Editing Document retrieval (section)

===Content based===
The content based approach exploits semantic connections between documents and parts thereof, and semantic connections between queries and documents. Most content based document retrieval systems use an [[inverted index]] algorithm.

A ''signature file'' is a technique that creates a ''quick and dirty'' filter, for example a [[Bloom filter]], that will keep all the documents that match to the query and ''hopefully'' a few ones that do not. The way this is done is by creating for each file a signature, typically a hash coded version. One method is superimposed coding. A post-processing step is done to discard the false alarms. Since in most cases this structure is inferior to [[inverted file]]s in terms of speed, size and functionality, it is not used widely. However, with proper parameters it can beat the inverted files in certain environments.