Uffe Kock Wiil

The flag taxonomy of open hypermedia systems

This paper presents a taxonomy for open hypermedia systems. The purpose of the Flag taxonomy is manifold: (1) to provide a framework to classify and concisely describe individual systems, (2) to characterize what an open hypermedia system is, (3) to provide a framework for comparing di erent systems in a system independent way, and (4) to provide an overview of the design space of open hypermedia systems. The Flag taxonomy builds on the achievements of the Dexter model. It extends the terminology of the Dexter model to adequately cover issues that relate to open hypermedia systems such as integration and use of thirdparty applications to edit and display hypermedia components. Two of the most prominent open hypermedia systems, DeVise Hypermedia and Microcosm, are used as case studies. The Flag taxonomy is used to compare these systems on a carefully selected set of aspects that distinguish open hypermedia systems from other hypermedia systems.

Hyperform: using extensibility to develop dynamic, open, and distributed hypertext systems

An approach to flexible hyperbase (hypertext database) support predicated on the notion of extensibility is presented. The extensible hypertext platform (Hyperform) implements basic hyperbase services that can be tailored to provide specialized hyperbase support. Hyperform is based on an internal computational engine that provides an objectoriented extension language which allows new data model objects and operations to be added at runtime. Hyperform has a number of built-in classes to provide basic hyperbase features such as concurrency control, notification control (events), access control, version control and search and query. Each of these classes can be specialized using multiple inheritance to form virtually any type of hyperbase support needed in next generation hypertext systems. This approach greatly reduces the effort required to provide high quality customized hyperbase support for distributed hypertext applications. Hyperform is implemented and operational in Unix environments. This paper describes the Hyperform approach, discusses its advantages and disadvantages, and gives examples of simulating the HAM and the Danish HyperBase in Hyperform. Hyperform is compared with related work from the HAM generation of hyperbase systems and the current status of the project is reviewed.

The HyperDisco approach to open hypermedia systems

Computing support for large engineering enterprises provides an example of the need for hypermedia-based collaborative computing systems composed of a large number of distributed heterogeneous tools. These computing environments place complex requirements on the underlying hypermedia platform. To support integration of independently written tools for these environments, hypermedia platforms must address several important issues such as scalability, openness, distribution, heterogeneity, interoperability, extensibility and computation. This paper describes the HyperDisco approach to open hypermedia systems. HyperDisco provides an extensible object-oriented hypermedia platform supporting intertool linking, computation, concurrency control, noti cation control, version control, access control, query and search, and various other features. The present work has two main objectives: 1) to provide a platform to integrate existing and future distributed heterogeneous tools and data formats and 2) to provide a platform to extend integrated tools to handle multiple collaborating users and multiple versions of shared artifacts. The paper presents important dimensions of hypermedia platforms that helped to formulate the goals for HyperDisco, the HyperDisco prototype, and two integration examples to illustrate the distinctive features of the HyperDisco approach.

Addressing Interoperability in Open Hypermedia: the Design of the Open Hypermedia Protocol

Abstract Early hypertext systems were monolithic and closed, but newer systems tend to be open, distributed, and support collaboration. While this development has resulted in increased openness and flexibility, integration or adaptation of various different tools (such as content editors, viewers, services, or even other link servers) has remained a tedious task. Many developers were implementing essentially similar components, simply for the benefit of having their own platform on which to experiment with hypertexts. The open hypermedia community is addressing this issue of interoperability between open hypermedia systems. The goal of this effort is to provide an open framework that can be used by application developers outside the community to construct more powerful hypermedia-aware applications. The design and evolution of this framework is presented along with the requirements that drove its development. The framework has matured to the point where it has supported the creation of a number of researc...

