Medical informatics researchers have explored a number of ways to integrate medical information resources into patient care systems. Particular attention has been given to the integration of on-line bibliographic resources. This paper presents an information model which breaks down the integration task into three components, each of which answers a question: what is the user's question?, where can the answer be found?, and how is the retrieval strategy composed? Twelve experimental systems are reviewed and their methods for addressing one or more of these questions are described.