DHM is developed in the Mjølner BETA system. See the BETA Info page. A commercial hypermedia product, Hypervise has been developed with the Devise Hypermedia Framework. The development has been supported by the the EuroCODE project.
DESCRIPTION
The DHM framework supports development of distributed applications for:
* organizing information nodes in networks--hypertexts--of associative references, called links
* nodes may be text, graphics, video, sound - parts of nodes, e.g. sentences in a text can be anchored as endpoints of links
* integration of existing third party applications, e.g. spreadsheets.
* asynchronous cooperative work on shared hypertexts, e.g. maintaining access rights, notifying users about changes to shared hypertexts, and tracing history of information.
Applications developed with DHM are well suited for management of shared materials such as technical documentation and case material. Information can be stored in the most convenient fashion and DHM offers support for navigation through the information network, by means of link following and browsing.
The DHM Framework is developed as an object-oriented interpretation and extension of the Dexter Hypertext Reference Model which is a popular model covering ideas and experiences from leading hypermedia research.
Links:
DHM supports bi-directional links with multiple endpoints. Endpoints can be entire nodes or anchored parts of node contents. Links can be followed with a single operation on a selected link marker, and they can be inspected and edited in editors and browsers.
Cooperation:
The DHM uses an Object-Oriented Database (OODB) to provide cooperation support for shared hypertexts. The OODB supports long-term transactions, flexible locking, and notification about events occurring on shared objects. This enables support for asynchoronous cooperation.
Indicating an event notification on a Text Component icon by a bell.
WORKING COMPONENTS
The DHM Framework is organized in four conceptual layers. The STORAGE, RUNTIME, and PRESENTATION layers represent DHM class hierarchies, whereas the APPLICATION layer represents the diverse space of applications, editors or viewers that can be integrated with the DHM.
The STORAGE layer classes represents the schema for objects to be stored in the OODB. A central class here is the Component, an abstraction covering both nodes and links. The RUNTIME layer classes represent the generic behaviour of hypermedia systems. A central class here is the Instantiation class which represents behaviour for a component, including link following and handling of event notifications and locks for the component. The PRESENTATION layer classes encapsulates communication to applications from the APPLICATION layer and provides a uniform interface to these applications. The APPLICATION layer represents the space of objects or applications which can be integrated with the DHM.
EXAMPLE OF USE
A programmer can use the DHM environment to build cooperative hypermedia systems integrating an unlimted set of media types by means of one homogeneous hypermedia service. A system built from the DHM framework always provides the generic linking and cooperation support facilities.
To develop a customized hypermedia system, a programmer can start from scratch using the DHM framework; or take the source for an existing DHM system and integrate new media-types. In both cases, the programmer has to model media-types for the system by specializing DHM classes and set up a communication to the PRESENTATION layer. For instance, integrating a drawing editor requires writing of the classes depicted in blue below.
DHM example applications are provided and include the following components:
* Draw components supporting links to graphical objects.
* Text components supporting span to span links.
* Movie components supporting links to digitized video.
* File components support linking to arbitrary files.
* TableTop composites to save configurations of components to be presented together.
* Search composites collecting all the hits by queries.
* Link Composites to collect Link components.
IMPLEMENTATIONS
The DHM framework is written in the Mjølner BETA system, it is platform independent, and it is supported for UNIX/Motif, Windows/NT and 4.0 (under development) , and Apple Macintosh.
Kaj Grønbæk, Computer Science Department, Aarhus University, Ny Munkegade, Bldg. 540, DK-8000 Aarhus C, Denmark, Email: kgronbak@daimi.aau.dk, FAX: +45 8942 3255, Phone: +45 8942 3237. Mjølner Informatics, Science Park Aarhus, Gustav Wiedsvej 10, DK-8000 Aarhus C. Denmark. Email: info@mjolner.dk FAX: +45 8620 1222, Phone: +45 8620 2000
Grønbæk, K., Hem, J.A., Madsen, O.L., and Sloth, L.Cooperative Hypermedia Systems: A Dexter-based architecture. Communications of the ACM 37, 2 (Feb. 1994), pp. 64-75.
Grønbæk, K. and Trigg, R.H. Design issues for a Dexter-based hypermedia system. Communications of the ACM 37, 2 (Feb. 1994), pp. 40-49.
Grønbæk, K. and Trigg, R.H. Hypermedia System Design Applying the Dexter Model Guest editors' introduction to the special issue on Hypermedia in Communications of the ACM 37, 2 (Feb. 1994), pp. 26-29.
Grønbæk, K., Kyng, M., and Mogensen, P. CSCW challenges in large-scale technical projects - a case study. In Proceedings of Conference on Computer Supported Cooperative Work (CSCW `92), Toronto, Ontario, November, 1992. ACM, New York, pp. 338-345.
Grønbæk, K. and Trigg, R.H. Design issues for a Dexter-based hypermedia system. In Proceedings of the European Conference on Hypertext 1992 (ECHT `92). Milano, Italy, November/December 1992. ACM New York, pp 191 - 200.
Grønbæk, K., Hem, J.A., Madsen, O.L., and Sloth, L. Designing Dexter-based Cooperative Hypermedia Systems. In Proceedings of the ACM Hypertext `93 Conference, November 14-18 1993. Seattle, USA: ACM.
Grønbæk, K. and Malhotra, J. Building Tailorable Hypermedia Systems: The embedded-interpreter approach. To appear in proceedings of the ACM conference on Object Oriented Programming Systems, Languages and Applications (OOPSLA `94). Portland, Oregon, 23-27 October, 1994.
Grønbæk, K. and Mogensen, P. Specific cooperative analysis and design in general hypermedia development. To appear in Proceedings of the Participatory Design Conference (PDC '94), Chapel Hill, North Carolina, USA, October 27-28, 1994. Computer Professionals for Social Responsibility.
Grønbæk, K. Composites in a Dexter-Based Hypermedia Framework. In proceedings of the ACM European Conference on Hypermedia Technology (ECHT '94) Edinburg, UK, September 18-23, 1994.
