The use of goal graphs in goal oriented modeling allows us to make non-functional requirements explicit and make use of them in the design process. Using the goal graphs used in the NFR framework, it is possible to analyze goals that may compete with each other. Through this analysis, designers can make design decisions by evaluating the competing goals and their operationalizations. This analysis may also be used as a possible technique for taking the kind of holistic approach suggested by Kelly et al. (2004).
In the previous section, I have demonstrated a proposed technique for applying the reorganized guidelines with a sample interface. This reorganization of the guidelines allows us to bring the guidelines into a representation using the goal graphs, which opens up the opportunity for the analysis of these guidelines with other system goals. In this section, I shall demonstrate the method for this goal analysis and evaluation.
As mentioned earlier, system goals are often competing and they conflict with other goals. Consider the example of security as a system goal where the designers have chosen encryption as a technique for solving the security problem. But applying encryption technology will have some impact on the efficiency of a system since encryption technologies require additional computational power.
Let us consider a more relevant example, where the application of the reorganized accessibility guidelines can be seen. Consider that a small organization has a web site where they are planning to web-cast a live event. For this, they are using the following sample interface.
We are streaming the video live. Please stand by for the video to load
Figure VII.5: A sample interface for web-casting a live event
For making the sample interface above perceivable, the designer has to introduce the guideline number 1.2.3 from WCAG 2.0. This guideline is shown in figure VII.6. For
simplicity, I am considering only the specific portion of the guideline applicable in this scenario.
Figure VII.6: Goal for perceivable live contents
The guideline in figure VII.6 indicates that the designer is required to provide both open and closed captioning. It suggests that closed captioning be done using either SMIL 1.0 or 2.0, and any other readily available format with player. The applicable nodes of the goal graph have the pattern links.
Even though the organization is able to provide live web-cast of an event due to the minimal expenses required for web-casting the event, it cannot however afford to hire a web maintenance staff on a full-time basis for providing live captioning of the event. Furthermore, the organization has decided to reduce its expenses for operating the web site on a regular basis by performing web maintenance only when the staff are available. These constraints are indicated in the graph in figure VII.7.
Figure: VII.7: Cost limitations imposed on the web design
These considerations for the sample web contents can now be systematically analyzed together to check for the conflicts and consistency among the goals and the interface design. Figure VII.8 shows this interaction among the goal graphs and how it can be applied into the sample interface. Notice that even though the goals marked D, E, and F apply to the interface, goal F cannot be operationalized due to the constraints imposed by goal H. Since goal C refines into three mandatory goals using the AND link, all their operationalizations must be met before C can be satisficed. However, it can be seen that the situation still allows for the expertise to provide captioning in general. As it is not possible to provide captioned live synchronized media, goal F is denied from being implemented, and goals D and E are weakly denied from being implemented. Their evaluations are propagated to the goal C and above.
The goal evaluation and application showed in this case can also be considered a little differently by providing further refinement of goal marked B in figure VII.8. This has been done in figure VII.9 where the refinement of goal B is goal L. This goal indicates that by changing the needs of providing live captioned web-cast to a recorded media with captioning, it is still possible to achieve certain level of accessibility. It further indicates that goal L can be achieved with the current expertise of the organization’s web
maintenance staff.
Figure VII.8: Evaluation of the accessibility goals along with cost reduction goal
This example has considered a very simple situation by applying relevant goal graphs to make design decisions and evaluate them appropriately. The analysis provided in figure VII.9 indicates the difference in the outcome of the analysis than in figure VII.8. In figure VII.8 goal A has been weakly denied due to the system constraints, while in figure VII.9 the same goal has been weakly satisficed in an attempt to at least make the site contents more perceivable to the disabled users.
Figure VII.9: Satisficing the accessibility goals along with cost reduction goal using alternative techniques