1. A method for applying stream processing to a hierarchical self describing data stream, comprising: associating selected elements in a data stream with a set of path expressions and a function; ordering the set of selected path expressions; creating a tree structure corresponding to a hierarchical nature of the path expressions ordering, the tree structure having a root node and at least one child node; creating a filter for each interior node of the tree structure, wherein an interior node is a node with both a parent and at least one child, said filter associated with a node to pass data elements corresponding to a path expression assigned to said node; passing data chunks supplied from the data stream through filters to extract selected elements, wherein the filters are organized into the tree structure and applied to the data stream according to the tree structure; and associating with each path expression an aggregation object to provide support for manipulation of each extracted data element satisfying the path expression according to an aggregation function applied to data elements extracted by said filters.