Constraints: Restricting the Allowed Values 
Constraints: Restricting the Allowed Values
You can use the INFERENCES section of a constraint to restrict the allowed values of a restrictable characteristic, as well as to infer values, if:
Restricting the allowed values puts a heavy load on system performance.
If you use tables to restrict allowed values, the system load depends on the size of the table and the number of columns in the table for which values are inferred.
You have various options for restricting the allowed values.
Restricting Allowed Values with Tables
You can refer to tables in a constraint to restrict the allowed values of a characteristic dynamically.
You can define allowed combinations of values by maintaining the table. You can refer to the table in a constraint. The allowed values for characteristics can then be restricted according to the combinations of values maintained in the table.For more information on working with tables, see
Tables in Constraints.Restricting Allowed Values with IN
You can also specify allowed values by using the expression IN:
OBJECTS:
PC IS_A (300) PC
WHERE C = CASING;HD = HARD_DISK.
RESTRICTIONS:
HD IN (1275, 1620, 2000) IF C = Tower.
INFERENCES:
HD.
Restricting Allowed Values with a Linear Function
This type of restriction is only possible for numeric characteristics.
In the RESTRICTIONS part of a constraint, you can enter a restriction for restrictable numeric characteristics in the form f(x) < 0 (right-hand side constant value) such that f(x) is a linear expression in variable X. Any other comparison operator can be used in the place of '<'. 
RESTRICTIONS:
5L - 20 > 0
Restricting Allowed Values with Comparisons
You can restrict the allowed values of alphanumeric characteristics by comparing two alphanumeric characteristics.
OBJECTS:
PC is_a (300)PC
RESTRICTIONS:
PC.COLOR_1 = PC.COLOR_2
INFERENCES:
PC.COLOR_1
COLOR_1 and COLOR_2 are restrictable characteristics.
The constraint assigns the values of characteristic COLOR_2 to characteristic COLOR_1.
