子流程：SubProcess，CallActiviti的区别
https://community.alfresco.com/thread/221771-call-activiti-vs-subprocess
http://blog.sina.com.cn/s/blog_befb86ae0101cetg.html
http://www.oschina.net/question/54100_39418
BPM3教学视频
http://www.jee-soft.cn/htsite/html/cpjfw/zxjc/bpmx3/