If a constraint is a logical AND, the precedence constraint line is solid. If it is set to OR, the line is
dotted. This is useful if you want to be notified when any one of the tasks fails by using the logical
OR constraint.
In the Evaluation Operation dropdown, you can edit how the task will be evaluated:
➤➤ Constraint: Evaluates the success, failure, or completion of the predecessor task or tasks
➤➤ Expression: Evaluates the success of a customized condition that is programmed using an
expression
➤➤ Expression and Constraint: Evaluates both the expression and the constraint before moving
to the next task
➤➤ Expression or Constraint: Determines whether either the expression or the constraint has
been successfully met before moving to the next task
If you select Expression or one of its variants as your option, you’ll be able to type an expression
in the Expression box. An expression is usually used to evaluate a variable before proceeding to
the next task. For example, if you want to ensure that InputFileVariable variable is equal to the
Variable2 variable, you would use the following syntax in the Expression box:
@InputFileVariable == @Variable2
You can also single-click the constraint and use the Properties window on the right to set these
properties, if you prefer not to use the editor.
Now that you know more about constraints, it’s a good time to look at a scenario and how the
constraints apply to your environment. The example shown in Figure 2-17 demonstrates how
flexible precedence constraints can be. The first Script Task runs a script to determine whether the