Supporting usability in product line architectures.

This paper addresses the problem of supporting usability in the early stages of a product line architecture design. The product line used as an example is intended to support a variety of different products each with a radically different user interface. The development cycles for new products varies between three years and five years and usability is valued as an important quality attribute for each product in the line. Traditionally, usability is achieved in a product by designing according to specific usability guidelines, and then performing user tests. User interface design can be performed separately from software architecture design and prototyping, but user tests cannot be performed before detailed UI design and prototyping. If the user tests discover usability problems leading to required architectural changes, the company would not know about this until two years after the architecture design was complete. This problem was addressed by identifying a collection of 19 well known usability scenarios that require architectural support. In our example, the stakeholders for the product line prioritized three of these scenarios as key product-line scenarios for improving usability. For each of these three chosen product-line scenarios we developed an architectural responsibility pattern that provided support for the scenario. The responsibilities are expressed in terms of architectural requirements with implementation details and rationales. The responsibilities were embodied in a web based tool for the architects. The two architects for the product line developed a preliminary design and then reviewed their design against the responsibilities supporting the scenarios. The process of review took a day and the architects conservatively estimated that it saved them five weeks of effort later in the project.