Hypermedia Research Directions:
An Infrastructure Perspective
Uffe K. Wiil,
Peter J. Nürnberg
Department of Computer Science Web: http://www.cs.aue.auc.dk/
Niels Bohrs Vej 8, 6700 Esbjerg, Denmark
Email: ukwiil@cs.aue.auc.dk, pnuern@daimi.au.dk
Web: http://www.cs.aue.auc.dk/~kock, http://www.cs.aue.auc.dk/~pnuern/ Texas A&M University Web: http://www.tamu.edu/
Department of Computer Science Web: www.cs.tamu.edu/
College Station, TX 77843-3112, USA
Email: leggett@csdl.tamu.edu
Web: http://www.csdl.tamu.edu/~leggett
Abstract: This paper offers a perspective on the directions in which hypermedia infrastructure research will move in the next several years. The perspective is based on the authors' experiences and insights from a decade of active participation in this research area. After a review of hypermedia infrastructure research, the paper focuses on two particular threads of such research named "multiple open services" and "structural computing". We believe that these threads show much promise for the future.Categories and Subject Descriptors: H.5.4 [Information Interfaces and Presentation]: Hypertext/Hypermedia - Architectures
General Terms: Design, Experimentation, Standardization
Additional Key Words and Phrases: open hypermedia system (OHS), component-based open hypermedia system (CB-OHS), multiple open services, structural computing, hypermedia operating system (HMOS)
1 Introduction
From its inception, hypermedia has been less about adding new functionality to computer systems (e.g., the ability to link objects together) and more about changing the way computer systems work to reflect more accurately the way in which people work. Bush [Bush 1945] noted that people use associative recall to remember information, and thus proposed that our tools should mimic this functionality. Engelbart [Engelbart 1962] spoke in terms of building machines that allowed "automated external symbol manipulation" on our terms as human users, not in ways dictated to us by computers. Nelson [Nelson 1967] spoke of hypermedia environments as freeing us from the single world-view paradigm of early computers.Hypermedia structuring principles have been applied to a wide variety of application domains such as argumentation support [Conklin 1987b], [McCall 1990], digital libraries [Dewan 1995], [Schnase 1994], engineering enterprises [Grønbæk 1994a], [Malcolm 1991], information analysis [Marshall 1995], [Shipman 1995], classification [Parunak 1991], [Parunak 1993], and collaborative work [Streitz 1992], [Wiil 1992a]. The diverse and complex requirements of these domains have resulted in extensive research into hypermedia infrastructure. This paper offers our perspective on the directions in which hypermedia infrastructure research will move in the next several years. This perspective is based on our experiences and insights from a decade of active participation in this research area. After a historical review of hypermedia infrastructure research (Section 2), the paper focuses on two particular threads of such research named "multiple open services" and "structural computing". We believe that these threads show much promise for the future. The basic ideas and characteristics of multiple open services and structural computing research are described in Section 3 and Section 4, respectively. Section 5 provides our conclusions.
2 Hypermedia Infrastructure History
Hypermedia infrastructure has evolved tremendously since the first monolithic system architectures were developed in the 1960s. Current hypermedia infrastructure is more open and modular with general and extensible system components that provide well-defined services. These services are becoming increasingly standardized within the research community, as the past decade of work has led to a great deal of consensus on the form of at least the most common of them [Wiil 1997b], [Wiil 1998], [Wiil 1999a]. Figure 1 depicts four different stages of development in the evolution of hypermedia infrastructure. Figure 2 presents a historical view of some of the more prominent hypermedia infrastructure research directions and their mutual relationships.
Figure 1. Different stages of development in the evolution of hypermedia infrastructure (inspired by similar figures in [Nürnberg 1997a], [Nürnberg 1998] and [Wiil 1999b]). A shaded box indicates the closed part(s) of the infrastructure - implemented by a single (type of) process.
