Figure 1: The Microcosm Model
- Specific Links
- The user is able to follow the link only after selecting the anchor at a specific location in the current document. Specific links may be made into buttons.
- Local Links
- The user is able to follow the link after selecting the given anchor at any point in the current document.
- Generic Links
- The user is able to follow the link after selecting the given anchor at any point in any document. Generic links are of considerable benefit to the author in that a new document may be created and immediately have access to all the generic links that have previously been defined.
- Dynamic Links
- Not all links need to be created by an author. For example, relationships between pieces of information can be computed, based on statistical analysis of the content (e.g. Computed Links), or related information can be retrieved based on attribute coding of documents.
- Viewers
- Programs which allow the user to view a document in its native format. The task of the viewer is to allow the user to peruse the document, to make selections and to choose actions. Typical actions are follow link, start link and end link (where links may be to processes as well as to documents). The actions themselves are not effected by the viewer. The viewer is responsible for binding the information into a message, which is sent on to the filter chain where it will look for one or more processes that can satisfy this request.
- Filters
- Processes which are responsible for receiving messages, taking any appropriate actions, and then handing the message on to the next filter in the chain. The actions that filters take are such as changing a message, or adding or removing messages.
2. External Application Integration With Microcosm
It has always been a goal of the hypermedia community to provide information management systems which are not restricted to their own private data sets but which can encompass any and all of the information a person may wish to access when carrying out some task. The Microcosm system, with its loosely coupled process model provides a suitable framework within which external applications can be integrated. It also provides a unique plug-and-play environment, where new functionality can be easily added into system by adding new processes. Also, the selection/action model provides a simple gateway to system functionality. Finally, a simple, unstructured, ASCII-based message format allows the widest possible range of applications to interpret and generate messages for the system.It is worth looking at two ways in which Microcosm and an external application might be coupled together.
- Through extending an existing application to provide hypermedia functionality (i.e. as a viewer)
- Through extending the functionality within the hypermedia system by introducing a new external information system (i.e. as a filter).
3. Extending an External Application
The Microcosm system provides a very simple model for all applications that require hypermedia functionality. As was described above, a viewer is responsible for displaying and allowing the user to interact with information, and then generate requests to the hypermedia system based on that interaction. This may be explicit (for example, the user has asked to find any links which are bound to "horse" at this location in this document) or implicit (for example, the system has just opened this document, tell me where any buttons are located). In either case, the method for initiating these tasks is the same, by constructing and sending a Microcosm message.This provides a very simple method for invoking these same hypermedia functions from an external application. Provided there is some method by which information about the document can be extracted from the application (for example, the current selection, the location, the name of the document being displayed), exactly the same interactions with the hypermedia system can take place as above.
How easily an application is integrated, and how much effort will be required to achieve that integration can be calculated by considering the following items :-
- The level to which the application can be externally programmed.
The more configurable an application is, the easier it is to integrate,
especially if it supports scripting languages or some sort of run-time
extensions. [Davis94] is one such tool, which can provide integration across
a vast spectrum of external applications.
4. Extending the functionality of the Hypermedia System
For hypermedia systems to gain commonplace acceptance, they need to be able to draw from a wide range of resources, not necessarily static in nature. Currently, however, these hypermedia systems are considered to be separate from other information systems (for example, spreadsheets, databases, rule-bases, etc.).In the Microcosm system, a filter can be considered analogous to an information system. It receives messages from other processes, makes some decision based upon that message and may, as a result, generate new messages for other filters. Protocols exist within Microcosm to govern the way in which processes interact to perform specific tasks (for example, link generation, retrieval, navigation or display). Any new information system that wishes to enrich the Microcosm environment can do so by participating in these protocols.
The selection/action model used for initiating a task within Microcosm means one process does not have to be specifically aware of the existence or particular implementation of another process which will participate in the task (unless, of course, the process requires this ability). However, the system is not limited to just these protocols. It is possible to extend the set of possible tasks and thus protocols understood by the system at any time. If a particular application requires additional functionality, this can be added by implementing a new filter that can then be plugged straight into the system, even while it is running.
Because of this approach, the problem of integrating external information systems is reduced (again) to that of understanding the messages Microcosm uses and interacting with any protocols which are appropriate. In one example, a Prolog rule-base was integrated with Microcosm to provide a simple expert system for the location of faults in a factory environment [Heath94]. Here, an interface layer (or shim) was written to allow the Prolog rule-base to become a part of the Microcosm environment. Also, a private protocol was designed so that a separate form-based user interface could both query the rule-base and access the rich link structure already available within this application.
This is not to say that it is a trivial task to integrate any information system. The information system needs to be more closely integrated with the hypermedia system as it has to actively participate in the protocols it has to deal with, and can not simply "fire-and-forget" messages as can the external application described in section 2. Because of this active participation, any interface layer (shim) has to be tightly coupled to the particular information system, making the building of generic tools a more difficult proposition.
5. Conclusions
The Microcosm model, often described as a link service, provides external applications with access to hypermedia functionality for minimal effort. The degree to which this functionality can be integrated with the application is only dependent on the flexibility of the application itself. The message passing and protocols makes the system easy to extend and to drive externally. It is possible to develop new protocols in order to add new features that the system doesn't support. By exploiting operating system features, Microcosm can "play tricks" to integrate the vast majority of applications through tools such as the Universal Viewer. However, there is still a degree of user intervention required before an external application and Microcosm can co-operate.However, for hypermedia systems to be fully able to interact with other applications in a particular working environment requires support for inter-application co-operation at the operating system level. This is starting to happen, as manufacturers embrace the open standards being developed for the various environments (AppleEvents on the Macintosh, OLE Automation for Windows). This also requires application developers to make use of these features so generic integration tools can be built. However, this is still new technology and as such will only be embraced by the current state-of-the-art application builders. There are still a large number of legacy systems being used which will still have to be dealt with, probably by employing some of the methods described above.
6. References
[Davis92] Davis, H.C., Hall, W., Heath, I., Hill, G.J. & Wilkins, R.J. Towards an Integrated Environment with Open Hypermedia Systems. Proceedings of the ACM Conference on Hypertext, ECHT'92, Milan, Italy, December 1992, pp 181-190. ACM Press 1992.[Davis94] Davis, H.C., Knight S. & Hall, W. Light Hypermedia Link Services: A Study of Third Party Application Integration. Proceedings of the ACM European Conference on Hypermedia Technology, ECHT'94, Edinburgh, Scotland, September 18-23, 1994, pp 41-50
[Fountain90] Fountain, A.M., Hall, W., Heath, I. & Davis, H.C. MICROCOSM: An Open Model for Hypermedia with Dynamic Linking, in A. Rizk, N. Streitz & J. Andre eds. Hypertext: Concepts, Systems and Applications. The Proceedings of the European Conference on Hypertext, INRIA, France, pp 298-311 Cambridge University Press. 1990
[Heath94] Heath, I., Hall, W., Crowder, R.M., Pasha, M.A. & Soper P.J. Integrating a Knowledge Base with an open Hypermedia System and its application in an Industrial Environment, Proceedings for 3rd International Conference on Information and Knowledge Management CIKM'94 Workshop on Intelligent Hypertext Nov 29 - Dec 1, 1994, NIST Gaithersburg, Maryland.