This book constitutes the thoroughly refereed post-conference proceedings of the 5th International Workshop on Semantics in Data and Knowledge Bases, SDKB 2011, held in July 2011 in Zürich, Switzerland. The 8 revised full papers presented were carefully selected from numerous submissions covering topics of formal models for data and knowledge bases, integrity constraints maintenance and dependency theory, formal methods for data and knowledge base design, reasoning about data and knowledge base dynamics, adaptivity for personalised data and knowledge bases view-centered data- and knowledge-intensive systems, information integration in data and knowledge bases, knowledge discovery in data and knowledge bases, validation and verification of data and knowledge base designs, formal linguistics for data and knowledge bases, logical and mathematical foundations of semantics, semantics in data- and knowledge-intensive applications.