Alternatively, the joinSpec may consist of an Expression with the name of a single Boolean operator and no operands specified. In this case, the value of the joinSpec shall be given by applying the given operator to Boolean values indicating ... Source Unified Modeling Language 2.5.1
UML2 ValueSpecification - metaclasses - ADVANCED REFERENCE ONLY This content has been marked as discussing an ADVANCED topic! Gallery Tutorial TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo Section 01:02: UML 101 for model-based systems engineering with SysML Slide kind UML Profile Diagram
The String value of a StringExpression is obtained by concatenating, in order, the String values of either the operands or the subExpressions, depending on which is given. Source Unified Modeling Language 2.5.1
The substrings are given as either a list of LiteralString operands or as a list of StringExpression subExpressions (but it is not allowed to mix the two). Source Unified Modeling Language 2.5.1
A StringExpression is an Expression that specifies a String value that is derived by concatenating a list of substrings. Source Unified Modeling Language 2.5.1
Expressions are ValueSpecifications that specify values resulting from a computation. Source Unified Modeling Language 2.5.1