This book presents a collection of coordinated scientificpapers describing the work conducted and the resultsachieved within the LOGIDATA+ project, a research actionfunded by the Italian national research council CNR. Theaim of the LOGIDATA+ project is the definition ofadvanced database systems which significantly extend thefunctionalities of the current systems, with specificreference to the application areas for which relationalsystemsare not considered satisfactory. These new systemswill allow the definitionof data with complex structures,the representation of semantic relationships betweenobjects, and the use of powerful query and update languages. They will be based on a combination of techniquesoriginatingfrom 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 systemwith complex structures and a class hierarchy, to beaccessed through a rule-based language. This book presentsan integrated view of the project at the end of the firstphase. The second phase will be mainly concerned with theimplementation of prototypes.