Hi Tan Vu,
Looks like you are using JBPM5.4 and not JBPM 5.3 there. Thats why you do not have persistence.xml in your db folder.
unfortunately the current guide for jbpm5.4 still refers to the old file names
http://docs.jboss.org/jbpm/v5.4/userguide/ch.installer.html#d0e609
I wrote about changing db for jbpm5.4 but it was for ms sql server, maybe this can help you
https://community.jboss.org/wiki/SetUpJBPM54FinalInstallerToUseMSSQLServer2008UsingJTDS