UNKNOWN


Use the '?' (question mark), representing UNKNOWN, to check if an expression or an attribute has a value.

Example

Suppose a model with an entity Person and attributes Person.name and Person.age. In runtime, a user fills out a form and enters his name, but forgets to fill out his age.

As a result:

ExpressionResultTypeReason
Person.name = ?FALSEbooleanThis attribute is filled out
Person.age = ?TRUEbooleanThis attribute is not filled out, and therefore UNKNOWN

TRUE


This is the boolean value TRUE.

FALSE


This is the boolean value FALSE.