The ACM PODS Alberto O. Mendelzon test-of-time award 2012

In 2007, the PODS Executive Committee decided to establish a Test-of-Time Award, named after the late Alberto O. Mendelzon, in recognition of his scientific legacy, and his service and dedication to the database community. Mendelzon was an international leader in database theory, whose pioneering and fundamental work has inspired and influenced both database theoreticians and practitioners, and continues to be applied in a variety of advanced settings. He served the database community in many ways; in particular, he served as the General Chair of the PODS conference, and was instrumental in bringing together the PODS and SIGMOD conferences. He also was an outstanding educator, who guided the research of numerous doctoral students and postdoctoral fellows. The Award is to be awarded each year to a paper or a small number of papers published in the PODS proceedings ten years prior, that had the most impact (in terms of research, methodology, or transfer to practice) over the intervening decade. The decision was approved by SIGMOD and the ACM. The funds for the Award were contributed by IBM Toronto. The paper deals with a central problem in database research, namely finding classes of conjunctive queries for which problems, such as the evaluation of Boolean queries and query containment, are in polynomial time. This problem has attracted a lot of attention since the pioneering work of Yanakakis on acyclic queries. The paper shows that the earlier notion of bounded query width (introduced by Chekuri and Rajaraman in ICDT 97) is NP-hard, introduces the notion of bounded hypertree width, then shows that this notion properly generalizes earlier notions of acyclicity, that constant hypertree width is efficiently recognizable, and that Boolean queries with constant hypertree width can be efficiently evaluated. The results of the paper are applicable to both conjunctive query evaluation and to constraint satisfaction. The paper is extensively cited in the literature, and had an impact on subsequent research on these two problems. Hence, the committee has found it to be worthy of the Award.