A crucial question we need to know is in what technology the Sweater app should be built with. This selection will ideally depend on the design goals of the project and the “business” needs of the project. It may also depend on what the development team already knows and what kind of time budget there is for learning new technologies.

The potentially evolving design requirements for the project are discussed elsewhere. Some of the business needs one might need to consider are:

• How soon must the app ship?
• How important is it that features can be added?
• How important is it that the styling can be changed?

Based on the core concept of the app, some of the available technologies that seem suitable include

• The Webstack – including special libraries or frameworks or just plain HTML/CSS/JS.
• Android
• iOS

Other technologies like Kivy, Qt Quick, and even desktop-oriented frameworks could also be considered. But for this somewhat contrived example, I will limit our options to the list above. In addition, for the time being, I will decide, perhaps arbitrarily, to do an implementation using Web technologies. In the future, this might be accompanied by other implementations for completeness.

• Web implementation