This special issue contains six selected journal papers originally presented at the International Conference on Database Theory (ICDT 2011), which was held jointly with the International Conference on Extending Database Technology (EDBT 2011) on 21–25 March 2011 in Uppsala, Sweden.

ICDT is one of the major forums for the presentation of research on all aspects of theoretical aspects within databases. Six of the twenty-two papers presented at the conference were invited to submit an extended journal version to this special issue. The paper “Querying Probabilistic Business Processes for Sub-Flows,” by Daniel Deutch, was also selected for the ICDT Best Student Papers Award.

The submissions for the special issue underwent a new and thorough journal reviewing and revision process, in accordance with the usual standards of Theory of Computing Systems. We thank the authors and the reviewers for all their hard work producing the contents of this issue.

Guest Editor