For all these reasons, database systems have become ubiquitous. As we will see, the use of database
systems has been facilitated, too, by a set of language standards called SQL. It is difficult to imagine any
substantial application today that does not include a database, or provide a direct link to an existing database.
MODELING THE DATA DOMAIN
Before creating a relational database, the designer goes through a process called data modeling.
The modeling phase identifies the ???entities??? which will be of interest, the ???attributes??? of each entity type, and
the ???relationships??? between different entity types.
140 DATABASE [CHAP. 8
For instance, in developing a database for a college, entity types would include students, professors,
dormitory buildings, classroom buildings, majors, courses, etc. Attributes of a student would include name,
address, dorm, room number, major, advisor, etc. One relationship between entity types would be the advisor/
advisee relationship between a professor and a student.
Entities are the ???things,??? the ???nouns,??? the database will store. Often entity types correspond to classes of
real-world objects, such as professors, cars, and buildings. Sometimes entity types correspond to more abstract
objects, like a college within a university, an order for an on-line bookstore, and a privilege afforded a group of
users.
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