6. The method of claim 2 , further comprising automatically determining the threshold value based on evaluating historical query access patterns and characteristics of nodes of a collection of documents that were accessed in the historical query access patterns.
2. The method of claim 1 , wherein determining whether the characteristics of the sub-tree rooted at said each node meet the first criterion includes: determining whether a suitability metric evaluated over the sub-tree rooted at said each node exceeds a threshold value.