This manual describes information processing procedures for Museum Computer Network (MCN) systems. The first section contains general rules for preparation of input: conventions for all data; conventions for controlling the appearance of output; conventions for automatic sorting of data; conventions for user specified sorting of data; and conventions for self-defining structures. The second section consists of a list of tags recognized by the MCN. The definition and syntax rules for each tag are given along with an illustration of its use. Five pages appended at the end provide information on new data classes created since the printing of the manual. (CH)