Abstract: Effectively storing and querying XMI. documents becomes a hot research topic on current database domain. In the light of path summary, path-partitioned encoding scheme was proposed to store an XMI_ document, and useful for eliminating descendant axes and wildcards in twig queries. For twig queries without“//，，or“、”，a new query algorithm　was developed based on structurcconstraincd nodes, so structural joins extremely decreases. The results of experimenu indicate the algorithm can significantly filter useless elements and improve the performance for twig queries.

Key words: XML, Twig query, Structural j oin, Path summary