What's the difference between function security and data security?

Function security is a statement of what actions you can perform in which user interface pages.

Data security is a statement of what action can be taken against which data.

Function security controls access to user interfaces and actions needed to perform the tasks of a job. For example, a warehouse manager can manage inventory transactions. The Warehouse Manager role provisioned to the warehouse manager authorizes access to the functions required to manage inventory transactions.

Data security controls access to data. In this example, the warehouse manager for M1 Inventory Organization can manage inventory transactions in the M1 Inventory Organization. Objects are secured by the data security policies of the job role.

Both function and data are secured through role-based access control.