This book presents a collection of coordinated scientific papers describing the work conducted and the results achieved within the LOGIDATA+ project, a research action funded by the Italian national research council CNR. Theaim of the LOGIDATA+ project is the definition of advanced database systems which significantly extend the functionalities of the current systems, with specific reference to the application areas for which relational systemsare not considered satisfactory. These new systems will allow the definitionof data with complex structures, the representation of semantic relationships between objects, and the use of powerful query and update languages. They will be based on a combination of techniques originatingfrom relational databases and logic programming, with contributions from object-oriented programming. The goal of the LOGIDATA+ project is the design, definition, and prototype implementation of a database management system with complex structures and a class hierarchy, to be accessed through a rule-based language. This book presents an integrated view of the project at the end of the first phase. The second phase will be mainly concerned with the implementation of prototypes.