e3value user manual, first release

3.4 Value interfaces and value transactions

A value interface groups incoming and outgoing value ports into an atomic value exchange. A value interface must contain ports of opposite roles, i.e. at least one in-port and one out-port. An interface containing only outgoing or only ingoing ports is impossible. Actors, market segments and value activities may all have value interfaces. We discuss actor value interfaces in this section and interfaces of market segments and activities in later sections.

A value interface is visualized by a rounded box around its ports. Figure 3.1 shows two value interfaces.

Reciprocity. Value interfaces express economic reciprocity, which is the property that a rational actor is only willing to offer objects to another actor if it receives adequate compensation. Usually the compensation for a non-money value object is a reciprocal money object, but this is not a requirement. The reciprocal object may be any value object that the requestor perceives to increase its economic utility.

Atomicity. Transfer of value objects across a value interface is atomic. In an occurrence of a value transfer of a value interface, either all transfers of the value interface occur in the contract period, or none of them is. This ensures that if an actor offers something of value to someone else, it always gets in return what it wants in the same contract period. How this is ensured is a matter of a robust business process design, trust and associated control mechanisms, legal agreements, or technology. This is not expressed in the value model.

Also, value models do not express an ordering of value transfer occurrences. For example, in figure 3.1, the traveller may first pay and make the trip a month later. Or the traveler may pay when entering the railway station, or when entering the train, or pay at the end of the month in which the trip was made. Timing and ordering of actions is not modelled by an e3value model.

What is modeled is that if a value transfer of an interface occurs in the contract period of the model, then all other transfers of the interface also occur in the contract period. This is precisely enough to count the number of occurrences of value transfers, e.g. of payments, and do net value flow computations for a contract period.

Value transaction. A value transaction is the set of value transfers triggered when a value interface is triggered. We will see that value transactions can involve more than two actors and more than two interfaces.