Sommerville-Software-Engineering-10ed

546 Chapter 18 ■ Service-oriented software engineering
SetupComputation
Request
processor
Store
results
OK
No processor
Set up job
parameters
Report
completion
Download
data
Restart
Fail
OK
Start
computation
VectorProcService
Check
Availability
Return
results
Allocate
resources
Initialize
Compute
Figure 18.16 Interacting
workflows
Carry out the computation
Return the results to the client service
In BPMN terms, the workflow for each organization is represented in a separate
pool. It is shown graphically by enclosing the workflow for each participant in the
process in a rectangle, with the name written vertically on the left edge. The workflows
in each pool are coordinated by exchanging messages. In situations where
different parts of an organization are involved in a workflow, pools are divided into
named “lanes.” Each lane shows the activities in that part of the organization.
Once a business process model has been designed, it has to be refined depending
on the services that have been discovered. As I suggested in the discussion of Figure
18.14, the model may go through a number of iterations until a design that allows the
maximum possible reuse of available services has been created.
Once the final design is available, you can then develop the final service-oriented
system. This involves implementing services that are not available for reuse and converting
the workflow model into an executable program. As services are implementation-language
independent, new services can be written in any language. The workflow
model may be automatically processed to create an executable WS-BPEL model if
SOAP-based services are used. Alternatively, if RESTful services are used, the workflow
may be manually programmed, with the model acting as a program specification.
18.4.2 Testing service compositions
Testing is important in all system development processes as it demonstrates that a
system meets its functional and non-functional requirements and detects defects that