Extraction, Transformation, and Loading - Data Warehouse Systems: Design and Implementation - page 282

a b

Fig. 8.1 Activities. ( a ) Single task. ( b ) Collapsed and expanded subprocess

or subprocesses, and thus they can be atomic or nonatomic. Figure 8.1 a
shows how a task is represented. A subprocess is an encapsulated process
whose details we want to hide. Figure 8.1 b shows that there are two ways of
representing a subprocess: collapsed and expanded.

a

Exclusive Inclusive Parallel Complex

b

Splitting Merging

Fig. 8.2 ( a ) Different types of gateways. ( b ) Splitting and merging gateways

Gateways are used to control the sequence of activities in a process
depending on conditions . It is worth noting that BPMN does not state how
these conditions must be written; this is left to the modeler. Gateways are
represented by diamond shapes. BPMN defines several types of gateways,
showninFig. 8.2 a, which are distinguished by the symbol used inside the
diamond shape. All these types can be splitting or merging gateways,
as shown in Fig. 8.2 b, depending on the number of ingoing and outgoing
branches. An exclusive gateway models an exclusive OR decision, that is,
depending on a condition, the gateway activates exactly one of its outgoing
branches. It can be represented as an empty diamond shape or a diamond
shapewithan' X ' inside. A default flow (see below) can be defined as one
of the outgoing flows, if no other condition is true. An inclusive gateway
triggers or merges one or more flows. In a splitting inclusive gateway, any
combination of outgoing flows can be triggered. However, a default flow
cannot be included in such a combination. In a merging inclusive gateway,