Incremental Encoding of Multiple Inheritance Hierarchies

摘要

Incremental updates to multiple inheritance hierarchies are becoming more prevalent with the increasing number of persistent applications supporting complex objects, making the efficient computation of lattice operations such as greatest lower bound (GLB), least upper bound (LUB), and subsumption more and more important. General techniques for the compact encoding of a hierarchy are presented. One such method is to plunge the given ordering into a boolean lattice of binary words, leading to an almost constant-time complexity of the lattice operations. The method is based on an inverted version of the encoding of Ait-Kaci et al. to allow incremental update. Simple grouping is used to reduce the code space while keeping the lattice operations efficient. Comparisons are made to an incremental version of the range compression scheme of Agrawal et al., where each class is assigned an interval, and relationships are based on containment in the interval. The result is two encoding methods which have their relative merits. The former being better for smaller, more structured hierarchies, and the latter for larger, less organized hierarchies.