9. The system as recited in claim 8 further comprising: means for summing the signatures of the first and associated documents to create an aggregate signature; means for selecting a set of words from the aggregate signature based on their aggregate number of occurrences in the first and associated documents; and means for constructing a search statement from the selected set of words.
8. A system including processor, memory and display for retrieving computerized documents from a document database comprising: means for retrieving documents according to a first search statement; means for developing signatures for a plurality of documents by searching for words in the documents and removing common words which occur in a relatively high frequency in a natural language in which the documents are written; means for automatically associating selected ones of the documents with a first document according to a degree of match of the signatures of the selected documents with the signature of the first document; means for displaying the first document; means responsive to a user indication that a second search is to be made for automatically selecting a set of words from an aggregate signature based on the signatures of the first and associated documents and the aggregate number of occurrences of the set of words in the first and associated documents; and means for constructing a second search statement from the selected set of words.