Fetching process data from PostgreSQL

I am using Bonita BPM Community Edition Version : 7.3.1 and PostgreSQL have three forms in my process.I want to use data which Bonita by default saves in its configured database. First form is starting process having fields like Title, Start Date, End Date, upload file widget. Second form is changing title, dates and files.Third form is is for only viewing these changes and finalize them. How can i get all these values after third form submission. How can i relate tables and get my variables values.