Suppose we want to encode the Webster's English dictionary which contains about 159,000 entries. Find a way to build the dictionary adaptively. Original methods due to Ziv and Lempel in 1977 and 1978. It is used in UNIX compress . Monitor compression performance and flush dictionary when performance is poor.
Table lookup is automatic.
Summary Huffman maps fixed length symbols to variable length codes. Optimal only when symbol probabilities are powers of 2. Arithmetic maps entire message to real number range based on statistics. Theoretically optimal for long messages, but optimality depends on data model. It maps a variable number of symbols to a fixed length code.