We have discussed the basics of how web services work, and we touched on how to use them, but we have not discussed what services are already available. After all, if you have defined a module in an application to fetch a certain bit of information, it would be better defined as a publicly available service, if possible. You do not want to reinvent the wheel if you do not have to.
To that end, publicly available web services have supplied developers with the APIs to their services to make it easier to use them. This is also helpful for getting "up and running" quickly, something that is important in today's world of rapid application deployment. It would be impossible, however, to go over all of the publicly available web services that exist today; new ones pop up all the time while old and obsolete ones disappear, and a service's interface could change over time to better reflect the needs of developers.
Instead, I will highlight some of the better known, well-documented, and more readily used web services to give you a leg up on beginning to develop with them. And though they may change, at least you'll have the foundation available to begin programming.
An important thing for a web developer to know is what services are out there and how to use them. Without this knowledge, you have to search the Internet for what you need and hope that you find it in a short amount of time. Otherwise, it is costing you or your employer—as ...