Here is a wonderful documentation of three schema architecture of DBMS or Degrees of Data abstraction..
http://www.myreadingroom.co.in/images/stories/docs/dbms/degrees%20of%20data%20abstraction.pdf
Data Redundancy means same information is duplicated in several files. This makes data redundancy. (2) Data Inconsistency
Data Inconsistency means different copies of the same data are not matching. That means different versions of same basic data are existing. This occurs as