A multiple-depth structural index for branching query

XML structural index, which acts as a schema, plays an important role in XML query optimization and formulation. To provide a reasonable structural index for branching path query under space constraint, we propose an adaptive index of multiple local branching depths and multiple local bisimilarities, which is constructed by maximizing marginal gain for given query load. It cannot only give good support to branching path queries but also have much smaller size compared with that of same sort of index. Detailed experiments have shown that the index is effective and efficient for XML branching path query.