Hybrid Library Architecture and Hybrid Library Management System
The diagram shows the logical structure for the hybrid library management structure. It shows three distinct classes of component:
User access points - typically web browsers whereby users gain access to the underlying system. It is likely that the Hybrid Library user access system will make use of JAVA to enable more real-time user-interaction than is possible with basic 'single-shot' HTML based interfaces.
'Hybrid Library Management System' - this is the kernel of the hybrid library system. It is this component that provides a consistent and contextualised view of the user's 'information landscape' and dynamically maps users' service requests onto the various underlying atomic library components. In some instances where the institution does not have a local version of a service the kernel may provide that service itself as a proxy. For example the kernel may include web indexing and ILDRMS facilities that may be used in the absence of locally preferred alternatives. The layers of this component are described more fully below.
Hybrid library components - the existing, currently disintegrated components that make up the hybrid library environment. In addition to traditional library facilities such as the local catalogue and networked CDs etc., the Agora project proposes to integrate access to more innovative components such as Web Indexes, Clumps, electronic document delivery systems etc. thus providing a more holistic view of the library service.
The Hybrid Library Management System Kernel
User Services Access Layer
The user services access layer is responsible for providing the userís view of the hybrid library. This consists of the following major system areas:
Web gateway ñ clearly the primary user access mechanism to the hybrid library will be through a web browser. The web gateway enables such access ñ it should be noted that this would involve some use of JAVA applets in order to achieve the level of real-time responsiveness required.
Open Authentication Service ña strong distributed authentication service is outside the scope of this project, however some form of authentication is essential within the HLMS and this must be developed in a way that allows easy migration to future mechanisms as they are deployed. Within the Agora project the HLMS will provide an optional ëconvenience basedí authentication service. If an authentication challenge is issued by a library component, the HLMS server will attempt to resolve the challenge on behalf of the user using forward knowledge. For example the HLMS server may know account details for the challenging server, if no such information is known the challenge will be passed up to the user. The interface to the authentication service will be developed to allow adoption of more sophisticated schemes as they are deployed.
Information Landscape Definition ñ providing the user view of services.
Open Standard Service Description Layer
Of fundamental importance to hybrid library services and distributed library services is that the features and facilities of the underlying atomic services represented are described to the upper layers. It is inconceivable, and highly undesirable, that all the underlying components will become homogeneous in the services that they offer. Hence a layer is required that can describe these services to the user access components to allow dynamic configuration to avoid users requesting services that are unavailable or for available services not to represented on the interface. For future scaling of the system it is essential that this service definition be performed in an open and standard manner. The Agora project will use the explain service as defined within Z39.50 to provide a service description ñ this facility describes databases in terms of: schema; access points; usage costs; record syntax; services provided (e.g. search, request, delivery etc.); content. It should be noted that the database content description within Z39.50 is fairly weak and therefore integration of ëCentroidsí technology will be investigated in order to gain richer information concerning database content. In the ideal world all components within the hybrid library environment would be ëself-describingí ñ whilst this is possible within the proposed architecture (the components should provide explain interfaces), it is highly unlikely that any of the underlying components would provide such an interface within the time scale of the project. The service description layer will also contain an explain proxy database which allows services descriptions to be stored within the HLMS server. In this way the proposed architecture provides rich interoperability in todayís systems environments whilst providing a platform for future more scaleable inter-operability scenarios.
Hybrid Service Access & Proxies Layer
This layer provides open interfaces to hybrid library components, particularly through Z39.50 and ISO ILL protocol gateways. However, because some of the implementations of hybrid library components available currently will not support such open interfaces, this layer will also provide local versions of some services. The hybrid services access & proxies layer will include:
Parallel Z39.50 client ñ for transparently querying multiple Z39.50 targets (e.g.. local catalogues, remote catalogues / clumps, CDs, Web indexes etc.).
ISO ILL Document Requesting & Electronic Delivery gateway ñ for integrating with local ILDRMS facilities or as an adjunct.
Web crawler & Index ñ a web crawler to populate an index with meta-data (including Dublin Core) that is available as a Z39.50 server.
Alerting and current awareness agent ñ current awareness services can be generated from any of the underlying data sources. This service will scan the underlying databases for new information matching user profiles.