Database Searching and Strategies (HC): Companions, Handbooks, and Guides

These kinds of reference books provide overviews that address major issues and topics within a field of study.  The authors not only discuss key content but they also provide a more sophisticated level of analysis and contextualization than you might find in a textbook or introductory study.  The authors are chosen for their research in specific areas and deliver authoritative essays.  The material they choose to include in their bibliographies are good points of departure for further research and reading.