The earliest hypermedia systems were monolithic [Akscyn 1988] [Engelbart 1962] [Halasz 1987] (Figure 1a). A monolithic system includes all system services in a single process (application, link service and store). In 1987, system developers began to publish results on new types of hypermedia systems: link server systems (LSS) and hyperbase management systems (HBMS). Both of these types of systems are based on client-server architectures (Figure 1b). A client-server system operates with a single server process that includes link service and store functionality. An open set of applications can access the server functionality. Meyrowitz [Meyrowitz 1989] and Pearl [Pearl 1989] first discussed research on LSS. Later, several LSS emerged, including PROXHY [Kacmar 1991], Microcosm [Davis 1992], [Davis 1994], [Fountain 1990], [Hall 1996], Multicard [Rizk 1992], Chimera [Anderson 1994], Hyper-G [Maurer 1996], and KHS [Rittberger 1994]. Research on HBMS was first reported by Campbell and Goodman [Campbell 1987]. Later, five HBMS research groups were active: GMD-IPSI [Bapat 1996], [Schütt 1990], [Schütt1993], Aarhus University [Grønbæk 1994a], [Grønbæk 1994b], University of North Carolina [Shackelford 1993], [Smith 1991], Texas A&M University [Leggett 1994], [Nürnberg 1996], [Schnase 1992], [Schnase 1993a], and Aalborg University [Wiil 1992b], [Wiil 1997a], [Wiil 1993]. In 1994, people from the HBMS and LSS areas joined to form the Open Hypermedia System (OHS) research thread [Wiil 1994], [Wiil 1996a], [Wiil 1997b], [Wiil 1998], [Wiil 1999a]. OHS mostly focus on providing link services to an open set of applications (Figure 1c). The enormous success of the World Wide Web (WWW) [Berners-Lee 1994] has resulted in a separate research thread focusing on integration of OHS with WWW browsers such as Netscape and MS Internet Explorer. Since 1995, many OHS have been integrated with the WWW to provide "external linking" as opposed to the "embedded linking" style available in the unaugmented WWW [Anderson 1997], [Carr 1995], [Grønbæk 1997].
Figure 2. A historical view of hypermedia infrastructure research (updated from Figure 1 in [Wiil 1997a]).
Research on component-based open hypermedia systems (CB-OHS) grew out of the early OHS research. Two different types of CB-OHS (Figure 1d) exist. Multiple open services work was first discussed in 1995 in connection with HyperDisco [Wiil 1995], which provides different types of link, integration, distribution, and collaboration services [Wiil 1996], [Wiil 1997a]. Structural computing work was first discussed in 1996 in the initial HOSS paper [Nürnberg 1996]. In 1997, the HOSS project reported first results of provision of different types of hypermedia structure services (i.e., linking, spatial and taxonomic) [Nürnberg 1997a], [Nürnberg 1997b] backed by a "hypermedia operating system" (HMOS).
3 Multiple Open Services
A multiple open services environment is a CB-OHS that consists of two types of components. Structure-aware stores provide core hypermedia services (i.e., objects, attributes, behaviors and relations), and core collaboration services (i.e., transactions, concurrency control, notification control, access control, and version control) to an open set of middleware components [Bernstein 1996], [Wiil 1999b]. Each middleware component provides a specific set of services to an open set of participating applications such as hypermedia structure, collaboration (CSCW), storage, information retrieval (IR), integration and interoperability, and versioning services.Middleware services can be divided into "infrastructure" and "application" services. Infrastructure middleware services encompass those that deal with the operation of the overall multiple open services environment, and thus are used only indirectly by applications (e.g., storage, location, interoperability, heterogeneity, and distribution). Application middleware services are directly used by applications (e.g., integration, hypermedia structure, CSCW, IR, and versioning services).
A multiple open service environment has three characteristics that allow it to provide generally applicable middleware services.
