Introduction

Since the early 1990s, with the rapid development of information and communications technology (ICT) and global attention to the conservation and preservation of cultural heritage, thousands of varieties of digital libraries (DLs) have been created all over the world for different applications. They are increasing in number and evolving in nature. Much effort has been made in the design and implementation of DLs, but their evaluation has not received as much attention in research and practice. Evaluation should be an integral part of the research and development (R&D) process. Although it has been seldom addressed in the literature, much work has been done, focusing on system-centred or objective evaluation. User-centred or subjective evaluation, using different approaches and methodologies, has increasingly attracted attention (Saracevic, 2004; Borgman, 2003; Marchionini et al., 2003). Nevertheless, DL evaluation is facing a conceptual and pragmatic challenge (Saracevic, 2000, 2004). For the conceptual challenge, a theoretical basis for evaluation is urgently needed.

The major purpose of this paper is to propose a multidimensional and multilevel integrated theoretical framework of DL success from the users’ perspective. Based on the components and nature of DLs, the challenges of evaluation and the problems of existing assessment frameworks, the proposed framework mainly adopts DeLone and McLean's (2003) Model of Information System Success (D&M Model) as a theoretical base, with refinement for answering the questions: How do users evaluate DL success? How do individual differences and DL contexts influence users’ assessment of DL success?

The components and nature of digital libraries

Scholars define a DL in different ways, but no matter how it is defined and evolves, a DL is an information system by nature. Borgman et al. (1996) and Borgman's (2000, 2003) two-part definition gives more insights into the components and nature of a DL. The first part of the definition emphasizes using information technology to organize electronic resources ‘for creating, searching, and using information’ (Borgman, 2000, 42). The second stresses the provision of user-centred services that are extended from physical to digital contexts. Through the information system (IS), users interact virtually with the DL to use services and to share ideas with other users. The two-part definition of a DL is not separated but inter-related, and it should be integrated as a whole both in research and in practice.