Abstract
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.
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