Multiple Open Services in a Structural Computing Environment

Transcription

1 Multiple Open s in a Structural Computing Environment Uffe K. Wiil Department of Computer Science Aalborg University Esbjerg Niels Bohrs Vej Esbjerg, Denmark ukwiil@cs.aue.auc.dk ABSTRACT This position paper argues that the structural computing workshop should cover more research ground than just structural computing s. The ongoing research thread on multiple open service s is close related to the structural computing s research thread, and as such is very relevant to the workshop. The paper starts with a historical perspective on hypermedia infrastructure research as an attempt to place current research on structural computing s and multiple open service s in context. The remainder of the paper focuses on multiple open service s. The basic ideas, goals and characteristics of multiple open service s are described. Keywords: hypermedia infrastructure, multiple open service s, structural computing s 1. INTRODUCTION Hypermedia concepts and services have over the years been incorporated into and deployed in a variety of information s including knowledge management s (e.g., [1,19]), argumentation support s (e.g., [9,26]), software development environments (e.g., [2,58]), large engineering enterprises (e.g., [15,23]), collaborative authoring s (e.g., [45,46]), taxonomic s (e.g., [32,33]), information analysis s (e.g., [24,43]), the World Wide Web [5], and digital library s (e.g., [12,39]). The diverse and complex requirements of these application domains have resulted in extensive research into advanced hypermedia infrastructure that can provide the necessary hypermedia services. This position paper argues that the structural computing workshop should cover more research ground than just structural computing s. The ongoing research thread on multiple open service s is close related to the structural computing s research thread, and as such is very relevant to the workshop. The paper starts with a historical perspective on hypermedia infrastructure research as an attempt to place current research on structural computing s and multiple open service s in context (Section 2). The remainder of the paper focuses on multiple open service s. The basic ideas, goals and characteristics of multiple open service s are described in Section 3. Finally, Section 4 provides some conclusions. 2. EVOLUTION OF HYPERMEDIA INFRASTRUCTURE Hypermedia infrastructure has evolved tremendously since the first monolithic architectures were developed in the 1960 s. Current hypermedia infrastructure is more open and modular with general and extensible components that provide well-defined services and is responsible for well-defined tasks. Figure 1 depicts five different stages of development in the evolution of hypermedia infrastructure from monolithic s (1a) to multiple open service s (1e). The immediate result of this evolution is that hypermedia infrastructure is much better geared to provide a variety of services in large and complex distributed computing settings as required by the diverse application domains. The earliest hypermedia s were monolithic (e.g., NLS/Augment [13], KMS [1] and NoteCards [19]). A monolithic is one in which all aspects of the (, Link and ) are realized in a single process (Figure 1a). At the first Hypertext Workshop in 1987, developers began to publish and distribute results on new types of hypermedia s: link server s (LSS) and hyperbase management s (HBMS). Both of these types of s are based on client server architectures (Figure 1b). Figure 2 presents a historical view of some of the more prominent hypermedia infrastructure research directions and their mutual relationships.

2 Research on LSS's was first discussed at Hypertext '87 when Meyrowitz handed out his much quoted paper: The missing link: Why we are all doing hypertext wrong (later published in [27]). The Hypertext '89 paper on Sun's Link [34] was quickly followed by papers on PROXHY [21], Microcosm [10,11,14,20] and Multicard [36]. More recently s like Chimera [2], Hyper-G [25] and KHS [35] have emerged. Research on HBMS's was first reported in the Hypertext Abstract Machine paper at Hypertext '87 [7]. By 1990 several other research groups began to publish HBMS research results. A few years later five research groups were active in the HBMS field: GMD-IPSI [4,40,41], Aarhus University [15,16], University of North Carolina [42,44], Texas A&M University [22,28,37,38], and Aalborg University [47,48,53]. Link Link Link Structure Arbitrary a) monolithic b) client server c) open hypermedia d) structural computing e) multiple open service Figure 1. Different stages of development