Database Reference
In-Depth Information
◾
Data models compliant with the IDEF1X standard can be easily converted into a physical
database.
Because of these advantages, some popular database modeling software packages such as
ERwin and Microsoft Visio include IDEF1X as one of their data modeling standards. he IDEF1X
standard will be used for the development of the E-R model in this section. he following are the
descriptions of
entities
,
attributes
,
domains
,
relationships
, and
business rules
.
2.3.2 Entities
An entity is a generic name for an object such as a person, a computer, or a location involved in a
business process. In a class registration process, we are interested in keeping track of the informa-
tion about the objects such as class, student, course, faculty, semester, timeblock, weekday, build-
ing, and classroom. hese objects will be entities in the E-R model. According to the IDEF1X
standard, each entity can be represented by an icon as shown in Figure 2.3.
Graphically, an entity is represented by a rectangle with the entity name printed on top of
the rectangle in capital letters. he rectangle is divided into two parts. he top part is used to
display the identiier of the entity. he bottom part is used to display other attributes of the entity.
For the STUDENT entity, each individual student is an
instance
of the STUDENT entity. A
group of students is called an
entity class
. By the requirement analysis, the other possible entities
for this database project are CLASS, COURSE, CLASSROOM, BUILDING, TIMEBLOCK,
SEMESTER, and FACULTY.
2.3.3 Attributes, Identiiers, and Domains
Attributes are used to describe an entity. For the entity STUDENT, a student can be described
by his/her student ID, irst name, last name, and major, which are the attributes of the entity.
Figure 2.4 shows the IDEF1X icon for the entity STUDENT with its attributes.
As shown in Figure 2.4, the entity identiier StudentID is displayed in the top part of the rect-
angle, and other attributes are displayed in the lower part of the entity rectangle. As an identiier, a
STUDENT
Figure 2.3
IDEF1X icon representing an entity.
STUDENT
StudentID
FirstName
LastName
Major
Figure 2.4
IDEF1X icon representing entity STUDENT and its attributes.
