Quality Attributes, Requirements, and Architectural Styles

Overview

Let’s now discuss the importance of quality attributes in software architecture. Quality attributes (QAs) are measurable or testable properties of a software system that indicate how well it meets the needs of stakeholders. These attributes must be clear and objective, ensuring that requirements are well-defined and testable.

Architects play a vital role in translating quality attributes into concrete software structures and designs. They must choose architectural styles and design elements that align with the desired quality attributes. A checklist of common quality attributes includes performance, scalability, availability, security, and flexibility, but the significance of each attribute can vary from project to project.

Quality attributes

Recall the architecture meta-frame diagramArchitectureMetaFrame.

QAs are the most important parts from an architectural point of view. Scenarios and constraints are also important, and they are a part of deciding which architectural style would be best for a given scenario. For example, our application may map to an internet web application scenario, which has unique architecture solutions compared to a mobile client application.

An important point to note about a QA is that the property must be measurable or testable. For example, suppose a requirement is that the application must have a good user interface. However, what does that mean? “Good” is a very subjective term and may mean different things to different stakeholders. It all depends on perspective. Therefore, the requirements must be testable. A measurable functional requirement would be: “A user must be able to perform a certain task within four mouse clicks.”

Quality attributes are not only nonfunctional requirements of the system, but also include service-level agreements and other concerns as well. These are important attributes that should be considered, because they can make or break the system.