1. A method comprising steps of: receiving one or more criteria that identifies particular nodes within one or more XML documents to exclude from query evaluation; based on the one or more criteria, generating a representation of the one or more XML documents that excludes the particular nodes; receiving a query that specifies a path operation based on a path, wherein one or more of said particular nodes is under said path in the one or more XML documents; and using the representation to compute the path operation as if the one or more of said particular nodes are not in the one or more XML documents; wherein the steps are performed by one or more computing devices.