Database Reference
In-Depth Information
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Many classes are scheduled in one semester.
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Multiple classes can be scheduled on one weekday.
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Diferent classes can be scheduled for the same time block but in diferent classrooms.
From the Transcript, we can obtain the following rules:
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A grade is speciied by student ID, semester, and course. Since both semester and course are
included in the class information, the student ID and class ID together can be used to ind
a student's grade from a class.
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Each student can enroll in more than one class. As seen in the sample transcript, Liz enrolled
in two classes in fall 2008. By the university' rule, a student can take as many as 21 credit-
hour classes per semester.
So far, we have carefully analyzed the results from the interviews, the observation of the reg-
istration process, and the examination of the documents. he next step is to logically present the
class registration process. his task will be accomplished in the next section.
2.3 Entity-Relationship Data Model
From the above analysis, we have found that the registration oice wants to store the informa-
tion of the objects student, class, course, timeblock, weekday, semester, classroom, building, and
faculty. Before you can physically build a database to store the information, you should irst draw
a sketch, also called data model, to represent the database. It is similar to irst drawing a blueprint
of a house before you can physically build it. A data model consists of logical representations of
the objects and the relationships among these objects. You can use the data model to verify that
the new database will meet the business requirements. If changes on the database structure are
needed, it is much easier to do it on the data model. Once a database is built and populated with
data, it is much harder to make any change on the database structure.
Since the 1970s, several data modeling tools have been developed. One of the widely used
modeling tools is the entity-relationship model (E-R model) introduced by Peter Chen in 1976.
he E-R data model consists of entities, attributes, and relationships to represent the logical struc-
ture of a database. Another widely used modeling tool is uniied modeling language (UML),
which includes components such as classes, attributes, and operations.
2.3.1 Integration Deinition for Information Modeling
Before we develop an E-R data model, we will irst become familiar with the components of the
E-R model. An E-R model can be represented by several ways. One of the commonly used E-R
model representations is the
Integration Deinition for Information Modeling (IDEF1X)
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which is based on the national standard called Federal Information Standard published in 1993
due to the following advantages:
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E-R model components such as entities, attributes, relationships, and domains can be rep-
resented by the icons provided by IDEF1X.
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he IDEF1X standard can be used to represent most of the logical structures in a data
model.
