In the flow activity, the BPEL code determines the number of parallel branches. However, often the number of branches required is different depending on the available information. The flowN activity creates multiple flows equal to the value of N, which is defined at runtime based on the data available and logic within the process. An index variable increments each time a new branch is created, until the index variable reaches the value of N.

The flowN activity performs activities on an arbitrary number of data elements. As the number of elements changes, the BPEL process service component adjusts accordingly.

The branches created by flowN perform the same activities, but use different data. Each branch uses the index variable to look up input variables. The index variable can be used in the XPath expression to acquire the data specific for that branch.

For example, suppose there is an array of data. The BPEL process service component uses a count function to determine the number of elements in the array. The process then sets N to be the number of elements. The index variable starts at a preset value (zero is the default), and flowN creates branches to retrieve each element of the array and perform activities using data contained in that element. These branches are generated and performed in parallel, using all the values between the initial index value and N. The flowN activity terminates when the index variable reaches the value of N. For example, if the array contains 3 elements, N is set to 3. Assuming the index variable begins at 1, the flowN activity creates three parallel branches with indexes 1, 2, and 3.

The flowN activity can use data from other sources as well, including data obtained from web services.

Figure 10-15 shows the runtime flow of a flowN activity in Oracle Enterprise Manager Fusion Middleware Control that looks up three hotels. This is different from the view, because instead of showing the BPEL process service component, it shows how the process has actually executed. In this case, there are three hotels, but the number of branches changes to match the number of hotels available.