What is the difference between logical data independence and physical data independence?

I have the definitions of each but was hoping maybe someone here could break it down for me a bit more because I'm not really grasping it.



This is what I have:



Logical data independence is the capacity to change the conceptual schema of a database system without having to change the schema at the view level. You only need to change external/conceptual mappings



Physical data independence is the capacity to change the internal schema of a database system without having to change the schema at the conceptual level

You only need to change conceptual/internal mappings .What is the difference between logical data independence and physical data independence?
Data independence is normally thought of in terms of two levels or types. Logical data independence makes it possible to change the structure of the data independently of modifying the applications or programs that make use of the data. There is no need to rewrite current applications as part of the process of adding to or removing data from then system.



The second type or level of data independence is known as physical data independence. This approach has to do with altering the organization or storage procedures related to the data, rather than modifying the data itself. Accomplishing this shift in file organization or the indexing strategy used for the data does not require any modification to the external structure of the applications, meaning that users of the applications are not likely to notice any difference at all in the function of their programs.