Software as a service (SaaS) and cloud computing are becoming increasingly popular as companies try to reduce the cost overheads associated with installing, upgrading, and maintaining deployed software. The result is a range of rich Internet services with which you can build thin mobile applications that enrich online services with the personalization available from your smartphone or tablet
The idea of using a middle tier to reduce client-side load is not a novel one, and happily there are many Internet-based options to supply your applications with the level of service you need.
Google Services APIs — In addition to the native Google applications, Google offers web APIs for access to their Calendar, Docs, Blogger, and Picasa Web Albums platforms. These APIs collectively make use of a form of XML for data communication.
Yahoo! Pipes — Yahoo! Pipes offers a graphical web-based approach to XML feed manipulation. Using pipes, you can fi lter, aggregate, analyze, and otherwise manipulate XML feeds and output them in a variety of formats to be consumed by your applications.
Google App Engine — Using the Google App Engine, you can create cloud-hosted web services that shift complex processing away from your mobile client. Doing so reduces the load on your system resources but comes at the price of Internet-connection dependency. Google also offers Cloud Storage and Prediction API services.
Amazon Web Services — Amazon offers a range of cloud-based services, including a rich API for accessing its media database of books, CDs, and DVDs. Amazon also offers a distributed storage solution (S3) and Elastic Compute Cloud (EC2)