1. List four significant differences between a file-processing system and a DBMS.
* A database management system coordinates both the physical and the logical access to the data, whereas a file-processing system coordinates only the physical access. * A database management system reduces the amount of data duplication by ensuring that a physical piece of data is available to all programs authorized to have access to it, whereas data written by one program in a file-processing system may not be readable by another program. * A database management system is designed to allow flexible access to data, whereas a file-processing system is designed to allow predetermined access to data. * A database management system is designed to coordinate multiple users accessing the same data at the same time. A file-processing system is usually designed to allow one or more programs to access different data files at the same time.
2. Explain the concept of physical data independence, and its importance in database systems.
The ability to modify a schema definition in one level without affecting a schema definition in the next higher level is called Data Independence. The ability to modify the physical schema without causing application programs to be rewritten or without changing the logical schema is called physical data independence.
Importance of data independence in database systems: * Improve performance * Change in data structure do not require change in application program. * Allow users to concentrate on the general structure, rather than on low-level implementation details. * Security can be improved. * Integrity can be improved. * Better service to the users. * Cost of developing and maintaining systems is lower. * Flexibility in system improvement. * Inconsistencies can be reduced.
