Case Study

Table of Contents

Case Study Background

Course registration at the local university is currently done by hand. Students fill out forms that contain their course selections and return the forms to the registrar. Clerks then enter the selections into a database and a process is executed to create student schedules. The registration process takes from one to two weeks to complete.

The university decided to investigate the use of an online registration system. This system would be used by professors to indicate the courses they would teach, by students to select courses, and by the registrar to complete the registration process.

Course Registration System Problem Statement

At the beginning of each semester students may request a course catalogue containing a list of course offerings for the semester. Information about each course, such as professor, department, and prerequisites will be included to help students make informed decisions.

The new on-line registration system will allow students to select four course offerings for the coming semester. In addition, each student will indicate two alternative choices in case a course offering becomes filled or canceled. No course offering will have more than ten students. No course offering will have fewer than three students. A course offering with fewer than three students will be canceled. Once the registration process is completed for a student, the registration system sends information to the billing system, so the student can be billed for the semester.

Professors must be able to access the on-line system to indicate which courses they will be teaching. They will also need to see which students signed up for their course offering.

For each semester, there is a period of time that students can change their schedules. Students must be able to access the on-line system during this time to add or drop courses. The billing system will credit all students for courses dropped during this period of time.

The Role of Tools

Any software development method is best supported by a tool. This book uses the tool Rational Rose 4.0. Rational Rose is organized around the architectural views - use case, logical, component and deployment. This case study will map the steps of the process into the views contained in the tool.

Project Summary

This system will have a short inception phase during which prototyping is used to select the database. The use case diagram is started in the inception phase and matured in the elaboration phase. By the end of the elaboration phase, an architectural iteration is complete. The system is evolved in the construction phase in two iterations. The process components of requirements analysis, design, implementation and test are used in all phases of the project lifecycle.

The Inception Phase

Business Goals and Needs

The first question to address is the need for a new registration system. Does the University have the resources needed to design and implement the new system? In addition to the assessment of need for the system, the risks posed by the new system are elaborated. In the case of an on-line registration system, one of the major risks is the ability to store the information in a manner that is easily and quickly accessible by all.

For the purposes of this case study it was decided that the new system should be built. Prototypes were completed to address the database risks.

Definition of Actors

The following actors were defined for the problem:

Definition of Use Cases

The following use cases were elaborated for each actor:

Drawing a Use Case Diagram in Rational Rose

The use case diagram is contained within a class diagram in the use case view of the tool. Actors are shown as stickmen and use cases are shown as ovals. The use case diagram is shown in Figure 1.

Figure 1 Use Case Diagram

A brief description is created for each use case. The brief description is entered in the Documentation field of the use case specification in the tool. The brief description of each use case follows:

During Inception, the flow of events (including any identified alternate flows) for the most important use cases is documented.

In Rose 4.0, the flow of events is entered via a link to an external document. The flow of events for the Register for Courses use case is shown below.

Flow of Events: Register for Courses Use Case

This use case begins when the student enters the student id number. The system verifies that the student id number is valid and prompts the student to select the current semester or a future semester. The student enters the desired semester. The system prompts the student to select the desired activity:

The student indicates that the activity is complete. The system will print the student schedule and notify the student that registration is complete. The system sends billing information for the student to the billing system for processing.

Alternate flow

If an invalid id number is entered, the system will not allow access to the registration system.

If an attempt is made to create a schedule for a semester where a schedule already exists, the system will prompt for another choice to be made.

Create a Schedule

The student enters 4 primary course offering numbers and 2 alternate course offering numbers. The student then submits the request for courses. The system then:

  1. Checks that prerequisites are satisfied for the requested course.
  2. Adds the student to the course offering if the course offering is open.

Alternate flow

If a primary course offering is not available, the system will substitute an alternate course offering.

Review a Schedule

The student requests information on all course offerings in which the student is registered for a given semester. The system displays all courses for which the student is registered including course name, course number, course offering number, days of the week, time, location, and number of credit hours.

Change Schedule - Delete a Course

The student indicates which course offerings to delete. The system checks that the final date for changes has not been exceeded. The system deletes the student from the course offering. The system notifies the student that the request has been processed.

Change Schedule - Add a Course

The student indicates which course offerings to add. The system checks that the final date for changes has not been exceeded. The system then:

  1. Verifies that the maximum course load for the student has not been exceeded.
  2. Checks that prerequisites are satisfied for the requested course.
  3. Adds the student to the course offering if the course offering is open.

