Lennert Sloth

Designing Dexter-based hypermedia services for the World Wide Web

This paper discusses how to augment the WWW with a Dexter-based hypermedia service that provides anchors, links and composites as objects stored external to the Web pages. The hypermedia objects are stored in an objectoriented database that is accessible on the Web via an ordinary URL. The Dexter-based hypermedia service is based on the Devise Hypermedia framework. Three client solutions are described and discussed, one that is platform independent based on Netscape Navigator 3.0, utilizing Java, Javascript, and LiveConnect, and two that are platform dependent, one utilizing Netscape plug-ins, and another using Microsoft Internet Explorer 3.0, utilizing mainly ActiveX. The server part is developed as a specialization of the Devise Hypermedia framework accessible through CGI scripts. Thus the system provides the full power of Dexter-based hypermedia to arbitrary Web pages on the Internet. This includes the ability for multiple users to create links from parts of HTML Web pages they do not own and support for creating links to parts of Web pages without writing HTML target tags. Support for providing links to/from parts of non-HTML data, such as Quicktime movies or VRML documents will also be possible in the future provided that appropriate open plug-in modules become available.

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.

A metro map metaphor for guided tours on the Web: the Webvise guided tour system

This paper presents a guided tour system for the WWW. It is a module for the Webvise open hypermedia system that implements the ideas of trails and guided tours, originating from the hypertext field. Webvise appears as an open hypermedia helper application to the user and stores the guided tours in an XML format called OHIF separated from the WWW documents included in the tour. The main advantages of the system are: (1) a browser independent format in terms of HTML and PNG-based image maps for reading the guided tours; (2) support for a familiar metaphor, namely, a metro route map; (3) overview maps and route maps with indication of which stations of a tour have been visited; and finally (4) support for arbitrary web pages as stations on the tour. The paper discusses the Webvise Guided Tour System and illustrates its use in a digital library portal. The system is compared to other recent Web-based guided tour systems, and it is argued that Webvise Guided Tour System solves a number of prior system problems.

Open hypermedia as user controlled meta data for the Web

Abstract This paper introduces an approach to utilise open hypermedia structures such as links, annotations, collections and guided tours as meta data for Web resources. The paper introduces an XML based data format, called Open Hypermedia Interchange Format, OHIF, for such hypermedia structures. OHIF resembles XLink with respect to its representation of out-of-line links, but it goes beyond XLink with a more rich set of structuring mechanisms, including e.g. composites. Moreover OHIF includes an addressing mechanisms (LocSpecs) that goes beyond XPointer and URL in its ability to locate non-XML data segments. By means of the Webvise system, OHIF structures can be authored, imposed on Web pages, and finally linked on the Web as any ordinary Web resource. Following a link to an OHIF file automatically invokes a Webvise download of the meta data structures and the annotated Web content will be displayed in the browser. Moreover, the Webvise system provides support for users to create, manipulate, and share the OHIF structures together with custom made Web pages and MS Office 2000 documents on WebDAV servers. These Webvise facilities goes beyond earlier open hypermedia systems in that it now allows fully distributed open hypermedia linking between Web pages and WebDAV aware desktop applications. The paper describes the OHIF format and demonstrates how the Webvise system handles OHIF. Finally, it argues for better support for handling user controlled meta data, e.g. support for linking in non-XML data, integration of external linking in the Web infrastructure, and collaboration support for external structures and meta-data.

Designing Dexter-based cooperative hypermedia systems

This paper discusses issues for the design of a Dexter-based cooperative hypermedia architecture and a specific system, DeVise Hypermedia (DHM), developed from this architecture. The Dexter Hypertext Reference Model [Hala90] was used as basis for designing the architecture. The Dexter model provides a general and solid foundation for designing a general hypermedia architecture. It introduces central concepts and proposes a layering of the architecture. However, to handle cooperative work aspects, such as sharing material and cooperative authoring, we have to go beyond the Dexter model concepts. To deal with such aspects we have extended our implementation of the Dexter concepts with support for long-term transactions, locking and event notification as called for by Halasz [Hala88]. The result is a platform independent architecture for developing cooperative hypermedia systems. The architecture consists of a portable kernel that constitutes an object oriented framework for developing Dexter compliant hypermedia systems. It is a client/server architecture including an object oriented database (OODB) to store the objects implementing the Dexter Storage Layer. We use a general OODB being codeveloped to support long term transactions, flexible locking, and event notification. The transaction and locking mechanism support several modes of cooperation on shared hypermedia materials, and the notification mechanism supports the users in maintaining awareness of each othersO activity. The portable kernel was used to implement the DHM system on two quite different platforms: UNIX/X-windows and Apple Macintosh.