Systems Analysis and Design

In my personal experience the most taxing part of performing analysis and design of a system is the mental load required to keep all components, requirements, and trade-offs front of mind. Especially in a larger system design the number of interconnected modules and requirements can be overwhelming to try to conceptualize all at once. Consistent documentation helps in being able to move things out of your head into a reference form but as an analyst you still need to keep an awful lot of moving parts in your head at the same time.

Throughout Chapter 4 of the Microsoft Application Architecture Guide the authors provide methods for taking specific representative examples of what the system will provide to analyze trade-offs and validate assumptions on a smaller scale. Within the section describing key scenarios, they are described as areas which are unknown or risky, and represent a place where a tradeoff might need to be made between qualities such as security vs. ease of use or user experience (2009).

Essentially the article suggests that the most siginificant use cases can stand in for every other use case for the purposes of evaluating candidate architecture, and I completely agree with that assessment. If you can spend time early identifying ten use cases which are representative of 90 others, you've reduced your work to review, test, and present for acceptance to a tenth of what it would be if you tried to enumerate and validate even an abbreviated version of each case.

Another consideration in favor of extracting and iterating on key scenarios is the ability to communicate good ones to your customer. Alexander highlights the usefulness of evocative scenarios to hold the attention of customers (2000), and limiting the number of scenarios for evaluation allows the system designer to focus more deeply on their action and impact on the system when communicating with stakeholders.

References

Alexander, I. (2000, October). Scenarios in systems engineering. Retrieved February 16, 2024, from https://www.scenarioplus.org.uk/papers/scenarios/intro_to_scenarios.htm

Microsoft Corporation. (2009). Microsoft Application Architecture Guide (2nd ed.). Microsoft Press. https://learn.microsoft.com/en-us/previous-versions/msp-n-p/ee658084(v=pandp.10)