In order to perform any task with MOSES, one must be able to communicate with the program in a language understandable by both the user and the program. In this section, the rules of grammar and syntax of the language employed and the general operation of MOSES will be discussed.

In discussing the various types of commands, some of the words are "set off". By "set off", we mean the words are either underlined or printed in bold type, depending on the method used to print this manual. These words are keywords, either commands or options, and must be input exactly as written. The characters not "set off" represent the data which takes on the appropriate numeric or alphanumeric value. In some cases, an underline is part of an option or command. For example, END_DISPOSE is a command. In keeping with the format of this manual, these commands are "set off" (and possibly underlined), and the user needs to remember that the underline exists as part of the command.

MOSES provides many features of a programming language. In MOSES, one can alter the flow of either command or description input, make logical checks, define variables, create macros, etc. All of these features operate on both commands and descriptions, so that with this language one can automate the definition of a model as well as build a set of specific commands he needs to perform repetitive tasks.