This paper examines use case diagrams as a visual tool for capturing dynamic relationships within systems and presenting requirements from multiple stakeholder perspectives. Using the process of purchasing prescription glasses as a detailed example, the paper illustrates how use case diagrams represent interactions among actors (patients, doctors, optical dispensaries) and the system itself. The paper distinguishes use case diagrams from activity diagrams, explaining how both diagram types complement each other in presentations: activity diagrams break down specific process steps while use case diagrams provide an overview of the entire system. Proper application of these visualization techniques enhances audience comprehension and enables clearer communication of complex processes.
Using diagrams in reports and presentations can greatly help convey the intended message more easily to the target audience. The visual aspect provided by diagrams allows audiences to relate better to whatever the speaker is trying to communicate. While presenting an idea without a diagram is still a viable approach, it requires significantly more focus from the audience to fully understand the message. Without visual aids, audience members must rely on their imagination to picture what is being presented. The real challenge, then, is choosing the right type of diagram for your specific purpose.
Many types of diagrams exist for different purposes. This paper focuses on one specific type that is primarily used in showing and capturing dynamic relationships within a system: the use case diagram. However, it is necessary to clarify the definition of a use case diagram since it shares similarities with other diagram types. To do this effectively, this paper will also present the activity diagram, another visual representation tool, to highlight the differences and complementary strengths of each approach.
By definition, a use case diagram is primarily used to capture the idea of relationships within a system. It presents the flow of activities by showing how two or more parties interact with each other. To create an effective use case diagram, requirements must be gathered not only from within the system but also from outside it. This comprehensive approach ensures that all influences on the system are represented, leading to a clear definition of the entire process.
In a use case diagram, actors are given specific roles to represent different parties that could affect the system being presented. Each actor then interacts through the diagram in a way that reflects how those parties relate to each other in real life. A straightforward example is the process of purchasing prescription glasses. In this scenario, the process involves three distinct actors: the patient, the doctor (optometrist or ophthalmologist), and the optical dispensary staff.
Understanding the distinctions between different eye care professionals is essential to this example. An optometrist performs eye exams and prescribes corrective lenses, while an ophthalmologist is a medical doctor with additional specialized training in eye care. According to the American Academy of Ophthalmology (2011), ophthalmologists have far more extensive educational backgrounds and are licensed medical doctors. Either way, both professionals should be able to give the correct prescription and recommendation if the patient needs glasses or requires a higher level of medical attention.
To illustrate how use case diagrams work, let us follow the complete process of purchasing prescription glasses from the patient's perspective. The process begins when a patient needs to determine whether he or she actually needs prescription glasses. To acquire this knowledge, a consultation with an optometrist must be scheduled. However, for more serious cases, the patient might need to consult with an ophthalmologist instead.
During the consultation, the patient's medical history will be reviewed. This step is critical because it helps trace any possible causes that might have affected the patient's eyesight. It is strongly recommended that patients exercise complete honesty during this part of the process, since every bit of information could lead to a more accurate diagnosis and appropriate treatment plan.
After the diagnosis is completed, a prescription for glasses will finally be given by the medical professional. If this is the patient's first time being diagnosed, the optometrist or ophthalmologist should recommend an optical dispensary where the patient can order glasses. In many cases, however, the hospital or clinic where the professional practices is already equipped with its own optical dispensary. When this is the case, the patient faces fewer obstacles in acquiring the new set of glasses.
Once the patient acquires the prescription, he or she can visit the recommended optical dispensary. At this point, the patient has the opportunity to select the frame for the glasses that were prescribed. An optician, who is trained to fit frames, will help with frame selection and will install the prescribed lenses or any other devices that were previously prescribed. It is important to note, however, that while opticians are trained to handle eye care devices, they are never allowed to change the diagnosis or replace the prescribed lenses (American Academy of Ophthalmology, 2011).
The patient then selects the desired frame and has it fitted according to the size best suited for his or her face. This step represents the extent of freedom a patient has in choosing how the glasses will look. The frames can be changed at will during this step, but the prescribed lenses must never be changed. The patient can then place the order for the glasses to be made. Depending on the frame type and manufacturing time, the glasses may take anywhere from a few hours to a week to complete.
When the scheduled release date arrives, the patient returns to the optical dispensary to try on the glasses and verify they meet expectations. The term "fitting" at this stage denotes two distinct meanings. First, fitting refers to the comfort and size of the frame and its effects on the wearer. Second, fitting ensures that the lenses attached to the frame are correct based on the prescription given by the optometrist or ophthalmologist during the initial consultation.
If the glasses satisfy both fitting criteria, payment can proceed. Depending on the optical dispensary's payment procedures, this payment could be the remaining balance owed or the full amount.
However, if the delivered glasses do not meet either of the two fitting categories mentioned above, payment should not yet be processed. It is necessary to reorder the glasses to ensure the patient receives the correct specifications. The patient must then wait again, as the glasses will be remade and similar waiting times may apply as in previous steps.
The use case diagram representing this entire process would show all three actors (patient, doctor, and optical dispensary) and the various interactions between them. It is important to note that this diagram is presented from the patient's perspective. A different use case diagram would be created if the perspective were changed to that of the doctor or the optical dispensary, as each stakeholder's view of the system interactions differs.
While use case diagrams show overall system interactions, activity diagrams focus on presenting a specific set of steps within the system. To represent the whole system using activity diagrams, a series of connected activity diagrams must be created.
In creating an activity diagram, the perspective being used is presented as the starting point of the diagram, and the end of the specific set of steps is presented as the conclusion of the diagram. Other parties involved appear as part of the process that the main actor must navigate.
If the same glasses purchase scenario is applied, three activity diagrams can be created: one for the consultation phase, one for the ordering phase, and one for the fitting and payment phase. In these diagrams, the patient serves as the starting actor in each, and each conclusion can technically serve as the starting point of the succeeding diagram. The doctor and optical dispensary are presented as parts of the process that the patient needs to follow.
Unlike the use case diagram, which provides a birds-eye view of system interactions, activity diagrams zoom in on the sequential steps and decision points within each phase. This level of detail makes activity diagrams particularly useful when you need your audience to follow specific procedures or understand the order of operations.
The difference between these two types of diagrams is clearly evident when both are applied to the same scenario. It is important to note, however, that both can be utilized to complement each other and amplify their respective effects.
A use case diagram captures the relationships and interactions between actors and the system as a whole. It answers the question: "Who participates in this system, and what are their roles?" Conversely, an activity diagram captures the sequence of steps and decision points within a specific process. It answers the question: "What happens at each stage, and in what order?"
"Distinctions and complementary strengths"
"Strategic sequencing for audience learning"
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