Incremental Encoders

Incremental encoding, also known as front compression, back compression or front coding, is a type of delta encoding compression algorithm whereby common prefixes or suffixes and their lengths are recorded so that they need not be duplicated. This algorithm is particularly well suited for compressing sorted data, e.g. a list of words from a dictionary. The encoding used to store the common prefix length itself varies from application to application. Typical techniques are storing the value as a single byte; delta encoding, which store only the change in the common prefix length; and various universal codes. It may be combined with other general lossless data compression techniques such as entropy encoding and dictionary coders to compress the remaining suffixes. Incremental encoding is widely used in information retrieval to compress the lexicons used in search indexes; these list all the words found in all the documents and a pointer for each one to a list of locations. Typically, it compresses these indexes by about 40%.