An incremental algorithm for computing ranked full disjunctions
Sara Cohen, Yehoshua Sagiv · 2005
The full disjunction is a variation of the join operator that maximally combines tuples from connected relations, while preserving all information in the relations. The full disjunction can be seen as a natural extension of the binary outerjoin operator to an arbitrary number of relations and is a useful operator for information integration. This paper presents the algorithm INCREMENTALFD for computing the full disjunction of a set of relations. INCREMENTALFD improves upon previous algorithms for computing the full disjunction in three ways. First, it has a lower total run-time when computing the full result and a lower runtime when computing only k tuples of the result, for any constant k. Second, for a natural class of ranking functions, INCREMENTALFD returns tuples in ranking order. Third, INCREMENTALFD can be adapted to have a block-based execution, instead of a tuple-based execution.