the paper includes a military scenario that might hit fairly close to home for many, and certainly for civilian emergency response personnel. After discussing the military needs for collaboration technology, the paper briefly outlines for motivation for a recent DARPA research program along these lines. That program, called Intelligent Collaboration and Visualization, sponsored the work reported in this symposium.