Expression specification (UML)
An expression specification (Engl. InstanceSpecification ) is a model element in the Unified Modeling Language (UML), a modeling language for software and other systems.
description
An occurrence specification specifies a concrete entity in a modeled system. It specifies selected aspects of this entity, in particular what name it has and which classifier it is an instance or instance. It can also declare a specific value for each structural feature of the classifier. The UML2 designates the name of a structural feature combined with a specific value as a slot .
Expression specifications can be used very flexibly. For example, a modeler does not have to specify a name. Furthermore, no or more classifiers can be assigned to the expression specification.
The graphic representation of an occurrence specification only differs in details from that of a class . First, the name of the expression is followed by a colon and the name of the classifier of which the expression is an instance. This text is always underlined. Second, the slots areName = Wert specified in the form in an area of the enclosing rectangle .
The second figure shows an occurrence specification for an anonymous occurrence . This example also shows that in addition to the name and value of a slot, its type can also be listed in the graphic notation.
Expression specification and associations
An association can also have characteristics as there can be a class, because both are specializations of classifiers. The expression of an association is called an object relationship or link . The graphic notation for a link largely corresponds to the graphic notation for an association. The figure on the right shows an occurrence specification for an object relationship between two occurrences of the classifier Person.
Differences to UML 1.4
Neither the Object model element nor the Link model element from UML 1.4 was adopted in UML2. Both have been replaced by expression specification .