As seen from the examples in the previous section, a PROC OPTMODEL model consists of one or more declarations of variables, objectives, constraints, and parameters, in addition to possibly intermixed programming statements, which use the components that are created by the declarations. The declarations define the mathematical form of the problem to solve. The programming statements define data values, invoke the solver, or print the results. This section describes some basic concepts, such as variables, indices, and so on, which are used in the section Syntax: OPTMODEL Procedure.