The DBA can enforce this policy by giving students permission to read only the
Courseinfo view.
Data availability and recovery from failures: The DBA must take steps
to ensure that if the system fails, users can continue to access as much of the
uncorrupted data as possible. The DBA must also work to restore the data to a
consistent state. The DBMS provides software support for these functions, but the
DBA is responsible for implementing procedures to back up the data periodically
and to maintain logs of system activity (to facilitate recovery from a crash).
Database tuning: The needs of users are likely to evolve with time. The DBA is
responsible for modifying the database, in particular the conceptual and physical
schemas, to ensure adequate performance as user requirements change.
1.10 POINTS TO REVIEW
A database management system (DBMS) is software that supports management
of large collections of data. A DBMS provides efficient data access, data in-
dependence, data integrity, security, quick application development, support for
concurrent access, and recovery from system failures. (Section 1.1)
Storing data in a DBMS versus storing it in operating system files has many
advantages. (Section 1.3)
Using a DBMS provides the user with data independence, efficient data access,
automatic data integrity, and security. (Section 1.4)
The structure of the data is described in terms of a data model and the description
is called a schema. The relational model is currently the most popular data model.
A DBMS distinguishes between external, conceptual, and physical schema and
thus allows a view of the data at three levels of abstraction. Physical and 

PEOPLE WHO DEAL WITH DATABASES
Quite a variety of people are associated with the creation and use of databases. Obvi-
ously, there are database implementors, who build DBMS software, and end users
who wish to store and use data in a DBMS. Database implementors work for ven-
dors such as IBM or Oracle. End users come from a diverse and increasing number
of fields. As data grows in complexity and volume, and is increasingly recognized as
a major asset, the importance of maintaining it professionally in a DBMS is being
widely accepted. Many end users simply use applications written by database applica-
tion programmers (see below), and so require little technical knowledge about DBMS
software. Of course, sophisticated users who make more extensive use of a DBMS,
such as writing their own queries, require a deeper understanding of its features.
In addition to end users and implementors, two other classes of people are associated
with a DBMS: application programmers and database administrators (DBAs).
Database application programmers develop packages that facilitate data access
for end users, who are usually not computer professionals, using the host or data
languages and software tools that DBMS vendors provide. (Such tools include report
writers, spreadsheets, statistical packages, etc.) Application programs should ideally
access data through the external schema. It is possible to write applications that access
data at a lower level, but such applications would compromise data independence.
A personal database is typically maintained by the individual who owns it and uses it.
However, corporate or enterprise-wide databases are typically important enough and
complex enough that the task of designing and maintaining the database is entrusted
to a professional called the database administrator. The DBA is responsible for
many critical tasks:
Design of the conceptual and physical schemas: The DBA is responsible
for interacting with the users of the system to understand what data is to be
stored in the DBMS and how it is likely to be used. Based on this knowledge, the
DBA must design the conceptual schema (decide what relations to store) and the
physical schema (decide how to store them). The DBA may also design widely
used portions of the external schema, although users will probably augment this
schema by creating additional views.
Security and authorization: The DBA is responsible for ensuring that unau-
thorized data access is not permitted. In general, not everyone should be able
to access all the data. In a relational DBMS, users can be granted permission
to access only certain views and relations. For example, although you might al-
low students to find out course enrollments and who teaches a given course, you
would not want students to see faculty salaries or each others' grade information.