  As the number of services and the size of data involved in workflows
increases, centralised orchestration techniques are reaching the limits of
scalability. In the classic orchestration model, all data passes through a
centralised engine, which results in unnecessary data transfer, wasted
bandwidth and the engine to become a bottleneck to the execution of a workflow.
  This paper presents and evaluates the Circulate architecture which maintains
the robustness and simplicity of centralised orchestration, but facilitates
choreography by allowing services to exchange data directly with one another.
Circulate could be realised within any existing workflow framework, in this
paper, we focus on WS-Circulate, a Web services based implementation.
  Taking inspiration from the Montage workflow, a number of common workflow
patterns (sequence, fan-in and fan-out), input to output data size
relationships and network configurations are identified and evaluated. The
performance analysis concludes that a substantial reduction in communication
overhead results in a 2-4 fold performance benefit across all patterns. An
end-to-end pattern through the Montage workflow results in an 8 fold
performance benefit and demonstrates how the advantage of using the Circulate
architecture increases as the complexity of a workflow grows.
