This chapter covered an important technology that you might need to use from within your web applications: XML Web Services. We have spent a lot of time and energy understanding how they work and of which component technologies they consist. With all of this information, we are able to easily write clients to work with Web Services and invoke their methods.
Some large corporations on the Internet offer functionality via XML Web Services, including Google (http://www.google.com/apis), Amazon.com Web Services (AWS), and a number of other services for weather and stock quoting.
In the next chapter, we look at PEAR, the PHP Extension and Application Repository, an excellent source of classes and functions for use within PHP.