Firstly, middleware services are hosted in an open architectural framework. An open architecture consists of an open set of inter-operating components. Each component provides a set of well-defined services through a well-defined interface. An open architecture is based on a "plug and play" metaphor for changes to the architecture allowing: insertion of new components with new services; replacement of existing components by new; and, removal of existing components.
Secondly, the provided middleware services must themselves be open. An open service is available to an open set of applications in the computing environment. Services are provided by computing entities or components in the computing environment that are accessible by essentially all applications (e.g., middleware or operating system components). An open service is orthogonal to other services used by participating applications (e.g., storage and display services). Applications must able to use an open service without altering the existing use of services by the application. It is general enough to be useful across applications. The service is operational both internally in the application and across to other applications of the same type or other types (e.g., "cut, copy and paste" services). An open service provides different levels of its services. Applications need not integrate advanced levels of a service if only a basic level is desired.
Finally, the middleware services are available on most major computing platforms such as Suns, PCs and Macintoshes, for most major operating systems such as Unix, Windows, and MacOS, and to applications written in many different programming languages.
4 Structural Computing
Structural computing describes the view that structural abstractions should constitute the fundamental building block of CB-OHS. Instead of speaking only in terms of structure-aware stores, structural computing systems describe entirely structure-aware OS, or HMOS. Such HMOS take to the logical extreme the trend toward making structure awareness increasingly pervasive. In HMOS, structure is all-pervasive, and replaces the data-based abstractions of traditional systems. Instead of entities (applications and middleware) mapping structural abstractions into the data abstractions of traditional operating systems and infrastructures (which is done idiosyncratically), HMOS entities map data into the provided structural abstractions, which can be done in a well-defined manner.Since structural computing CB-OHS backends provide structural abstractions to their clients, all middleware services are seen as structure services. For the services "traditionally" described in the hypermedia field, such as navigational hypermedia services (i.e., building associations among data) [Bush 1945], [Nelson 1967] or spatial hypermedia services (i.e., using flexible, dynamic structuring mechanisms to organize data) [Halasz 1987], [Marshall 1995], this structure-intensive view has clear and immediate benefits. The hypermedia field has long accepted that the design and implementation of such a hypermedia service can be accomplished more quickly and efficiently on a structure-aware backend [Wiil 1999b]. Additionally, provision of such hypermedia services within a common framework, such as that provided by CB-OHS, allows for intra- and inter-domain interoperability. Since structure representation is supported at such a low level in the system, all services in an environment can use and understand the use of such facilities.
Structural computing posits additionally, however, that the design and implementation of arbitrary services accrue these same benefits on such an infrastructure. Clearly, no service is made more difficult to design or implement in a structural computing CB-OHS. Those services currently based on traditional data abstractions can be ported to a structural computing CB-OHS by simply ignoring the structure representation mechanisms supported by the HMOS. However, we assert that a wide variety of such data-oriented services can in fact be usefully reconceptualized as structure services. For example, consider the memory management service prefetching. Prefetching algorithms use the notion of semantic locality to predict which pages are most likely to be referenced in the near future. Semantic locality can only be inferred indirectly in traditional systems by measures such as virtual address space proximity. In a structural computing CB-OHS, with its structure-aware HMOS, the prefetching service is a structure service, and is therefore guaranteed to be able to understand structure among objects represented in pages, which are generally a direct measure of semantic relatedness (and thus locality) [Nürnberg 1996].
5 Conclusion
Early hypermedia work assumed that building hypermedia systems was a matter of building the correct interface to computers. However, our field has moved toward the view that hypermedia interfaces require hypermedia infrastructure. CB-OHS are the latest attempt to supply such infrastructures. There are two important directions in this work. A multiple open services environment focuses on what services should be supplied by such an infrastructure; structural computing focuses on how such services should be conceived.References
[Akscyn 1988] Robert M. Akscyn, Donald L. McCracken, and Elise A. Yoder. "KMS: A Distributed Hypermedia System for Managing Knowledge in Organizations" in Communications of the ACM (CACM), 31(7), 820-835, July 1988.[Anderson 1994] Kenneth M. Anderson, Richard N. Taylor, and E. James Whitehead. "Chimera: Hypertext for Heterogeneous Software Environments" in Proceedings of the ACM European Conference on Hypermedia Technology (ECHT '94), Edinburgh, Scotland, 94-106, [Online: http://acm.org/pubs/citations/proceedings/hypertext/192757/p94-anderson/], September 1994.