The Elaboration Phase

During Elaboration, some of the most important and critical use cases are implemented. During this phase, the focus is good class structure and architecture.

Development of Scenarios

Each use case is a web of scenarios. Scenarios are documented using Sequence Diagrams. Objects are represented as vertical lines and messages between objects are shown as directed horizontal lines. Sequence diagrams are drawn in the Use Case View of the tool. The Sequence Diagram for the Add a Course scenario is shown in Figure 2.

Figure 2 Sequence Diagram for the Add a Course Scenario

Creating "Real World" or "Business" Classes

Objects are discovered by examining the use cases and scenarios and grouped into classes. Each class should have a definition which states the purpose of the class. Packages are created to hold logical groups of classes. Classes and packages are drawn in the Logical View of the tool. The following packages and classes have been created for the registration system:

Class diagrams are created to graphically depict the packages and classes in the model. The Main class diagram typically contains only packages. Each package contains its own class diagrams. The Main class diagram for a package contains the public classes of the package (classes that communicate with classes in other packages). Other class diagrams are created as needed. Class diagrams are contained in the Logical View of the tool.

Use cases and scenarios are examined to determine the relationships needed by the system. Relationships between classes are created and displayed on selected class diagrams.

Attributes (structure) and operations (behavior) are added to the classes to carry out the functionality specified in the use cases.

Sequence diagrams are updated to show the allocation of objects to classes and the replacement of messages with operations.

Some class diagrams for the Registration System are shown in Figures 3 through 7. An updated sequence diagram is shown in Figure 8.

Figure 3 Main Class Diagram

Figure 4 Main Class Diagram for the People Package

Figure 5 Main Class Diagram for the University Artifacts Package

Figure 6 Course Reporting Class Diagram in the UniversityArtifacts Package

Figure 7 Main Class Diagram for the Interfaces Package

Figure 8 Updated Sequence Diagram

Software Architecture

As the elaboration phase of development continues, decisions concerning the architectural framework for the project are made. Scenarios are updated to show the interaction of the real world objects with the objects representing the architectural decisions. Packages and classes that carry out the architectural functionality are added to the logical view.

In the Course Registration system, the following architectural decisions were made:

The updated Main Class Diagram and an updated Sequence Diagram are shown in Figures 9 and 10.

Figure 9 Main Class Diagram

Figure 10 Updated Sequence Diagram

The next step is to implement a set of scenarios that address the major architectural issues. This is done to ensure early feedback and identification of problems. For this problem, the Maintain Curriculum Use Case was implemented since it addressed the major risk of this system--the database risk.

Iteration Planning

Another activity in the elaboration phase is the creation of the iteration plan. The goal of an iteration is to reduce risk in the system while incrementally building the final product. Use cases and scenarios are examined and prioritized to create the initial project plan. As each iteration is completed, risks are re-evaluated and the project plan is updated as needed.

For the Course Registration system the iteration plan is:

The Construction Phase

Construction Activities

During Construction, all remaining scenarios will be specified and implemented. At this time, many of the secondary scenarios are addressed.

Building an Iteration

This case study concentrates on the "Add a Course" scenario which is shown in Figure 14. During this phase of development, the classes that participate in the iteration are designed and implemented. Class diagrams are created to show the focus of the iteration.

For the Course Registration problem, the following design decisions are made:

An updated Sequence diagram showing the interaction with the added controller class is shown in Figure 11.

Figure 11 Updated Sequence Diagram

Add a Course

A package called Iteration 1 is added to the logical view of the model. Class diagrams showing the classes in the iteration are added to the package. A class diagram showing the design decisions made for the "Add a Course" scenario is shown in Figure 12.

Figure 12 Class Diagram "Add a Course"

The code for the iteration is completed and the iteration is tested and documented. The completed iteration is integrated with any previous iterations.

The Transition Phase

The system was successfully transitioned to the University community in two releases--beta and the final system. During the beta period, bugs were discovered, reported and fixed by the development staff. After using the beta version of the system, professors added the requirement to view a class roster on-line. This requirement was successfully implemented and available in the final release of the system. Students and professors were pleased with the time savings provided by the paperless system.

Due to the success of the Registration System it was decided that another version of the system should be developed to provide an on-line catalogue of course offerings. Budgets and staff were approved and the process began again.