Hi,
See the below link for more information
https://docs-previous.pega.com/implementation-methodology-and-dco/understanding-class-structure-and-rulesets-generated-application-accelerator
https://docs-previous.pega.com/build-your-first-application

Thank You

Hi Anjan, 

I created a new application (Implementation only) on Pega 7.2.1 system. I saw 14 new classes created. See attached snapshots.

In my example:   new application name: "pscApp".  Organization layer: "PscO".

"PscO" is the top level class; "PscO-FW" is the base framework class; "PscO-Int" is the Organization Integration class; "PscO-Data" is the Organization Data Class; and etc ...

So, total 14 new classes were created. 

Thanks,

Susan