[Anderson 1997] Kenneth M. Anderson. "Integrating Open Hypermedia Systems with the World Wide Web" in Proceedings of ACM Hypertext '97, Southampton UK, 157-167, [Online: http://acm.org/pubs/citations/proceedings/hypertext/267437/p157-anderson/], April 1997.
[Bapat 1996] Ajit Bapat, Jurgen Wäsch, Karl Aberer, and Jörg M. Haake. "HyperStorM: An Extensible Object-Oriented Hypermedia Engine" in Proceedings of ACM Hypertext '96, Washington, DC, 203-214, March 1996.
[Berners-Lee 1994] Tim J. Berners-Lee, Robert Cailliau, Ari Luotonen, H. Frystyk Nielsen, and Arthur Secret. "The World-Wide Web" in Communications of the ACM (CACM), 37(8), 76-82, 1994.
[Bernstein 1996a] Philip A. Bernstein. "Middleware: A Model for Distributed System Services" in Communications of the ACM (CACM), 39(2), 86-98, 1996.
[Bush 1945] Vannevar Bush. "As We May Think" in The Atlantic Monthly, 176(1),101-108, [Online: http://www.isg.sfu.ca/~duchier/misc/vbush/], July 1945.
[Campbell 1987] Bruce Campbell and Joseph M. Goodman. "HAM: A General-Purpose Hypertext Abstract Machine" in Proceedings of ACM Hypertext '87, Chapel Hill, NC, 21-32, November 1987.
[Carr 1995] Leslie A. Carr, David C. DeRoure, Wendy Hall, and Gary J. Hill. "The Distributed Link Service: A Tool for Publishers, Authors, and Readers" in Proceedings of the Fourth International World Wide Web Conference, Boston, MA, 647-656, [Online: http://www.staff.ecs.soton.ac.uk/lac/dls/link_service.html], December 1995.
[Conklin 1987b] Jeff Conklin and Michael L. Begeman. "gIBIS: A Hypertext Tool for Design Deliberation" in Proceedings of ACM Hypertext '87, Chapel Hill, NC, 247-251, March 1987.
[Davis 1992] Hugh C. Davis, Wendy Hall, Ian Heath, Gary J. Hill, and Rob J. Wilkins. "Towards an Integrated Information Environment with Open Hypermedia Systems" in Proceedings of the ACM Conference on Hypertext (ECHT '92), Milano, Italy, 181-190, [Online: http://acm.org/pubs/citations/proceedings/hypertext/168466/p181-davis/], December 1992.
[Davis 1994] Hugh C. Davis, Simon Knight, and Wendy Hall. "Light Hypermedia Link Services: A Study of Third-Party Application Integration" in Proceedings of ACM European Conference on Hypermedia Technologies (ECHT)'94, Edinburgh, Scotland, 41-50, September 1994.
[Dewan 1995] Prasun Dewan, Kevin Jeffay, John Smith, P. David Stotts, and William Oliver, W. 1995. Early Prototypes of the Repository for Patterned Injury Data" in Proceedings of ACM Digital Libraries '95, Austin, TX, 123-130, June 1995.
[Engelbart 1962] Douglas C. Engelbart. Augmenting Human Intellect: A Conceptual Framework. Technical Report AFOSR-3223, Contract AF 49(638)-1024, Stanford Research Institute (SRI), 1962.
