FAST is an acronym for FIX Adapted for Streaming.
Although the original purpose of FAST was optimization of FIX messages, the encoding method defined in this document has been generalized to apply to a wider set of protocols.
The encoding method reduces the size of a data stream on two levels. First, a concept referred to as Field Operators allows data affinities of a stream to be leveraged and redundant data to be removed. Second, serialization of the remaining data is accomplished through binary encoding which draws on self-describing field lengths and bit maps indicating the presence or absence of fields.
The encoding is performed with respect to a control structure called a template. A template controls the encoding of a portion of the stream by specifying the order and structure of fields, their field operators and the binary encoding representations to use
The term encode refers to the process of serializing an instance of an application type to a FAST stream.
The term decode refers to the process of deserializing a part of a FAST stream into an instance of an application type.