Supporting Relationships in Digital Libraries
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The motivation for this work is based on two recognized research issues for digital libraries. One is the need for interlinked and semantically rich information spaces where relationship information is of particular importance. The other is the serviceoriented architecture of digital libraries. The digital libraries of the future will consist of smaller and independent systems that each will provide different functionality and access to different contents. This work defines and explores a service for managing and using explicit relationships – the Digital Library Link Service. The service implements an instance-oriented approach to relationships that enables any kind of typed relationship to be created among the information objects of digital libraries. The service can be used to create consistent information spaces on top of digital library repositories and enables an associative organization and retrieval of information objects. This work shows that the use of a fine-grained relationship model implemented as distributed objects enables distribution of the relationship network while still being able to support constraints and maintain consistency. The cost of this, however, is a complexity that can reduce performance and scalability due to the call latency of network communication. A prototype is developed that utilizes caching in order to solve this. Tests conducted show that this technique significantly contributes to the scalability and efficiency. This is particularly important when the relationship information is distributed across different processes with high calllatency in between. The work further presents a prototype application for enhancing bibliographic catalogues with the rich set of relationship types defined in the bibliographic information model proposed by the International Federation of Library Associations and Institutions – the FRBR model. The Digital Library Link Service is used to implement an index that facilitates the navigation of bibliographic relationships in order to explore bibliographic entities along the paths laid out by the FRBR model. This demonstrates the applicability of the service as a flexible tool for associative organization of information objects. The main applications of the service are limited to systems with a relaxed requirement in terms of automatic processing of larger sets of relationships. The main access paradigm explored for interacting with relationships is by navigation. The need for automatic and efficient processing of a large relationship network, e.g. for the purpose of indexing, can be supported by extending the system with additional functionality. Another recognized problem is that the use of CORBA references to address long-term persistent information can cause referential integrity problems. One possible way to solve this is to assigning objects globally unique identifiers that later can be used to recover from referential integrity problems.