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Web services expose data and operations over HTTP. They can range from simple websites serving static web pages, to major e-commerce platforms, and even portals into commercial data stores on the Web. Almost all modern-day software makes use of the Web in some way. Web services are especially critical for mobile apps because mobile devices are limited in both computing and storage capacity and often rely on web services for data processing and storage. Knowledge of network programming is essential for iOS developers and even people writing software for OS X.
A web service is a website or server that exposes data or operations over the Web, that is, via HTTP. This can simply be a service that exposes a few points of data, such as a website that publishes news articles, or a more complex system, such as an e-commerce platform that allows customers to search for items, buy goods, and track orders. The key is that these operations are exposed over HTTP, and thus work with any device capable of making a standard web (or