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Lesson 6 Quality factors
ObjectiveExplain how an architect can determine qualitative requirements.

Architecture and Qualitative Requirements

An architect translates the concerns of stakeholders into requirements by identifying the "quality factors" valued by each constituency. You have probably experienced quality factors yourself when using a system.
  1. Is the system reliable?
  2. Is it fast?
  3. How many concurrent users can the system handle before response time drops off?
  4. What makes a system good or good enough?
  5. Who is asking?

Separation of concerns

Quality Definition Factor
These quality factors ultimately translate into quantitative requirements. They are the performance metrics by which the solution is evaluated. The architect must manage trade-offs between ideal quality requirements and other factors such as schedule, cost, or feasibility.

Graphics versus performance
For example, high availability is a quality factor often sacrificed to cost and schedule considerations. Achievement of 99.99 percent availability usually presents a cost burden few organizations are willing to bear. But 99.5 percent availability may be good enough. Architects can explain the impact of these alternatives on the business. They can also determine whether the investment to achieve the higher availability is cost-justified.

As mentioned earlier, "The extra effort and expense associated with architecture almost always results in lower downstream operation costs." By identifying quality factors up front, the architect prevents conflicts later on— conflicts which often result in re-design, delays, and a potentially unhappy client/customer. It is often difficult to determine quality factors, for the following reasons:
  1. Quality is a moving target. In e-Business the bar is raised weekly, sometimes daily.
    Are we adding new products and services as quickly as we can?
  2. Some quality factors are unique to e-Business.
    How secure does it need to be? What is the penetration risk?
  3. Some quality factors are not very intuitive.
    Is your portal site similar to Yahoo, AOL, MSNBC?

The architect articulates a common vision based on the quality factors important to each stakeholder. In so doing, she provides some insurance against the evolutionary nature of the e-Business world.