Technologically, the mashup phenomenon could not have happened without website owners making a clean separation between the data that is used on their sites, and the actual presentation of the data. This has always been a goal in computer application development, and therefore, it is no surprise that website and web application architecture have progressed towards this stage ever since the World Wide Web was created. This separation is quickly turning the World Wide Web into what is known as the semantic web—a philosophy where web content is presented not only for humans to read, but also in a way that can be easily processed by software and machines. We have moved from static pages to database-driven sites, from presentational FONT tags to cascading style sheets. It is perhaps inevitable that the web has become an environment that fosters mashup development.

Data sources of mashups are varied. Often, data owners provide mashup developers access to their data through official application programming interfaces. As we are talking about web applications, these APIs utilize web services, which come in a variety of protocols. Really Simple Syndication (RSS), a family of formats to present data, is another common data source that has helped spur the mashup adoption. When official methods are unavailable, developers become really creative in getting data. Screen scraping is a method that has always been around. Regardless of the method, mashups also deal with a variety of data formats. While mashups can be simple to create, a mashup developer must be flexible and well-rounded in the knowledge of their tools.

Open-source software is particularly well-suited in this mashup environment. The Apache and PHP combination makes for fast development. Being open source, developers are constantly and quickly adding new features to keep up with the web service world.

This book will take a look at how to use common data sources with PHP. Most official APIs are based on the big three web service protocols—XML-RPC, REST, and SOAP. We will of course look at these protocols. APIs and raw web service requests by hand, of course, are not the only way to retrieve data. We will look at using third-party libraries to interface with some popular sites. Feeds are also an important data source which we will use. By giving you a broad overview of the tools used in the mashup world, you should be able to start developing your own mashups quickly.