Many of you may have some concern on Basics of DBMS and about the definitions of R-DBMS, H-DBMS and N-DBMS. Some of you might have studied the concepts little different than the one I have defined on my site, but nevertheless definitions and concepts(DBMS) on my site are simple and easy to understand which are explained at a very basic level. Am collating some links which will provide similar and more detailed definitions and insight on DBMS concepts.
DBMS and its history -- http://en.wikipedia.org/wiki/Database_management_system
Types of DBMS -- http://en.wikipedia.org/wiki/Types_of_DBMS
Notes from Penn State University, USA -- http://www.personal.psu.edu/glh10/ist110/topic/topic07/topic07_06.html
Flat File Database -- http://en.wikipedia.org/wiki/Flat_file_database
Hierarchical DBMS -- http://en.wikipedia.org/wiki/Hierarchical_database_model
Network DBMS -- http://en.wikipedia.org/wiki/Network_model_(database)
Relational DBMS -- http://en.wikipedia.org/wiki/Relational_model
Database(Do not get confused with so much information, treat this link as a reference) -- http://en.wikipedia.org/wiki/Database
Hope this clears the confusion in air.