Doctoral theses at NTNU, 2006:190 Printed by NTNU-trykk To MY LOVING WIFE YUN LIN

iii Advances in peer-to-peer overlay networks and Semantic Web technology will have a substantial influence on the design and implementation of future digital libraries. However, it remains unclear how best to combine their advantages in constructing digital library systems. This thesis is devoted for investigating, proposing and evaluating possible solutions to advance developments in this field. The main research goal of this work is to combine the strengths of both peer-to-peer overlay networks and Semantic Web for facilitating semantic searches in large-scale distributed digital library systems. The approach has been conducted in a sequential and progressive manner. Firstly, we recognize system infrastructure and metadata heterogeneity as two major challenges in conducting semantic searching across distributed digital libraries. Next, we investigate the strengths and weaknesses of both peerto-pee