uments Graphs

The increasing popularity of XML has generated a lot of interest in query processing over graph-structured data. To support efficient evaluation of path expressions structured indexes have been proposed. However, most variants of structures indexes ignore inter- or intra-document references. They assume a tree-like structure of XML-documents. Extending these indexes to work with large XML graphs and to support intra-or inter-document links requires a lot of computing power for the creation process and a lot of space to store the indexes. Moreover, the efficient evaluation of ancestors-descendants queries over arbitrary graphs with long paths is a severe problem. In this paper, we propose a scalable path index that is based on the concept of 2-hop covers as introduced by Cohen el al. The proposed algo-rithm for index creation scales down the original graph size substantially. As a result a directed acyclic graph with a smaller number of nodes and edges will emerge. This reduces the n...