RCdex: An Index Structure for Tree Matching in the Presence of Commutations

Tree-structured data models and formats are increasingly being used in many applications to represent and store data objects. Since the structural information inherent in such data cannot be captured in conventional index structures, quick retrieval of tree-structured data necessitates special indexing techniques. A variety of algorithms, such as ViST and Data Guides, have been proposed to answer tree queries efficiently. Nonetheless, a class of tree-structured data, which are insensitive to certain commutations between the elements, cannot be indexed using the existing techniques. In this paper, we propose an index structure (RCdex) to efficiently answer wildcard (“ ”) queries in the presence of commutations. We experimentally show that this approach provides large savings in query execution time when commutations between the nodes of the tree are allowed.