Selection predicate indexing for active databases using interval skip lists

A new, efficient selection predicate indexing scheme for active database systems is introduced. The selection predicate index proposed uses an interval index on an attribute of a relation or object collection when one or more rule condition clauses are defined on that attribute. The selection predicate index uses a new type of interval index called the interval skip list (IS-list). The IS-list is designed to allow efficient retrieval of all intervals that overlap a point, while allowing dynamic insertion and deletion of intervals. IS-list algorithms are described in detail. The IS-list allows efficient on-line searches, insertions, and deletions, yet is much simpler to implement than other comparable interval index data structures such as the priority search tree and balanced interval binary search tree (IBS-tree). IS-lists require only one third as much code to implement as balanced IBS-trees. The combination of simplicity, performance, and dynamic updateability of the IS-list is unmatched by any other interval index data structure. This makes the IS-list a good interval index structure for implementation in an active database predicate index. ‡ ‡ The C++ source code for interval skip lists can be obtained at http://www.cis.ufl.edu/~hanson/IS-lists/ or by sending a request by e-mail.