Objects and Classes - Assigning Value - Expressions

3 important questions on Objects and Classes - Assigning Value - Expressions

You can use a literal or an indirect literal via an instance specification to assign a value to a property or slot as we have seen, but you can also use an OPAQUE EXPRESSION.

Wht is an Opaque Expression?

An opaque expression is an expression in a language that is opaque to UML. In this usage, “opaque” means “hidden” and that it is unparsable directly in UML.

If necessary, you can specify the target language by preceding the opaque expression string with the language name displayed in.....?

braces ({}).

In UML, most : ................. Are written as opaque expressions

In UML, most :
  • expressions
  • constraints
  • guard conditions
  • descriptions of behavior
  • and pseudocode


are written as opaque expressions.


As opaque expressions are not automatically parsed, constraints in UML are not always strictly in Boolean form as shown in Fig. 6.7

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