Actors have one or more value interfaces. A value interface groups precisely one in-going and one out-going value offering.
It shows the mechanism of economic reciprocity. Economic reciprocity refers to rational acting actors. We suppose that actors
are only willing to offer objects to someone else, if they receive adequate compensation (i.e. other value object(s) in an in-going
offering) in return. So, with the value interface, we can model that an actor is willing to o????er something of value to its environment
but requests something in return, whereas a value offering models that objects can only requested or delivered in combination.
The transfer of value objects is atomic at the level of the value interface. Either all ports in a value interface (via value offerings) each precisely transfer one value object instance (or more, depending on the stated port cardinality) or none at all. This ensures that if an actor offers something of value to someone else, it always gets in return what it wants. How this is ensured is a matter of a robust business process design, trust and associated control mechanisms legal agreements, or sometimes use of technology, but this is not expressed by the value model. Also, note that a value interface and value offering do not model in which order value objects are transferred; it is only modeled that value objects are transferred.
|name||A value interface may have a name to refer to it.|
A ‘traveler’ has a value interface with two offerings (each containing two ports), representing that ‘fees’ have to paid in return for a ‘train trip’ and ‘food’.
A value interface is assigned to zero or one actor and consists of two value offerings, namely an out-going offering and an in-going offering. Each actor has its own value interface. Multiple value interfaces can be assigned to an actor and a value offering belongs to exactly one value interface.