This iOS SDK is a client library to access the Square Point of Sale API. The Point of Sale API gives mobile applications the ability to open the Square Point of Sale application, to process in-person payments using Square hardware. It allows you to build customized point-of-sale solutions or other applications that require payments that includes support for native and web apps on iOS and Android to process in-person payments using Square hardware. Square enables developers with the ability to build customized solutions that accept payments online, in-person, or in-app. Square provides services to manage products and customers, that support products and tools to manage finances.
With respect to Web APIs, the industry has clearly and emphatically landed on REST as the standard way to implement these services. And for good reason... REST, which is generally implemented as a one-size-fits-all solution, is an excellent choice for a most companies who wish to expose their content to third parties, mobile app developers, partners, internal teams, etc. There are many tomes about what REST is and how best to implement it, so I won’t go into detail here. But if I were to sum up the value proposition to these companies of the traditional REST solution, I would describe it as: