XSL(T) can be used for organizing large trees of XML so that anyone can read it. For instance a Google Search Appliance serves up queries as XML. For that XML to be read by a general user some transformation has to occur. This is where XSL(T) plays a vital role. It could also be used to style an RSS feed page since the source is all in XML. It is also used as the main templating language for Autonomy's Teamsite (EMS) and such open source CMSs as Symphony.
Yahoo uses APIs for nearly all of its products. Instead of accessing a database and displaying the information live on the screen, the front end calls an API, which in turn gets the information from the back end, which talks to databases. This gives Yahoo the benefit of being able to scale to millions of users and being able to change either the front or back end without disrupting the other.
So what is YQL? YQL looks like SQL but enables you to access live data from the Internet. That definition doesn't really do it justice, however. The bigger point about YQL is that it includes many built-in bindings to various web APIs so that you can use almost every major web API in a consistent manner, with similar calls across the many possible APIs available to you.
This is a tutorial to explore the possibilities and the simplicity of our recently launched Tinypay API. With this API it is possible to add ecommerce functionalities to all kinds of applications in a few simple steps.