Workspaces: the HyperDisco approach to Internet distribution

Hypermedia concepts are currently being deployed in a variety of information systems such as the World Wide Web, software development environments, large engineering enterprises, collaborative authoring systems, and digital library systems. The complex requirements of these application areas have resulted in extensive research into hypermedia infrastructures. The HyperDisco project is about design, development, deployment and assessment of hypermedia infrastructures. Previous HyperDisco experiments have dealt with integration of a small set of tools supporting authoring and extension of the integrated tools to support multiple collaborating users and multiple versions of shared files. These experiments were conducted on a local area network using a single centralized workspace. The latest version of HyperDisco supports collaboration and versioning over multiple workspaces distributed across the Internet. This paper gives a brief overview of HyperDisco, describes the workspace concept and reports on the latest experiments: (1) an experiment that allows the use of multiple workspaces on a local area network, (2) an experiment that allows workspaces to be distributed across the Internet, and (3) an experiment focusing on hypermedia modeling and presentation issues of distributed workspaces.

Multiple open services: a new approach to service provision in open hypermedia systems

Over the past decade, hypermedia systems have become increasingly open, distributed, and modular. As a direct result of this, open hypermedia systems have been increasingly successful in providing middleware services such as linking to a large set of clients. This paper presents a new approach to service provision in open hypermedia systems based on the concept of multiple open services. The overall idea with multiple open services is to rethink the way in which services are provided to clients. The goal is to split up services into components, each of which provides a general, scalable, and functionally independent (orthogonal) service. This results in a highly flexible architectural framework that can serve as a vehicle to further investigate many of the open issues relating to open hypermedia systems. The approach can be viewed as a natural next step in the evolution towards more open, distributed, and modular hypermedia systems. The concept of multiple open services is described in detail, and a proof of concept implementation called Construct is presented.

Evolving hypermedia middleware services: lessons and observations

In this paper, we consider the evolution of hypermedia system architectures from the monolithic systems of the 1980’s to the middleware-oriented component-based open systems of today. We look at the various problems that users and system designers encountered with systems at various stages of this development, focusing particularly on problems that were solved or caused by moving toward a more middleware-oriented approach. Although we cast our discussion in terms of specific hypermedia systems, we believe that many of our observations on the advantages and challenges of our current middleware approach may be helpful to those in other areas of system research.

Interoperability between hypermedia systems: the standardisation work of the OHSWG

CONTENTS OF THE TECHNICAL BRIEFING The Open Hypermedia Systems Working Group (OHSWG) was formed at the second workshop on open hypermedia systems (OHS), held in April, 1996, in Washington, DC, in conjunction with the 1996 ACM Conference on Hypertext. The original purpose of defining an open hypermedia protocol for OHS clients has evolved into an effort to standardise general hypermedia systems work. This broader effort is driven by the desire to maximise the applicability of the last decade of hypermedia systems and infrastructure research.

Hyperform: a hypermedia system development environment

Development of hypermedia systems is a complex matter. The current trend toward open, extensible, and distributed multiuser hypermedia systems adds additional complexity to the development process. As a means of reducing this complexity, there has been an increasing interest in hyperbase management systems that allow hypermedia system developers to abstract from the intricacies and complexity of the hyperbase layer and fully attend to application and user interface issues. Design, development, and deployment experiences of a dynamic, open, and distributed multiuser hypermedia system development environment called Hyperform is presented. Hyperform is based on the concepts of extensibility, tailorability, and rapid prototyping of hypermedia system services. Open, extensible hyperbase management systems permit hypermedia system developers to tailor hypermedia functionality for specific applications and to serve as a platform for research. The Hyperform development environment is comprised of multiple instances of four component types: (1) a hyperbase management system server, (2) a tool integrator, (3) editors, and (4) participating tools. Hyperform has been deployed in Unix environments, and experiments have shown that Hyperform greatly reduces the effort required to provide customized hyperbase management system support for distributed multiuser hypermedia systems.

Measuring Link Importance in Terrorist Networks

A terrorist network is a special kind of social network with emphasis on both secrecy and efficiency. Such networks are intentionally structured to ensure efficient communication between members without being detected. A terrorist network can be modeled as a generalized network (graph) consisting of nodes and links. Techniques from social network analysis and graph theory can be used to identify key entities in the network, which is helpful for network destabilization purposes. Research on terrorist network analysis has mainly focuses on analysis of nodes, which is in contrast to the fact that the links between the nodes provide at least as much relevant information about the network as the nodes themselves. This paper presents a novel method to analyze the importance of links in terrorist networks inspired by research on transportation networks. The link importance measure is implemented in CrimeFighter Assistant and evaluated on known terrorist networks.