BizTalk Server includes a
workflow platform, which allows us to graphically create executable,
long-running, stateful processes. These workflows, called orchestrations,
are designed in Visual Studio.NET and executed on the BizTalk Server.
The Orchestration Designer in Visual Studio.NET includes a rich palette
of shapes we can use to build robust workflows consisting of control
flow, message manipulation, service consumption, and much more. The
Orchestration Runtime is responsible for executing the orchestrations
and managing their state data.
Orchestration is a
purely optional part of a BizTalk solution. You can design a complete
application that consists solely of message routing ports. In fact, many
of the service-oriented patterns that we visit throughout this book
will not require an orchestration. That said, there are a number of
scenarios where injecting orchestrations into the solution makes sense.
For instance, instead of subscribing directly to the "new employee"
message, perhaps a payroll system will need additional data (such as
bank information for a direct deposit) not currently available in the
original employee message. We could decide to create a workflow, which
first inserts the available information into the payroll system, and
then sends a message to the new employee asking for additional data
points. The workflow would then wait for and process the employee's
response and conclude by updating the record in the payroll system with
the new information. BizTalk orchestrations are a good fit for
automating manual processes, or choreographing a series of disconnected
services or processes to form a single workflow.
Orchestration "shapes" such as Decide,
Transform, Send, Receive, and Loop are used to build our orchestration
diagrams like the one below. This particular diagram below shows a
message leaving the orchestration, and then another message returning
later on in the flow. How does that message know which running
orchestration instance to come back to? What if we have a thousand of
these individual processes in flight at a single point in time? BizTalk
Server has the concept of correlation which means that you can identify a unique set
of attributes for a given message which will help it find its way to
the appropriate running orchestration instance. A correlation attribute
might be as simple as a unique invoice identifier, or a composite key
made up of a person's name, order date, and zip code.
