3. The method of claim 1 , wherein said constructing said inverted index comprises: generating a full path token and a full path token posting list associated therewith by said inverted index, said full path token posting list including a plurality of identifiers representing said plurality of documents, wherein an identifier of said plurality of identifiers represents said document and includes a payload value, said payload value identifying a full path of said document in said tree structure, and said payload value including a set of full path indicators provided by a scheme that uniquely labels each sibling node of said tree structure.
3. The method of claim 1 , wherein said constructing said inverted index comprises: generating a full path token and a full path token posting list associated therewith by said inverted index, said full path token posting list including a plurality of identifiers representing said plurality of documents, wherein an identifier of said plurality of identifiers represents said document and includes a payload value, said payload value identifying a full path of said document in said tree structure, and said payload value including a set of full path indicators provided by a scheme that uniquely labels each sibling node of said tree structure. 4. The method of claim 3 , further comprising: building a hierarchy of a plurality of counters, each counter being associated with a node of said plurality of nodes of said tree structure, wherein a counter of said plurality of counters is indexed by said set of full path indicators; and updating a value stored in said counter, said value indicating a count of one or more documents of said plurality of documents, said one or more documents categorized by a sub-category of a category or sub-category indicated by a constraint of said plurality of constraints.