11.5. Alternate Resource Pools

Certain activities allow alternative resources, when no standard resources are available. For instance, in a pizza service company, when no order taker is available, and a new order call comes in, an available pizza baker can take the order. Or in a hospital, where nurses guide patients to an examination room, when no nurse is available, a receptionist can guide a patient to an examination room.

The general conceptual pattern is that for certain types of activities A (like GuideToRoom), a resource role r (like guide) may be played not only by instances of its direct resource type R (like Guide), but also by instances of an alternative resource type R' (like ExaminationAssistant) or an organizational position P (like Nurse), if they are a subtypes of R (Guide).

When the resource type R is not abstract, then its instances are the preferred resources of activities of type A, and its (possibly preference-rank-annotated) alternate resource subtypes specify types of alternative resources.

By default, for any non-abstract resource type R and for any organizational position P assigned as the range of a resource role r, an OE simulator can create a resource pool with the same (yet pluralized) name, pooling objects instantiating R or P, and assign it to r as the preferred resource pool.

An alternate resource pool can be defined in an OE class model by means of an alternate resource subtyping arrow (a UML generalization arrow designated with «ar») between the alternative resource type and the resource type concerned as shown in the following diagram, where PizzaMaker is modeled as an alternative resource subtype of OrderTaker: