US Patent 7624274 Decreasing the fragility of duplicate document detecting algorithms

In a signature-based duplicate detection system, multiple different lexicons are used to generate a signature for a document that comprises multiple sub-signatures. The signature of an e-mail or other document may be defined as the set of signatures generated based on the multiple different lexicons. When a collection of sub-signatures is used as a document's signature, two documents may be considered as being duplicates when a sub-signature generated based on a particular lexicon in the collection for the first document matches a signature generated based on the same lexicon in the collection for the second document.