[Fountain 1990] Andrew M. Fountain, Wendy Hall, Ian Heath, Hugh C. Davis. "Microcosm: An Open Model With Dynamic Linking" in Proceedings of the ACM European Conference on Hypertext '90 (ECHT '90), Versailles, France, 298-311, November 1990.
[Grønbæk 1994a] Kaj Grønbæk, Jens A.Hem, Ole L. Madsen, and Lennert Sloth. "Designing Dexter-based Cooperative Hypermedia Systems. Communications of the ACM (CACM), 37(2), 64-74, February 1994.
[Grønbæk 1994b] Kaj Grønbæk and Randall H. Trigg. "Design Issues for a Dexter-Based Hypermedia System" in Communications of the ACM (CACM), 37(2), 40-49, February 1994.
[Grønbæk 1997] Kaj Grønbæk, Niels Olof Bouvin, Lennert Sloth. "Designing Dexter-Based Hypermedia Services for the World Wide Web" in Proceedings of ACM Hypertext '97, Southamption, UK, 146-156, [Online: http://acm.org/pubs/citations/proceedings/hypertext/267437/p146-gronbaek/], 1997
[Halasz 1987] Frank G. Halasz, Thomas P. Moran and Randall H. Trigg. "NoteCards in a Nutshell" in Proceedings of the ACM CHI+GI '87, Toronto, Canada, 345-365, April 1987.
[Hall 1996] Wendy Hall, Hugh C. Davis, and Gerard Hutchings. Rethinking Hypermedia, The Microcosm Approach. Kluwer Academic, Dordrecht, The Netherlands, 1996.
[Kacmar 1991] Charles J. Kacmar and John J. Leggett. "PROXHY: A Process-oriented Extensible Hypertext Architecture" in ACM Transactions on Information Systems (TOIS), 9(4), 399-419, 1991.
[Leggett 1994] John J. Leggett and John L. Schnase. "Viewing Dexter with Open Eyes" in Communications of the ACM (CACM), 37(2), 76-86, 1994.
[Malcolm 1991] Kathryn C. Malcolm, Steven E. Poltrock, and Douglas Schuler. "Industrial Strength Hypermedia: Requirements for a Large Engineering Enterprise" in Proceedings of ACM Hypertext '91, San Antonio, TX, 13-24, 1991.
[Marshall 1995] Catherine C. Marshall, and Frank M. Shipman. "Spatial Hypertext: Designing for Change" in Communications of the ACM (CACM), 38(8), 88-97, August 1995.
[Maurer 1996] Hermann A. Maurer. Hyper-G now Hyperwave : The Next Generation Web Solution, Addison Wesley Longman, ISBN 0‚201‚40346‚3, 1996.
[McCall 1990] Raymond J. McCall, Patrick R. Bennett, Peter S. d'Oronzio, Jonathan L. Ostwald, Frank M. Shipman, and Nathan F. Wallace. "PHIDIAS: Integrating CAD graphics into dynamic hypertext" in Proceedings of the ACM European Conference on Hypertext '90 (ECHT '90), Versailles, France, 152-165, November 1990.
[Meyrowitz 1989] Norman K. Meyrowitz "The Missing Link: Why We're All Doing Hypertext Wrong" in The Society of Text: Hypertext, Hypermedia, and the Social Construction of Information, Edward Barrett (editor), Cambridge, MA: MIT Press, 107-114, 1989.
[Nürnberg 1996] Peter J. Nürnberg, John J. Leggett, Erich R. Schneider, and John L. Schnase. " HOSS: A New Paradigm for Computing" in Proceedings of ACM Hypertext '96, Washington, DC, 194-202, March 1996.
[Nürnberg 1997a] Peter J. Nürnberg, John Leggett, and Erich R. Schneider. "As We Should Have Thought" in Proceedings of ACM Hypertext '97, Southampton, UK, 96-101, April 1997.
[Nürnberg 1997b] Peter J. Nürnberg and John J. Leggett. "A Vision for Open Hypermedia Systems" in Journal of Digital Information, 1(2), 1997.
