A Constraint is a condition that limits the values of one or more columns in a table. A Constraint is defined either on the Constraints card within the table design or within a Domain.
Relationship between a constraint and other objects:
1. Table Uses Constraint
1. A table can have constraint definitions; a constraint is uniquely assigned to a table (1-N[0]). A domain constraint can be used in a number of tables (N[0]-M[0]).
It is possible to display a list of Constraints from the main menu. This can be helpful if you wish to have an overview of existing Constraints along with their names.
Select the Object / Design function from the constraint list or click on the 
toolbar button to activate design mode for the associated table. This opens the
Constraint card, where you can define additional Constraints for the table as described in Section Defining Constraints.