This volume contains the articles presented at the 6th International Symposium on Foundationsof Informationand KnowledgeSystems (FoIKS 2010)which was held in So?a, Bulgaria during February 15-19, 2010. The FoIKS symposia provide a biennial forum for presenting and discussing theoreticalandappliedresearchoninformationandknowledgesystems.Thegoal is to bring together researchers with an interest in this subject, share research experiences, promote collaboration and identify new issues and directions for future research. FoIKS 2010 solicited original contributions dealing with any foundational aspects of information and knowledge systems. This included submissions that apply ideas, theories or methods from speci?c disciplines to information and knowledge systems. Examples of such disciplines are discrete mathematics, logic and algebra, model theory, information theory, complexity theory, algorithmics and computation, statistics, and optimization. Previous FoIKS symposia were held in Pisa (Italy) in 2008, Budapest (Hungary) in 2006, Vienna (Austria) in 2004, Schloss Salzau near Kiel (Germany) in 2002, and Burg/Spreewaldnear Berlin (Germany) in 2000.FoIKS took up the tradition of the conference series Mathematical Fundamentals of Database Systems (MFDBS), which initiated East-West collaboration in the ?eld of database theory. Former MFDBS conferences were held in Rostock (Germany) in 1991, Visegrad (Hungary) in 1989, and Dresden (Germany) in 1987. The FoIKS symposia are a forum for intense discussions. Speakers are given su?cient time to present their ideas and results within the larger context of their research. Furthermore, participants are asked in advance to prepare a ?rst response to a contribution of another author.