Database Reference
In-Depth Information
Database layers of abstraction
Databases have the unique capability of presenting multiple users of the data with their own
distinct views of that data while storing the underlying data only once. These are collect-
ively called user views. Because views store no actual data, they automatically reflect any
data changes made to the underlying database objects. This is all possible through layers of
2.5.1 The Physical / Internal Layer
The physical layer contains the data files that hold all the data for the database. All modern
DBMSs allow the database to be stored in multiple data files, which are usually spread out
over multiple physical disk drives. Maximum performance can be achieved with this ar-
rangement. However, Microsoft Access noted DBMS, stores the entire database in a single
physical file. This arrangement limits the ability of the DBMS to scale to accommodate
many concurrent users of the database, making it inappropriate as a solution for large en-
terprise systems, while simplifying database use on a singleuser personal computer system.
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