The natural visualization of a business process is of boxes and arrows arranged in a tree-like formation. A large process with numerous conditional paths forms a rather expansive tree that can't fir on a computer screen or printed page. If the process has loops, these are often represented as arrows pointing back to earlier boxes, resulting in an untidy graph structure. Although BPEL isn't a visual process language, its XML representation can form code trees that are no less cumbersome. A receive inside a sequence inside a flow inside a switch inside a pick, even if properly indented, can make a coder see double.
This technique article shows how to model BPEL 1.1 processes in a special flat form that represents even the most onerous processes in just a few levels of structure. A process modeled in this form, represented visually, more closely resembles a neat pile of sticks than a tree. Aesthetics aside, the flat approach is fundamentally better suited to SOA orchestration than the tree approach. Flat BPEL is good SOA.
