Information Technology Reference
In-Depth Information
The process engine
The process engine is the module that is in charge of the actual execution of our business
processes. It creates new process instances and keeps track of their state and their internal
steps. Its job is to expose methods to inject process definitions and to create, start, and
continue our process instances.
Understanding how the process engine works internally is a very important task for the
people involved in BPM's stage 4, that is, runtime. This is where different configurations
can be used to improve performance, integrate with other systems, provide fault tolerance,
clustering, and many other functionalities.
Process Engine structure
In the case of jBPM6, process definitions and process instances have similar structures but
completely different objectives. Process definitions only show the steps it should follow
and the internal structures of the process, keeping track of all the parameters it should
have. Process instances, on the other hand, should carry all of the information of each pro-
cess's execution, and have a strategy for handling each step of the process and keep track
of all its actual internal values.
Process definition structures
These structures are static representations of our business processes. In
Chapter 3
,
Using
BPMN 2.0 to Model Business Scenarios
, we will see how these representations can be
written by technical people and different domain experts in detail; we do this using an
XML standard called BPMN 2.0 for process definition and graphical representation.
However, from the process engine's internal perspective, these representations are far
from the actual process structure that the engine is prepared to handle. In order for the en-
gine to get those structures generated, it requires the previously described semantic mod-
ule to transform those representations into the required object structure.