in the evolution of hypermedia infrastructure (inspired by similar figures in [29], [31] and [57]). The focus of LSS s is to develop middleware [6] components that can provide hypermedia link services to applications orthogonal to their storage and display services. Using the services of a LSS, existing applications in the computing environment can be hypermedia enabled thus providing hypermedia linking to and from information managed by the applications without altering the information itself. Driven by the idea of a unified hypermedia environment, HBMS research has been concentrating on providing services at a more basic level. In addition to hypermedia link services, HBMS s also provide storage services. HBMS s have been used to develop middleware components that allow existing applications to use both link and storage services (if desirable). Around 1994, people from the HBMS and LSS areas joined to form the Open Hypermedia System (OHS) research thread [49,52,55,56]. Not surprisingly, the services provided by OHS s are quite diverse and can be identified as originating from either the LSS or the HBMS research thread. The common denominator among services provided by OHS s is link services, and it is fair to say that OHS s mostly focus on providing link services to an open set of applications (Figure 1c). The enormous success of the World Wide Web (WWW) has also had its impact on hypermedia infrastructure research and has resulted in a separate research thread focusing on integration of OHS s with WWW browsers such as Netscape and Microsoft Internet Explorer. Since 1995 many OHS s (e.g., Microcosm [8], DHM [17] and Chimera [3]) have been integrated with the WWW to provide external linking as opposed to the embedded linking style available in the WWW. Structural computing s (Figure 1d) and multiple open service s (Figure 1e) research both grew out of the early OHS research. The multiple open service research thread started in 1995 when first results from the HyperDisco project were reported [50]. HyperDisco [51,54] provides different types of link, integration, distribution, and collaboration services concurrently in the middleware layer. Multiple open service s are further described in Section 3. The structural computing work started in 1996 with the paper on hypermedia operating s services (HOSS) [28]. In 1997, the HOSS project [29,30] reported first results with provision of different types of hypermedia services (i.e., linking, spatial and 2

3 taxonomic structures) concurrently in the middleware layer. The term structural computing was used to describe s that provide different types of hypermedia structure services. In essence, structural computing is an attempt to broaden the scope of hypermedia infrastructure research and development to provide different structure services to a variety of application domains. World Wide Web (WWW) Hyperbase Management Systems OHS/WWW Open Hypermedia Systems (OHS) Link Server Systems Multiple Open Systems Structural Computing Systems Monolithic Hypermedia Systems Figure 2. A historical view of hypermedia infrastructure research (inspired by Figure 1 in [54]). 3. MULTIPLE OPEN SERVICE SYSTEMS A multiple open service can potentially provide many kinds of middleware services to applications such as hypermedia structure services (as in structural computing environments), collaboration (CSCW) services, storage services, information retrieval (IR) services, integration and interoperability services, versioning services, etc. Thus, the multiple open service s research thread is about more than just hypermedia it is a new interdisciplinary research thread that combines results from many research domains in an attempt to develop theories, models, standards, architectures, components, interfaces, and prototypes of general purpose middleware services. Construct [57] is a first prototypic implementation of a multiple open service. Currently, the effort is focusing on development of different hypermedia structuring services and collaboration services [18]. Preliminary research results and experiences indicate that a division of the middleware services into infrastructure and application services will provide a good starting point for research and development on multiple open service s. Infrastructure middleware services encompass services that deal with the operation of the overall multiple open service environment, and are thus only indirectly used by participating applications. These services include storage, location, interoperability, heterogeneity, and distribution services. middleware services are services directly used by participating applications. These services