next up previous contents index
Next: Controlled access to data Up: Database Management Systems (DBMSs) Previous: Safe storage of data

Application-independent storage of data

Data held in a DBMS has a greater lifetime than the applications using the data. In fact, in most cases data will outlive the DBMS in which it is stored.

This means that data storage has to be organised independently of any application so that different applications (or generations of applications) can access the same data efficiently, and that import and export procedures have to be provided for the migration of data to new DBMSs.

In DBMSs, application independence is achieved by hiding the physical storage of data from the users. The DBMS automatically maps the storage requirements of a database schema to the file system of the operating system, creates a meta-schema which contains all information about the data stored in the DBMS and generates index files to speed up access to the data.

External applications cannot access data stored in a DBMS directly, e.g. by opening a file. On the one hand, this is a further security measure by which tampering with data is prevented, on the other hand this places the burden of determining efficient data storage organisation and optimising access to the data on the DBMS.

EAGLES SWLG SoftEdition, May 1997. Get the book...