AJAX is hot, hot, hot! Why? It's simple. With AJAX, internet developers and designers can create web-based applications that look and feel like desktop applications. These are responsive, highly-interactive applications that represent a new breed called "Rich Internet Applications" (RIA). This book is a guide to designing, implementing, and debugging AJAX applications. The book begins by comparing and contrasting the traditional web application lifecycle with that of an AJAX application. It then covers core AJAX technology, including the XMLHTTPRequest object, and describes various methods for "consuming" data returned by it. Because AJAX represents a fundamentally new way of creating web applications, the book is careful to explore usability guidelines for AJAX developers. This is followed by a series of use cases that show how specific problems are solved in both the pre-AJAX and post-AJAX worlds. The book ends with a chapter on debugging AJAX applications, along with appendices that cover toolkits that greatly simplify AJAX development. All of the server-side examples presented in the book will be written in PHP, the most popular langauage for server-side web programming.