Most current hypertext systems are basically closed systems. That is, material created in one system cannot be easily integrated with material created in another system. An open hypermedia system is a system which can connect to other information systems (both hypertext and non-hypertext). It should be able to freely exchange data. Distribution allows the system to store at geographically dispersed sites in a manner transparent to the user.
Future generation hypermedia systems must provide adequate support for collaborative work. This includes simultaneous multi-user access to the hypermedia network, robust concurrency control mechanisms, broadcasting to users any changes made to the network by other users, and tracking contributions made by each member of a team.
The database layer should preserve data integrity and provide traditional secondary storage management and data administration facilities. It should forbid dangling references to objects or attributes and prevent recursive inclusion of composite objects [Schutt & Streitz, 1990]. It should also support either the notion of rules as in extended relational databases or the concept of semantics as in object-oriented databases.
Most current generation hypermedia systems deal with static information. Future systems need the ability to dynamically reconfigure the network in response to changes made to the network or its contents. Virtual or dynamic structures (active objects) are similar to dynamically generated views in relational databases. Virtual structures are possible only when current models are changed to adapt to changing information.
In addition to navigational access to information, hypermedia systems should provide efficient search and query mechanisms. This would partly solve the "lost in space" (disorientation) problem experienced by users during navigation. There can be two kinds of queries - a structure query to retrieve a part of the network and a content query to retrieve a specific node. The former requires the development of a query language geared towards dealing with hypertext network structures.
The integration of AI into hypermedia engines will be an interesting area to explore. This would include inheritance, truth maintenance, rule based searching, and inference engines. Computation built into the hypermedia system is likely to be more efficient for extensive access to information in the network.
With increasing use of hypermedia for sophisticated applications it becomes necessary to deal with groups of nodes and links. This will require making a composite node as a primitive construct in the basic hypermedia model. Inclusion (or part-of) relations have to be supported in addition to standard, referential links.
Versioning is required in order to keep track of changes to the network. This can include versioning at the level of individual entities such as nodes and links and also at the level of the hypermedia network as a whole.
The database layer should be able to efficiently store and retrieve multiple media. It should also provide transparent access to different storage media.
Extensibility involves the ability to handle extensions to the existing data model (schema evolution) in a flexible and safe manner. The database layer should not only be able to handle the structural part of the hypertext data model but also the semantic part to ensure data abstraction and encapsulation of the evolving data model.