Challenges for digital library evaluation

While there were many efforts in research and practice of digital libraries, evaluation was not a conspicuous activity. It is well recognized that digital library evaluation is a complex and difficult undertaking. We enumerate the challenges facing digital library evaluation and suggest a conceptual framework for evaluation. A review of evaluation efforts in research and practice concentrates on derivation of criteria used in evaluation. Essential requirements for evaluation are stated. Discussed are constructs, context and criteria of digital libraries: What should we evaluate? For what purpose do we evaluate? At what level do we evaluate? Upon what criteria do we evaluate? In addition we include suggestions for adaptation of criteria from related activities. The paper is considered as a part of the evolution of concepts for digital library evaluation.