include integration, hypermedia structure, CSCW, IR, and versioning services. Three specific goals must be accomplished to meet the overall goal of providing generally applicable middleware services: the architectural framework in which the middleware services are provided must be open, the individual middleware services must themselves be open, and the software must be platform independent. Goal 1: Open architectural framework. An open architectural framework should host the middleware services. The identified characteristics of an open architectural framework are: An open architecture should consist of an open set of inter-operating components. Each component should provide a set of well-defined services through a well-defined interface. An open architecture should be based on a plug and play metaphor for changes to the architecture allowing: insertion of new components with new middleware services, replacing of existing components with new components, and removal of existing components. 3

4 Goal 2: Open middleware services. The provided middleware services must themselves be open. The identified characteristics of open middleware services are: An open service should be available to an open set of applications in the computing environment. The service should be provided by computing entities or components in the computing environment that are accessible by essentially all applications (e.g., middleware or operating components). An open service should be orthogonal to other services used by participating applications (e.g., storage and display services). s should be able to use the services of an open service without altering the existing services available in the application. An open service should be general enough to be useful across applications. The service should be operational both internally in the application and across to other applications of the same type or other types like for example "cut, copy and paste" services. An open service should provide different levels of its services. s should be able to get exactly what they need in terms of services and levels of services. Goal 3: Platform independence. The middleware services should not be limited to a single computing platform, operating or programming language. The identified characteristics of platform independence are that the middleware services should be available: on most major computing platforms such as Sun s, PC s and Macintosh s, for most major operating s such as Unix and Windows, and to applications written in many different programming languages. 4. CONCLUSION The research threads on structural computing s and multiple open service s both originate from the same historical line of hypermedia infrastructure research (HBMS research followed by OHS research). The research threads have been running in parallel for some time and have influenced each other. Thus, they have many things in common both attempt to build open middleware services on top of structure-aware stores. The structural computing s thread views all kinds of middleware services from a structural perspective, and hence, only talk about structure services. The multiple open service s thread distinguishes between structural and non-structural services, and hence, talks about arbitrary services. This position paper argues that the structural computing workshop should broaden its scope to also cover multiple open service s. However, several different positions can be taken with respect to the relationship between structural computing s and multiple open service s: They are actually covering the same work and should be considered part of the same research thread. They are orthogonal to each other and as such cover different aspects of hypermedia infrastructure research. Multiple open service s is a generalization of structural computing s, since structural computing s only deal with structure services and multiple open service s deal with arbitrary services. Multiple open service s research is too general to be considered hypermedia infrastructure research, while structural computing s certainly can be characterized as hypermedia infrastructure research. Structural computing s research is too limited in scope and multiple open service s research is not, since hypermedia has always been an interdisciplinary field that overlaps with many other research fields such as CSCW and IR. Maybe all these perspectives are true to some degree. Hopefully, the discussion at the structural computing workshop will bring us closer to an answer! ACKNOWLEDGMENTS The work presented in this paper was partially sponsored by the Danish National Center for IT Research though projects 123 (Coconut) and 134 (Fasit). 4