[Nürnberg 1998] Peter J. Nürnberg, John J. Leggett, and Uffe K. Wiil, "An Agenda for Open Hypermedia Research" in Proceedings of ACM Hypertext '98, Pittsburgh, PA, 198-206, [Online: http://acm.org/pubs/citations/proceedings/hypertext/276627/p198-nurnberg/], June 1998.
[Nelson 1967] Theodor Helm Nelson. "Getting it out of our system" in Information Retrieval: A Critical View, G. Shector, (editor), Thompson Book Co., Washington, DC, 191-210, 1967.
[Parunak 1991] H. van Dyke Parunak. " Don't Link Me In: Set-based Hypermedia for Taxonmoic Reasoning" in Proceedings of ACM Hypertext '91, San Antonio, TX, 233-242, [Online: http://acm.org/pubs/citations/proceedings/hypertext/122974/p233-van_dyke_parunak/], December 1991.
[Parunak 1993] H. van Dyke Parunak. "Hypercubes grow on trees (and other observations from the land of hypersets)" in Proceedings of ACM Hypertext '93, Seattle, WA, 73-81, November 1993.
[Pearl 1989] Amy Pearl. "Sun's Link Service: A Protocol for Open Linking" in Proceedings of ACM Hypertext '89, Pittsburgh, PA, 137-146, November 1989.
[Rittberger 1994] Marc Rittberger, Rainer Hammw–hner, Rolf Aţfalg, and Rainer Kuhlen. "A homogeneous interaction platform for navigation and search in and from open hypertext systems" in Proceedings of RIAO '94, New York, NY, 649-663, October 1994.
[Rizk 1992] Antoine Rizk, and Louis Sauter. "Multicard: An Open Hypermedia System" in Proceedings of the ACM Conference on Hypertext (ECHT '92), Milano, Italy, 4-10, [Online: http://acm.org/pubs/citations/proceedings/hypertext/168466/p4-rizk/], December 1992.
[Schütt 1990] Helge Schütt and Norbert A. Streitz. "Hyperbase: A hypermedia engine based on a relational database management system" in Proceedings of the ACM European Conference on Hypertext '90 (ECHT '90), Versailles, France, 95-108, November 1990.
[Schütt 1993] Helge Schütt and Jörg M. Haake. "Server support for cooperative hypermedia systems. In Proceedings of Hypermedia '93, (Zurich, Switzerland, Mar), Springer Verlag, 45-56.
[Schnase 1992] John L. Schnase. HB2: A Hyperbase Management System for Open, Distributed Hypermedia System Architectures. Ph.D. Dissertation, Texas A&M University, College Station, TX, 1992.
[Schnase 1993a] John L. Schnase, John J. Leggett, David L. Hicks, Peter J. Nürnberg, and J. Alfredo S·nchez. "Design and Implementation of the HB1 Hyperbase Management System" in Electronic Publishing: Origination, Dissemination and Design, 6(2), 35-63, 1993.
[Schnase 1994] John L. Schnase, John J. Leggett, Ted Metcalfe, Nancy R. Morin, Edward L. Cunnius, Jonathan S. Turner, Richard K. Furuta, Leland Ellis, Michael S. Pilant, Richard E. Ewing, Scott W. Hassan, and Mark E. Frisse. "The CoLib Project: Enabling Digital Botany for the 21st Century" in Proceedings of ACM Digital Libraries '94, College Station, TX, 108-118, June 1994.
[Shackelford 1993] Douglas E. Shackelford, John B. Smith, and F. Donelson Smith. "The Architecture and Implementation of a Distributed Hypermedia Storage System" in Proceedings of ACM Hypertext '93, Seattle, WA, 1-13, November 1993.
[Shipman 1995] Frank M. Shipman, Catherine C. Marshall, and Thomas P. Moran. "Finding and Using Implicit Structure in Human-Organized Spatial Layouts of Information" in Proceedings of ACM SIGCHI '95, Denver, CO, 346-353, May 1995.
