How is data moved in and out of APO?

Do you know where I can find an APO implementation or development guide? I need to learn more about how data is moved in and out of APO. I understand that CIF is used for R/3 to APO and BAPIs are used for non-R/3 to R/3. Please advise.

The best way to find this is to go to the SAP help website (http://help.sap.com), once in the website click on "mySAP.com Cross-Industry Solutions" and then "SAP Advanced Planner & Optimiser". Now select the version and language that you want to use. A new window will appear and you need to select "APO - Advanced Planner and Optimiser" which is on the left hand side of the screen. Now click on the arrow-icon to the left of "Supply Chain Management (SCM) Business Scenarios" and you will see two sections, one on "Master Data" and one on "Integration of APO and R/3". These sections should give you an overview of how the data is transferred.