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XML is represented as a tree and the query as a regular path expression. The query is evaluated by traversing each node of the tree. Several indexes are proposed for regular path expressions. In same cases these indexes may not cover all possible paths because of storage requirements. We propose a signature-based query optimization technique to minimize the number of nodes retrieved from the database when the indexes cannot be used. The signature is a hint attached to each node, and is used to prune unnecessary sub-trees as early as possible when traversing nodes. For this goal, we propose a signature-based DOM(s-DOM) as a storage model and a signature-based query executor(s-NFA). Our experimental results show that the signature method outperforms the original.