Monday, May 14, 2012

Oracle Introduction || Models Of DBMS

What  is Database?
                A Database is an Organized Collection of information/Data stored at the particular place written in pre-determined manner belongs to a particular topic, so as for easy retrieval .

What is DBMS?
                It is a software which is present inside the database can maintain and manage the data within the database.

Role of DBMS?

Models of DBMS?
                    Databases appeared in the late 1960s, at a time when the need for a flexible information management system had arisen. There are five models of DBMS, which are distinguished based on how they represent the data contained:

1)File Management System(FMS/FDBMS)
2)Hierarchical Management System(HMS/HDBMS)
3)Network DBMS
4)Relatioanl DBMS
5)Object Oriented DBMS

1)File Management System:
                This was the first model released in the market at 1960’s.In this model data is always stored in the form of a sequential manner (or) a continuous stream of characters.
Drawback :
           The main drawback of this model is if you want to locate (search) any particular value then user need to start searching from the beginning of the file, so it leads to increase the searching time.  

The hierarchical Model:
            This model was developed by IBM in 1968 when they are developing the project name is IMS(Information Management System).This model was developed on the basis of an O.S called MS.DOS.
            The data is sorted hierarchically, using a downward tree. This model uses pointers to navigate between stored data. 

The hierarchical model
1)Only one person can share the database at a time
2)If we want to add one more entry level between the existing levels then the user has to reconstruct entire tree structure.So,it is very tedious process and time taking process.  

The Network Model:
                   This model was developed by IBM in 1969 when they are developing the project name is IMS(Information Management System).This model was developed on the basis of an O.S called MULTICS(Multiplex Information Computing System).
                     like the hierarchical model, this model uses pointers toward stored data. However, it does not necessarily use a downward tree structure.   
The network model
     1)There is no proper Security for the centralized database.
     2) Redundancy of the database will be increased.
   3)It increases the lot of space and it leads to decrease the System performance and increases the inconsistency.

The Relational Model (RDBMSRelational database management system):  
             A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by a German scientist called E. F. Codd. Most popular databases currently in use are based on the relational database model.
              A short definition of an RDBMS is: a DBMS in which data is stored in tables and the relationships among the data are also stored in tables. The data can be accessed or reassembled in many different ways without having to change the table forms.

The object model (ODBMS, object-oriented database management system): 
                     The data is stored in the form of objects, which are structures called classes that display the data within. The fields are instances of these classes
ODBMS - Object-oriented database management system
By the late 1990s, relational databases were the most commonly used (comprising about three-quarters of all databases).

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