1. A system for providing a search result for a query, the search result being derived from hierarchically organized documents, comprising: a search component that identifies documents that are relevant to a query based on a feature of the documents; a subtree feature calculation component that calculates a subtree feature for an identified document based on a contribution of the feature of the identified document and a contribution of the feature from its descendant documents; and a relevance component that determines the relevance of the identified documents to the query based on the calculated subtree feature of the identified documents.