You use Boolean operators in OCL expressions to combine conditions into a result that is either true or false; this page is for modelers writing constraints, selection criteria, and other conditional rules in MDriven.

A Boolean expression answers a yes-or-no question. For example, self.age >= 18 is Boolean because it evaluates whether a person's age meets the condition. You can combine that result with other Boolean expressions by using logical operators.

Use Boolean operators

Operator	Result	Example
and	true only when both conditions are true.	self.age >= 18 and self.hasDriverLicense
or	true when at least one condition is true.	self.category = 'Electronics' or self.category = 'Books'
not	Reverses a Boolean result.	not self.hasDriverLicense

Combine required conditions with and

Use and when every requirement must be met. For example, this condition is true only for a person who is at least 18 and has a driver's license:

self.age >= 18 and self.hasDriverLicense

If either the age condition or the license condition is false, the complete expression is false.

Allow alternatives with or

Use or when either condition is sufficient. For example, this expression identifies a product in either of two categories:

self.category = 'Electronics' or self.category = 'Books'

Both conditions may also be true; the result remains true. For a fuller explanation and additional examples, see Documentation:OCLOperators Or.

Exclude a condition with not

Use not when the rule requires a condition to be false. For example, this expression is true when a person does not have a driver's license:

not self.hasDriverLicense

Group complex conditions

Use parentheses to make the intended grouping clear when you combine and and or. For example, the following rule requires a driver's license and allows either an adult or a person in the Books category:

(self.age >= 18 or self.category = 'Books') and self.hasDriverLicense

Parentheses make the alternatives explicit before the final license requirement is evaluated. Review OCL precedence rules when an expression depends on operator evaluation order.

Use Boolean expressions in a collection selection

The select collection operation evaluates a Boolean condition for each object and retains the objects for which the condition is true. Name the iterated object before the pipe character (|) and use that name in the condition.

For example, to select cars that are registered and have a positive registration number:

self.cars->select(oneCar | oneCar.isRegistered and oneCar.registrationNumber > 0)

Here, oneCar is the loop variable. The expression after | must produce a Boolean result for each car. Learn more about collection-specific operations in Documentation:OCL Collection Operators and see the expression walkthrough in Documentation:Turnkey session 7: Expressions.

Use Boolean expressions in MDriven

MDriven uses OCL as a query language. An OCL expression must not have side effects: evaluating it is not expected to change data. Boolean expressions can be used in several places, including:

• Constraints on a class.
• Derivation rules for derived attributes and associations.
• ViewModel column visibility and enable-state expressions.
• ViewModel column style expressions.
• Action enable expressions.
• State-machine guards.

For example, an action enable expression can use self.age >= 18 and self.hasDriverLicense so that the action is enabled only when both requirements hold.

Find operators in the OCL Editor

To explore operators available for a model type, open the OCL Editor and type a class. The editor shows the available operators for that context. See Documentation:OCL General Operators for this approach and Documentation:OCLOperators for the general operator overview.

See also

• Documentation:OCL Expressions
• Documentation:OCLOperators
• Documentation:OCLOperators Or
• Documentation:OCL Collection Operators
• Documentation:Part 2 OCL: Operators