11. A method as claimed in claim 10 , wherein matching of an input stimulus to an associated output instruction is initially limited to looking within one level of the data structure and will only search outside the level if a match is not found.
11. A method as claimed in claim 10 , wherein matching of an input stimulus to an associated output instruction is initially limited to looking within one level of the data structure and will only search outside the level if a match is not found. 12. A method as claimed in claim 11 , wherein a previous level within which a match was found is recorded which initiates the next search for a match within the same level.