Introduction

    jPDL是一种直观的流程语言，用以展现商业逻辑的处理过程。jPDL包含的概念涉及任务、异步通讯状态、定时器、自动执行的动作等，为此，为了整合上述行为，jPDL提供了强大、可扩展的控制流机制。

graph based execution languages

implementation technique for graph based execution languages：

    • based on runtime interpretation of a graph. 
    • based on message queues
    • code generation.

The strategy on how graph execution can be implemented on top of an OO programming language. For those who are familiar with design patterns, it's a combination of the command pattern and the chain of responsibility pattern.

1、Transitions  可以理解为进入和离开节点的箭头，应该存在多个Transitions  进入一个节点和一个节点有多个离开的Transitions  的情况

the structure of the graph is represented with the classes Node and Transition，而Transition是具有方向性的

image

 

transitions are able to pass the execution from a source node to a destination node with the method take.

transition.take.method

2、execution ，类似petri中的标记，是变迁就绪的前提

An execution (also known as a token) is represented with a class called Execution. An execution has a reference to the current node.

execution.class

3、Node

A node is a command and has an execute method. Subclasses of Node are supposed to override the execute method to implement some specific behaviour for that node type.

When an execution arrives in a node, that node is executed. The Node's execute method is also responsible for propagating the execution. Propagating the execution means that a node can pass the execution that arrived in the node over one of its leaving transitions to the next node.

When a node's execute method does not propagate the execution, it behaves as a wait state.

Also when a new execution is created, it is initialized in some start node and then waits for an event.

An event is given to an execution and it can trigger the execution to start moving. If the event given to an execution relates to a leaving transition of the current node, the execution takes that transition. The execution then will continue to propagate until it enters another node that behaves as a wait state.

node.execute.method

 

So now we can already see that the two main features are supported : wait states and a graphical representation. During wait states, an Execution just points to a node in the graph

4、Actions

An Action is a command with an execute method. Actions can be associated with events.

Synchronous execution

The default propagation of execution is synchronous.