e3value user manual, first release
An or-dependency is logical disjunction of dependencies. It is a represented by a small tree with a connection point at its root that represents the disjunction and connection points at its leaves that represent the parts of the disjunction, called the disjuncts. For example, in figure 4.7, a = (b or c or d). By this we mean that
a occurs in the contract period of the model if and only if exactly one of b, c or d occurs in the contract period of the model.
A dependency path may pas through an or-dependency.
For example, in figure 4.8, the Luxury transporting value activity chooses between two suppliers of food. For each occurence of the customer need, one of the two suppliers supplies the food. How and when these choices are made is not represented. The choice may be made once per year, once per month, based on external conditions, per group of travelers, or in other ways. A value model does not provide process information.
We can construct complex and-or logic by combining and- and or-dependencies. In figure 4.9, each time the traveler need occurs, the traveler makes the choice whether or not to combine the purchase of a train trip with the purchase of food. The upper choice in the diagram leads to a purchase of a train trip only. The lower choice leads to a purchase of a train trip and of food.