Workload-aware Trie Indexes for XML

Well-designed indexes can dramatically improve query performance. In the context of XML, structural indexes have proven to be particularly effective in supporting efficient XPath queries the core of all XML queries, by capturing the structural correlation between data components in an XML document. The duality of space and performance is an inevitable trade-off at the core of index design. It has been established that query workload can be leveraged to balance this trade-off and maximize the throughput of a group of queries. In this paper, we propose a family of novel workload-aware indexes by taking advantage of the recently proposed Trie indexes for XML. In particular, we propose the WP [k]-Trie, the AWP [k]-Trie, and the W[k ]Trie indexes, which use the P [k]-Trie framework to index frequent label-paths and a carefully selected complimentary set of label-paths. When a WP [k]-Trie index is available, all frequent path queries are guaranteed to be evaluated in one index lookup, and all core XPath queries are guaranteed to be evaluated with index-only plans. With further consideration of the representativeness of label-paths in the index and proper annotations, the AWP [k] and W[k ]-Trie indexes are able to improve query evaluation performance by efficiently singling out queries with empty results and enabling more efficient query decompositions, with the W[k ]-Trie minimizing the space requirements of the index.