Defining Constraints

The OBJECTS part is optional. It can be omitted if only the three instances $self, $parent, and $root are to be addressed and no variables are required.

Watch the following video, which explains the declaration of objects.

In the step, Maintain object keys, you define which fields are used to specify an object. You also enter the field name of the key field. The material number key field is referred to by formal parameter NR. An object key can consist of several partial keys, as is the case for documents:

(Document)(017)(TYPE = 'DRW', VERSION = '00', PART = '000', NR = 'D4545')

For the class type, enter the class type of the class to which the object is assigned. If the object is not assigned to a class, do not enter a class type. However, you must enter empty parentheses as a place holder.

(Material)()(NR = 'MAT-A')

The following figure shows you the variable definition in the object part.

If you use a class to refer to an object, you use the expression IS_A to define a variable: X IS_A (300) T_FC00.

If you refer to an object using the object key, and do not enter a class, you use the expression IS_OBJECT to define a variable: Y IS_OBJECT (Material)(300)(NR=T-FC00).

Variables for the $self, $part, and $root instances are defined using the keyword AS: Z AS $SELF

If you use the object key to refer to an object, you must define a variable. If you use a class or an instance to refer to an object, defining a variable is optional.

You can enter a ? to make your variables easier to identify: ?X IS_A (300) T_FC00.

The variables referred to in a constraint must already be known when you create a constraint.

Constraint – Example without variables:

1234
OBJECTS:     (300)T_FC498  , 
             (300)T_FC598  . 
CONDITION: (300)T_FC598.T_FC004 specified .
RESTRICTION:  (300)T_FC598.t_FC003 = (300)T_FC498.t_FC022 .

Constraint – Example with variables:

1234
OOBJECTS:     ?carr is_a (300)T_FC498  ,
              ?cab  is_a (300)T_FC598  .
CONDITION:    ?cab.T_FC004 specified .
RESTRICTION:  ?cab.t_FC003 = ?carr.t_FC022.

Constraint – Example with characteristic variables:

123456
OBJECTS:     (300)T_FC498  where  wheels = T_FC022  ,
             (300)T_FC598  where  seat = T_FC003    ;
                                  back = T_FC004    .
CONDITION:  specified back .
RESTRICTION:  seat = wheels.

The following figure shows you variable examples in the object part.

Advantages of variables:

• Self-explanatory names

• Easier to maintain subsequent sections of constraint

• Less code

It's entirely up to you whether you use variables or not. Variables are an option for supporting modeling. Characteristic variables can be used in conjunction with object variables and class variables.

The inferences section can only contain characteristic variables.

If you use a table call or a function call, the relevant access keys must be defined there (value assignment alternative of a table or function).

If you use arithmetical expressions, it must be possible to interpret a variable.

Watch the following video, and understand the definition of Constraints with formulas and inferences.