Dale, Jonathan

DeRoure, David C.

Goose, Stuart

Hall, Wendy

English

Southampton (e-Prints Soton)

UNIVERSITY OF SOUTHAMPTONDEPARTMENT OF ELECTRONICS AND COMPUTER SCIENCEMICROCOSM TNG: A DISTRIBUTEDARCHITECTURE TO SUPPORT REFLEXIVEHYPERMEDIA APPLICATIONSStuart Goose, Jonathan Dale,Wendy Hall and David C. DeRoureUniversity of SouthamptonFebruary 1997Presented at HT’972An example of this abstract model in context is given in figure 1. Encyclopaedia is a session that iscomprised of many applications which describe its behaviour, both in terms of information content andfunctionality. Such a session is a dynamically extensible entity within which new applications can beplugged or unplugged at any time. As the session is not monolithic or statically defined, alternativeviews can be generated simply by including or excluding various application sub-hierarchies. Forexample, a Junior Encyclopaedia may use some of the same applications as Encyclopaedia, but notincorporate others deemed unsuitable for younger audiences.The reflexive model provides a flexible and extensible approach that allows a user to author multipleand different views on the same set of applications, depending upon the context of the structure inwhich they are placed. Moreover, these contextual applications can be shared across a number of users,promoting information dissemination and raising the level at which hypermedia resources may bereused.4. Mapping the Model to a Distributed FrameworkIn moving from the abstract to the physical, we have built a prototype system, called Microcosm TNG[3] which retains the core philosophies of Microcosm.The prototype has three distinct layers. The Presentation Layer is responsible for rendering themultimedia information on the screen. The Link Service Layer comprises an arbitrary number ofprocesses, originally known as filters in Microcosm terminology, which exist to serve any request fromthe user. Traditional services such as link authoring, link resolution, link navigation and informationretrieval searches can be provided at this layer. The above two layers rely heavily upon communicationto fulfil their roles, and as such the third layer, the Communication Layer, offers facilities for messageScientific Medical LanguageEnglish French Computing Engineering MathematicalCivilEngineeringElectricalEngineeringEncyclopaediaSessionFigure 1 : An Example Session and Application StructureDomain 2DaemonStuart’s Session"Lions"ApplicationLinkbase RouterLinkerAvailLinksDocu-verseDomain 1DaemonJonathan’s Session"Tigers"ApplicationRouterLinkerAvailLinksDocu-verseLinkbaseViewer"Cats"Appli-cationDocu-verseLinkbaseProcessManagerProcessManagerFigure 2 : Application Sharing in Microcosm TNG3passing and process management.From figure 2 it can be appreciated how Microcosm TNG is modelled as discrete processes within theframework. The user Jonathan in domain 1 has several processes running within his session, as doesuser Stuart in domain 2. The dotted lines denote a collection of processes which have been published asapplications. Jonathan has published an application named Tigers and Stuart can use the Tigersapplication together with his Lions application to enrich his more general application regarding Cats.Although the framework provides a peer process model, the reflexive model allows the user to composecollections of processes dynamically into coherent and logically related hierarchies. These, in turn, canbe published for others to use. The reflexive property of applications is modelled in the frameworkthrough the passing of messages. When a user issues a service request to a particular application therequest is transparently propagated down through the application hierarchy.5. ConclusionsThe authors introduced the definition of a hypermedia application and explained how it provides acontainer for encapsulating a group of processes with their respective resources. This provides a usefuldegree of abstraction allowing them to be considered as self-contained, publishable and shareableentities. The application conceals configuration details and provides a mechanism for building andcomposing new applications. By extending the definition of an application to include one or moreapplications, the model can exhibit the property of reflexivity. This allows users to construct richhierarchies of reusable applications.Microcosm TNG is an open distributed hypermedia system that combines the distributed informationsharing offered by most systems; distributed information organisation, as offered by Hyper-G anddistributed services, as offered by Microcosm. Microcosm TNG is a widely distributed, heterogeneous,multi-user systems that provides a framework in which reflexive applications can reside.References[1] ANDREWS, K., KAPPE, F. and MAURER, H., Serving Information to the Web with Hyper-G. In:Computer Networks and ISDN Systems, 27(6), pages 919-926, 1995.[2] FOUNTAIN, A., HALL, W., HEATH, I. and DAVIS, H. C., Microcosm: An Open Model forHypermedia With Dynamic Linking. In: Proceedings of the Hypertext ’90 Conference, INRIA,France, pages 298-311, 1990.[3] GOOSE, S., DALE, J., HILL, G. J., DeROURE, D. C. and HALL, W., An Open Framework forIntegrating Widely Distributed Hypermedia Resources. In: Proceedings of the IEEE InternationalConference on Multimedia Computing and Systems, Hiroshima, Japan, pages 364-371, June, 1996.[4] HILL, G. J. and HALL, W., Extending the Microcosm Model to a Distributed Environment. In:Proceedings of the Hypertext ’94 Conference, Edinburgh, Scotland, pages 32-40, September, 1994.

An Open Framework for Integrating Widely Distributed Hypermedia Resources. In:

Extending the Microcosm Model to a Distributed Environment. In:

Microcosm: An Open Model for Hypermedia With Dynamic Linking. In:

Serving Information to the Web with Hyper-G. In:

Microcosm TNG: A Distributed Architecture to Support Reflexive Hypermedia Applications

Microcosm TNG: A Distributed Architecture to Support Reflexive Hypermedia Applications

Abstract

Similar works

Full text

Available Versions

Southampton (e-Prints Soton)