CONTENTS:• DEFINATION• ADVANTAGES• DISADVANTAGES• THREE LEVEL OF ARCHITECTURE – EXTERNAL VIEW – CONCEPTUAL VIEW – INTERNAL VIEW
DBMS• DATA: Data is raw fact or figures or entity.• DATABASE: A database is an organized collection of facts. In other words we can say that it is collection of information arranged and presented to serve to a particular purpose.
Database Management System:Database management system (DBMS) is asoftware system that allows access to data contained in a database. The objective of the DBMS is to provide a convenient effective method of defining, storing and retrieving the information contained in a database.
ADVANTAGES:• Reduction of Redundancies:Centralized control of data by DBA avoids unnecessary duplication of data and effectively reduces the total amount of data storage required. It also eliminates the extra processing necessary to trace the required data in large mass of data.
• Shared Data: DBMS allows sharing of data under its control by any number of application programs or users.• Security:Different level of security could be implemented for various types of data and operation. The DBA who has the ultimate responsibility for the data in the DBMS can ensure that the proper access procedures are followed.
• Integrity:Centralized control can also ensure that adequate checks are incorporated in the DBMS to provide data integrity. Data integrity means that the data contained in the database is both accurate and consistent.
DISADVANTAGES:• A significant disadvantage of the DBMS is cost. In addition to the cost of purchasing or developing the software, the hardware has to be upgraded to allow for the extensive programs and the work spaces required for their execution and storage.• The processing overhead introduced by the DBMS to implement security, integrity and sharing of the data causes a degradation of the response and throughput time.
• While centralization reduces duplication, the lack of duplication requires that the database be adequately backed up , so that in the case of failure, the data can be recovered. Backup and Recovery operations are fairly complex in a DBMS environment.
THREE LEVELARCHITECTURES• DBMS provide user with an abstract view data i.e the system has certain details of how the data store and maintain. In DBMS, the data abstracted in three levels corresponding to three views are as: – External View – Conceptual View – Internal View
EXTERNAL VIEWThis is the highest level of database abstraction as seen by the user where only those portions of the database of concern to a user or application program are included. Any number of user views may exist for a given global or conceptual view.
CONCEPTUAL VIEWAt this level of database abstraction all the database entities and the relationship among them are included. One conceptual view can represents the entire database. It describes all the logical records and relationships in the conceptual view.
INTERNAL VIEWThis view is the lowest level of abstraction, closest to the physical storage method used. It indicates how the data stored and describes the data structures and access methods to be used by the database.