http://edndoc.esri.com/arcobjects/9.2/net/63391c82-c2e6-4797-b2e6-2c1d92f56f44.htm
http://help.arcgis.com/en/sdk/10.0/Arcobjects_net/conceptualhelp/index.html#//0001000002n4000000
http://zhihu.esrichina.com.cn/question/12460