这一节课的内容是一定会出考题的，因为有许多要设计的地方，BPMN 就是 Business Process Modeling Notation
Business Process Modeling Notation (BPMN)
– Object Management Group (OMG) standard
– Modeling oriented; business oriented
– From version 2.0: formal execution semantics
• Translation to BPEL
具体空洞的理论可以看网页
http://www.bpmn.org/
比较重要的是看这种BPMN图，
一定是有start 和 end event，并且中间不会陷入锁死状态。
下面几个是经常用到的，要牢记
下面几个也重要，
还有很多其他奇奇怪怪的图标不用去记
下面这几个要记住place , transition 和arc
• Petri Nets consist of places and transitions
• Places can be input/output of transitions
• Places represent states, transitions represent state changes
• Places are represented by circles, transitions by thick bars
• Formally a Petri net N is a triple (P, T, F) where
– P is a finite set of places
– T is a finite set of transitions
– F (P x T T x P) is the flow relation
• p = {t T | (p, t) F}, p = {t T | (t, p) F},
etc
点的位置代表了前或者后，这里t看上去是一个实心的黑色宽竖线，但是其实就是transition
然后在此基础上加入了token的概念，圆圈里的那个黑色实心点，有了足够的token才可以进行下一步
• Transitions may change a marking by firing.
• Only enabled transitions may fire.
• Informally, a transition is enabled if each of its input places contains at least one token.
• Formally, a transition t is enabled in a marking M iff for each p, with p •t, M(p) > 0. (see definition 2.7 of [DE95])
下面链接有很多类似的练习，
