UNKNOWNYou can 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: Expression | Result | Type | Reason |
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Person.name = ? |
returns FALSE since this | FALSE | Boolean | This attribute is filled out | Person.age = ? |
returns TRUE since this | TRUE | Boolean | This attribute is not filled out, and therefore |
is
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