Hi Anoop,
Sorry for the delay.
In the current master branch, Activity Tasks and Notifications are created and managed by what is called the Task Management Process.
To make things easy, this process executes some requests to TMS, (mostly responsible for tasks persistence) and this creates entries in the DB.
Then the task list (UIFW) is making some request to retrieve the list of task for the logged in user. This requests then collects all the tasks and notification created by TMP.
PIPA (process tasks) can be found in the var/deploy folder, under files named *.pipa.
Those task descriptors are picked up by a TMS task loader, and are then created in the database, depending on the information found in this .pipa file.