11. A method according to claim 1 wherein said second set of nodes comprises one or more child nodes of at least one parent node in said first view of the hierarchical data source not lying along said directed path from said ancestor node to said compulsory entity.
13. A method according to claim 11 wherein, step (iv) comprises selecting said child nodes as a set of context entities from all child nodes of said parent node, said selecting comprising the steps of (iv-a) computing a first occurrence probability of said parent node appearing without any of its child nodes given the occurrence probability of said parent node, the ancestor node and said compulsory entity; and if said first occurrence probability is less than or equal to 0.5: (iv-b) computing a second occurrence probability of each of the child nodes of said parent node given the occurrence probability of said parent node the ancestor node and said compulsory entity; (iv-c) computing a total sum of said second occurrence probabilities of all child nodes of said parent node, and (iv-d) selecting the set of context entities from the set of all child nodes of said parent node in order of descending values of said second occurrence probability until the sum of said second occurrence probability of selected nodes equals or exceeds half of said total sum, wherein said first occurrence probability and said second occurrence probability are approximated using an occurrence probability of a node in said hierarchical data source, a co-occurrence probability between a pair of nodes in said hierarchical data source, and a joint-occurrence probability between an n-tuple of nodes in said hierarchical data source observed in at least one said previous view.