Algorithms for parsing search queries in systems with inverted file organization

In an inverted file system a query is in the form of a Boolean expression of index terms. In response to a query the system accesses the inverted lists corresponding to the index terms, merges them, and selects from the merged list those records that satisfy the search logic. Considered in this paper is the problem of determining a Boolean expression which leads to the minimum total merge time among all Boolean expressions that are equivalent to the expression given in the query. This problem is the same as finding an optimal merge tree among all trees that realize the truth function determined by the Boolean expression in the query. Several algorithms are described which generate optimal merge trees when the sizes of overlaps between different lists are small compared with the length of the lists.