5 REFERENCES 1. Akscyn, R., McCracken D., and Yoder, E KMS: A Distributed Hypermedia System for Managing Knowledge in Organizations. Communications of the ACM, 31(7), Anderson, K., Taylor, R., and Whitehead, E. J Chimera: Hypertext for Heterogeneous Software Environments. In Proceedings of ECHT 94, (Edinburgh, Scotland, Sep), ACM Press, pp Anderson, K. M Integrating Open Hypermedia Systems with the World Wide Web. In Proceedings of Hypertext 97, (Southampton, UK, Apr), ACM Press, pp Bapat, A., Wäsch, J., Aberer, K., and Haake, J. M HyperStorM: An Extensible Object-Oriented Hypermedia Engine. In Proceedings of Hypertext 96, (Washington, DC, Mar), ACM Press, pp Berners-Lee, T., Cailliau, R., Luotonen, A., Nielsen, H. F., and Secret, A The World-Wide Web. Communications of the ACM, 37(8), Bernstein, P. A. Middleware: A Model for Distributed System s. Communication of the ACM, 39(2), Campbell, B., and Goodman, J HAM: A General-purpose Hypertext Abstract Machine. In Proceedings of Hypertext 87, (Chapel Hill, NC, Nov), ACM Press, pp Later published in Communication of the ACM, 31(7), Carr, L., De Roure, D., Hall, W., and Hill, G The Distributed Link : A Tool for Publishers, Authors and Readers. In Proceedings of WWW4, (Boston, MA, Dec), O'Reilly & Associates, pp Conklin, J. and Begeman, M gibis: A Hypertext Tool for Design Deliberation. In Proceedings of Hypertext 87, (Chapel Hill, NC, Nov), ACM Press, pp Davis, H., Hall, W., Heath, I., Hill, G., and Wilkins, R Towards an Integrated Information Environment with Open Hypermedia Systems. In Proceedings of ECHT 92, (Milan, Italy, Dec), ACM Press, pp Davis, H. C., Knight, S., Hall, W Light Hypermedia Link s: A Study of Third Party Integration. In Proceedings of ECHT 94, (Edinburgh, Scotland, Sep), ACM Press, pp Dewan, P., Jeffay, K., Smith, J., Stotts, D., and Oliver, W Early Prototypes of the Repository for Patterned Injury Data. In Proceedings of Digital Libraries 95, (Austin, TX, Jun), pp Engelbart, D. E., and English, W A Research Center for Augmenting Human Intellect. In Proceedings of the Fall Joint Computer Conference, (San Francisco, CA, Dec), AFIPS Press, pp Fountain, A. M., Hall, W., Heath, I., and Davis, H. C Microcosm: An Open Model for Hypermedia with Dynamic Linking. In Proceedings of ECHT 90, (Versailles, France, Nov), Cambridge University Press, pp Grønbæk, K., Hem, J. A., Madsen, O. L., and Sloth, L Designing Dexter-based Cooperative Hypermedia Systems. Communications of the ACM, 37(2), Grønbæk, K., and Trigg, R. H Design Issues for a Dexter-based Hypermedia System. Communications of the ACM, 37(2), Grønbæk, K., Bouvin, N. O., and Sloth, L Designing Dexter-based Hypermedia s for the World Wide Web. In Proceedings of Hypertext 97, (Southampton, UK, Apr), ACM Press, pp Haake, J. M., Wiil, U. K., and Nürnberg, P. J Having It Both Ways: Combining Open Collaboration and Open Hypermedia s. Paper in progress. 19. Halasz, F., Moran, T., and Trigg, R NoteCards in a Nutshell. In Proceedings of CHI 87, (Toronto, Canada, Apr), ACM Press, pp Hall, W., Davis, H., and Hutchings, G Rethinking Hypermedia - The Microcosm Approach. Kluwer Academic Publishers. 5

6 21. Kacmar, C. J., and Leggett, J. J PROXHY: A Process-oriented Extensible Hypertext Architecture. ACM Transactions on Information Systems, 9(4), Leggett, J. J. and Schnase, J. L Viewing Dexter with Open Eyes. Communications of the ACM, 37(2), Malcolm, K. C., Poltrock, S. E., and Schuler, D Industrial Strength Hypermedia: Requirements for a Large Engineering Enterprise. In Proceedings of Hypertext 91, (San Antonio, Texas, Dec), ACM Press, pp Marshall, C. and Shipman, F Spatial Hypertext: Designing for Change. Communications of the ACM, 38(8), Maurer, H Hyper-G now HyperWave - The Next Generation Web Solution. Addison-Wesley. 26. McCall, R., Bennett, P., D Oronzio, P., Ostwald, J., Shipman, F., and Wallace, N PHIDIAS: Integrating CAD Graphics into Dynamic Hypertext. In Proceedings of ECHT 90, (Versailles, France, Nov), Cambridge University Press, pp Meyrowitz, N The Missing Link: Why We re All Doing Hypertext Wrong. In The Society of Text: Hypertext, Hypermedia, and the Social Construction of Information, MIT Press, Nürnberg, P. J., Leggett, J. J., Schneider, E., and Schnase, J HOSS: A New Paradigm for Computing. In Proceedings of Hypertext 96, (Washington, DC, Mar), ACM Press, pp Nürnberg, P. J., Leggett, J. J., and Schneider, E As We Should Have Thought. In Proceedings of Hypertext 97, (Southampton, UK, Apr), ACM Press, pp Nürnberg, P. J., and Leggett J. J A Vision for Open Hypermedia Systems. Journal of Digital Information, 1(2). 