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; and associating with each path expression an aggregation object to provide support for manipulation of each data element satisfying the path expression according to an aggregation function.