19. The computer program product of claim 15 , wherein providing a representation comprises: providing the representation after each document in the plurality of multi-word documents has been associated with to at least one topic cluster corresponding to a sub-node in the hierarchy, wherein any of the plurality of multi-word documents may be associated to more than one topic cluster based on different portions of the respective document.
15. A computer program product, comprising a computer usable medium having a computer readable program code embodied therein, the computer readable program code adapted to be executed by a computer to implement a method for clustering a plurality of multi-word documents, wherein each document includes a plurality of words and is represented as a set of (document,word) pairs, represented as documents and words (i,j) into a hierarchical data structure including a root node successively split to produce a plurality of sub-nodes, wherein each sub-node is associated with a topic cluster based on the plurality of documents, the method comprising: retrieving a first document; associating the first document with a first topic cluster based on a first portion of the first document; associating the first document with a second topic cluster based on a second portion of the document; and providing a representation of topics associated with the plurality of multi-word documents based on the hierarchical data structure including the first and second topic clusters, wherein the first and second topic clusters are associated with a different sub-node, wherein a probability of observing any pair of co-occurring objects represented as the set of (document,word) pairs, the document of the pairs being (i) and the words being (j), is modeled by defining a variable I rα which controls assignment of documents to the hierarchy, such that it is dependent on a particular (document,word) pair (i,j) under consideration during a topical clustering process, and a class α ranges over all nodes in an induced hierarchy in order to assign a document (i object) to any node in the hierarchy, not just leaf nodes, and a class v is defined as an ancestor of α in the hierarchy, the constraint on v ensuring that the nodes are hierarchically organized.