[Smith 1991] John B. Smith and F. Donelson Smith. "ABC: A Hypermedia System for Artifact-Based Collaboration" in Proceedings of ACM Hypertext '91, San Antonio, TX, 179-192, December 1991.
[Streitz 1992] Norbert A. Streitz, Jörg M. Haake, Jörg Hannemann, Andreas Lemke, Wolfgang Schuler, Helge Schütt and Manfred Thüring. "SEPIA: A Cooperative Hypermedia Authoring Environment" in Proceedings of the ACM Conference on Hypertext (ECHT '92), Milano, Italy, 11-22, December 1992.
[Wiil 1992a] Uffe K. Wiil. "Issues in the Design of EHTS: A Multiuser Hypertext System for Collaboration" in Proceedings of the IEEE Hawaii International Conference on System Sciences '92, Kauai, HI, 2, 629-639, 1992.
[Wiil 1992b] Uffe K. Wiil and John J. Leggett. "Hyperform: Using Extensibility to Develop Dynamic, Open, and Distributed Hypertext Systems" in Proceedings of the ACM Conference on Hypertext (ECHT '92), Milano, Italy, 251-261, December 1994.
[Wiil 1993] Uffe K. Wiil. "Experiences with HyperBase: A Multiuser Hypertext Database" in ACM SIGMOD RECORD, 22(4), 19-25, 1993.
[Wiil 1994] Uffe K. Wiil and Kasper Østerbye (editors). Proceedings of the 1st Workshop on Open Hypermedia Systems. Technical Report R-94-2038, Department of Computer Science, Aalborg University, 1994.
[Wiil 1995] Uffe K. Wiil. "HyperDisco: An Object-Oriented Hypermedia Framework for Flexible Software System Integration" in Proceedings of IEEE Computer Software & Applications '95, Dallas, TX, 298-305, August 1995.
[Wiil 1996] Uffe K. Wiil and John J. Leggett. "The HyperDisco Approach to Open Hypermedia Systems" in Proceedings of ACM Hypertext '96, Washington DC, 140-148, [Online: http://acm.org/pubs/citations/proceedings/hypertext/234828/p140-wiil/], March 1996.
[Wiil 1996a] Uffe K. Wiil and Serge Demeyer (editors). Proceedings of the 2nd Workshop on Open Hypermedia Systems. Technical Report UCI-ICS 96-10, University of California, Irvine, 1996.
[Wiil 1997] Uffe K. Wiil and John J. Leggett. "Workspaces: The HyperDisco Approach to Internet Distribution" in Proceedings of ACM Hypertext 97, Southampton, UK, 13-23, [Online: http://acm.org/pubs/citations/proceedings/hypertext/267437/p13-wiil/], April 1997.
[Wiil 1997a] Uffe K. Wiil and John J. Leggett. "Hyperform: A Hypermedia System Development Environment" in ACM Transactions on Information Systems (TOIS), 15(1), 1-31, 1997.
[Wiil 1997b] Uffe K. Wiil (editor). Proceedings of the 3rd Workshop on Open Hypermedia Systems. CIT Scientific Report SR-97-01, The Danish National Centre for IT Research, 1997.
[Wiil 1998] Uffe K. Wiil (editor). Proceedings of the 4th Workshop on Open Hypermedia Systems. Technical Report CS-98-01, Aalborg University Esbjerg, 1998.
[Wiil 1999a] Uffe K. Wiil (editor). Proceedings of the 5th Workshop on Open Hypermedia Systems. Technical Report CS-99-01, Aalborg University Esbjerg, 1999.
[Wiil 1999b] Uffe K. Wiil and Peter J. Nürnberg. "Evolving Hypermedia Middleware Services: Lessons and Observations" in Proceedings of the ACM Symposium on Applied Computing '99, San Antonio, TX, 427-436, February 1999.