On the Index Selection Problem applied to Key oriented XML Indexes

In the world of Relational Database Management Systems (RDBMS) indexes are used to accelerate specific queries. The selection of indexes is an important task in database-tuning which is performed by a database administrator or an index selection tool which suggests a set of suitable indexes. In this paper we transfer the concept of specific indexes to XML Database Management Systems (XDBMS) and present an implementation that uses occurring queries to optimize the performance of an XML database system by automatically creating suitable indexes . We introduce an index approach, called key oriented XML index, that uses specific XML element values and attribute values as keys referencing arbitrary nodes in the data. We transfer the wellknown Index Selection Problem (ISP) to XDBMS. Solving the ISP, a workload of database operations is analyzed and a set of specific indexes that minimizes the total execution time is suggested. Because the ISP is an NP complete problem, we apply heuristics to find a solution with reduced complexity. Experimental results of the prototypical implementation of the key oriented XML indexes on top of a native XDBMS demonstrate that our approach significantly improves the query execution time with only moderate additional storage requirements. Because the workload is analyzed periodically and suitable indexes are created or dropped automatically by solving the ISP, our approach guarantees high performance over the total life time of a database.