Database Reference
In-Depth Information
Key Terms
artificial key
bottom-up design method
cardinality
category
complete category
composite entity
cumulative design
Database Design Language (DBDL)
dependent entity
entity-relationship (E-R) model
entity subtype
existence dependency
IDEF1X
identifying relationship
incomplete category
independent entity
information-level design
intelligent key
logical key
mandatory role
many-to-many relationship
many-to-many-to-many relationship
natural key
nonidentifying relationship
one-to-one relationship
optional role
physical-level design
secondary key
surrogate key
synthetic key
top-down design method
user view
weak entity
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Review Questions
1. Define the term user view as it applies to database design.
2. What is the purpose of breaking down the overall design problem into a consideration of individual user views?
3. Under what circumstances would you not need to break down an overall design into a consideration of individ-
ual user views?
4. The information-level design method presented in this chapter contains steps that must be repeated for each
user view. List the steps and briefly describe the kinds of activities that must take place at each step.
5. Describe the function of each of the following types of keys: primary, alternate, secondary, and foreign.
6. Suppose a given user view contains information about employees and projects. Suppose further each employee
has a unique EmployeeNum and each project has a unique ProjectNum. Explain how you would implement the
relationship between employees and projects in each of the following scenarios:
a. Many employees can work on a given project, but each employee can work on only a single project.
b. An employee can work on many projects, but each project has a unique employee assigned to it.
c. An employee can work on many projects, and a project can be worked on by many employees.
7. A database at a college is required to support the following requirements. Complete the information-level design
for this set of requirements. Use your own experience to determine any constraints you need that are not stated
in the problem. Represent the answer in DBDL.
a. For a department, store its number and name.
b. For an advisor, store his or her number and name and the number of the department to which he or she
is assigned.
c. For a course, store its code and description (for example, MTH110 or Algebra).
d. For a student, store his or her number and name. For each course the student has taken, store the
course code, course description, and grade received. In addition, store the number and name of the stu-
dent's advisor. Assume that an advisor may advise any number of students but that each student has
just one advisor.
8. List the changes you would need to make in your answer to Question 7 if a student could have more than one
advisor.