31. Nürnberg, P. J., Leggett, J. J., and Wiil, U. K An Agenda for Open Hypermedia Research. In Proceedings of Hypertext 98, (Pittsburgh, PA, Jun), ACM Press, pp Parunak, H Don't Link Me in: Set based Hypermedia for Taxonomic Reasoning. In Proceedings of Hypertext 91, (San Antonio, TX, Dec), ACM Press, pp Parunak, H Hypercubes grow on Trees (and other Observations from the Land of Hypersets). In Proceedings of Hypertext 93, (Seattle, WA, Nov), ACM Press, pp Pearl, A Sun's Link : A Protocol for Open Linking. In Proceedings of Hypertext 89, (Pittsburgh, PA, Nov), pp Rittberger, M., Hammwöhner, R., Aßfalg, R., and Kuhlen, R A Homogeneous Interaction Platform for Navigation and Search in and from Open Hypertext Systems. In Proceedings of RIAO 94, (New York, NY, Oct. 1994), pp Rizk, A. and Sauter, L Multicard: An Open Hypermedia System. In Proceedings of ECHT 92, (Milan, Italy, Dec), ACM Press, pp Schnase, J. L HB2: A Hyperbase Management System for Open, Distributed Hypermedia System Architectures. Ph.D. Dissertation. Texas A&M University, College Station, Texas. 38. Schnase, J. L., Leggett, J. J., Hicks, D. L., Nürnberg, P. J., and Sánchez, J. A Design and Implementation of the HB1 Hyperbase Management System. Electronic Publishing: Origination, Dissemination and Design, 6(2), Schnase, J. L., Leggett, J. J., Metcalfe, T., Morin, N. R., Cunnius, E. L., Turner, J. S., Furuta, R. K., Ellis, L., Pilant, M. S., Ewing, R. E., Hassan, S. W., and Frisse, M. E The CoLib Project: Enabling Digital Botany for the 21st Century. In Proceedings of Digital Libraries 94, (College Station, TX, Jun), pp Schütt, H. A., and Streitz, N. A Hyperbase: A Hypermedia Engine based on a Relational Database Management System. In Proceedings of ECHT 90, (Versailles, France, Nov), Cambridge University Press, pp Schütt, H. A., and Haake, J. M Server Support for Cooperative Hypermedia Systems. In Proceedings of Hypermedia 93, (Zurich, Switzerland, Mar), Springer Verlag, pp

7 42. Shackelford, D. E., Smith, J. B., and Smith, F. D The Architecture and Implementation of a Distributed Hypermedia Storage System. In Proceedings of Hypertext 93, (Seattle, WA, Nov. 1993), ACM Press, pp Shipman, F., Marshall, C., and Moran, T Finding and Using Implicit Structure in Human-organized Spatial Layouts of Information. In Proceedings of CHI 95, (Denver, CO, May), pp Smith, J. B., and Smith, F. D ABC: A Hypermedia System for Artifact-Based Collaboration. In Proceedings of Hypertext '91, (San Antonio, TX, Dec), ACM Press, pp Streitz, N., Haake, J., Hannemann, J., Lemke, A., Schuler, W., Schütt, H., and Thüring, M SEPIA: A Cooperative Hypermedia Authoring Environment. In Proceedings of ECHT 92, (Milan, Italy, Dec), ACM Press, pp Wiil, U. K Issues in the Design of EHTS: A Multiuser Hypertext System for Collaboration. In Proceedings of HICSS-25, (Kauai, HI, Jan), volume II, IEEE Computer Society Press, pp Wiil, U. K., and Leggett, J. J Hyperform: Using Extensibility to Develop Dynamic, Open and Distributed Hypertext Systems. In Proceedings ECHT 92, (Milan, Italy, Dec), ACM Press, pp Wiil, U. K Experiences with HyperBase: A Multiuser Hypertext Database. SIGMOD RECORD, 22(4), Wiil, U. K., and Østerbye, K. (eds.) Proceedings of the 1st Workshop on Open Hypermedia Systems. Technical Report R , Department of Computer Science, Aalborg University. 50. Wiil, U. K HyperDisco: An Object-Oriented Hypermedia Framework for Flexible Software System Integration. In Proceedings of COMPSAC 95, (Dallas, TX, Aug), IEEE Computer Society Press, pp Wiil, U. K., and Leggett, J. J The HyperDisco Approach to Open Hypermedia Systems. In Proceedings of Hypertext 96, (Washington, DC, Mar), ACM Press, pp Wiil, U. K., and Demeyer, S. (eds.) Proceedings of the 2nd workshop on Open Hypermedia Systems. Technical Report UCI-ICS 96-10, University of California, Irvine. 53. Wiil, U. K., and Leggett, J. J Hyperform: A Hypermedia System Development Environment. ACM Transactions on Information Systems, 15(1), Wiil, U. K., and Leggett, J. J Workspaces: The HyperDisco Approach to Internet Distribution. In Proceedings of Hypertext 97, (Southampton, UK, Apr), ACM Press, pp Wiil, U. K. (ed.) Proceedings of the 3rd Workshop on Open Hypermedia Systems. Scientific Report 97-01, The Danish National Centre for IT Research. 56. Wiil, U. K. (ed.) Proceedings of the 4th Workshop on Open Hypermedia Systems. Technical Report CS-98-01, Aalborg University Esbjerg. 57. Wiil, U. K., and Nürnberg, P. J Evolving Hypermedia Middleware s: Lessons and Observations. In Proceedings of SAC 99, (San Antonio, TX, Feb), ACM Press. 58. Østerbye, K., and Nørmark, K An Interaction Engine for Rich Hypertexts. In Proceedings of ECHT 94, (Edinburgh, Scotland, Sep), ACM Press, pp