What is the main concern of the open source workflow engine core?

JBPM is the most prominent of the open source workflow engine, which is now used in a wide range of areas. At present, the open source workflow engine has many, different open source workflow engine, whether design or implementation is different, its selection, algorithm, mechanism and so on. Speaking of the open source workflow engine core, I believe that the most concern of the people is the engine core problem. What is the most interesting thing about the engine core of an open source workflow? Let's take a look at:
In fact, the engine kernel is focused on an abstract level of the problem, its responsibilities are very streamlined, mainly to ensure that the process from one node to another node, to ensure that the current node can be executed. In summary, the open source workflow engine core concerns four aspects, the following points:

1. The definition of a process: the so-called process definition does not mean a graphical definition, but rather the flexibility to use the definition object to interpret the process to be defined. The definition of a process is very important, and it is the beginning of an open source workflow that will have a big impact on future workflows. During the process of process definition, we should make the specific optimization method of business process, and know that the future business process work smoothly.
2. Process scheduling problem: In the process of scheduling, the use of relevant mechanisms to ensure that a simple process to solve some complex problems, such as in the process encountered in the serial, branch, parallel, aggregation, and so on, to ensure that the complex process can be run from one node smoothly to another node.
3. Process Execution issues: When an open source workflow is run to a node, a set of mechanisms is needed to resolve it. Whether you want to execute this node or not, how to execute it is also done by mechanism, which ensures that the nodes of open source work remain in the normal life cycle.
4. Process instance objects: In an open source workflow process, a complete set of process instance objects is required to describe the strength process, which describes the process state and its results.

What is the main concern of the open source workflow engine core?