The Physical Model

The Physical Data Model represents the database as it is. Typically, the physical data model might be represented as a series of SQL definitions and the operational processing model as structured English, along with equivalent SQL queries to the database.

It can be imported from a Database. It's the implementation. For a given Conceptual Model there can have several differents implementation and so Physical Data Model. More like this for a given problem there can have many different Conceptual Model.

The Data Dictionary

P, indicate that the column is a primary Key (it consequently indicate it's unicity)

R, indicate that the column is required

A, indicate that the column have to auto-increment

I, indicate that the column have to be indexed

Note that Merise require all columns name to be distinct