111 defined-word schemes the set of source messages is defined before invocation of the coding scheme. Both of the above example codes are distinct uniquely decodable - A distinct code in which each codeword is identifiable when immersed in a sequence of codewords. Only the block-block example code above is uniquely decodable. The above block-block code is a prefix code. The other is not.
Prefix codes are instantaneously decodable.
This minimality constraint prevents codewords from being longer than they need to be. The mapping from messages to codewords is static. The above two examples are static. The mapping of messages to codewords changes as the encoding process proceeds. Some static codes require two passes.