Beginning PHP 5.3

Chapter 19. Working with XML

XML — eXtensible Markup Language—lets you create text documents that can hold data in a structured way. It was originally designed to be a human-readable means of exchanging structured data, but it has also gained ground very quickly as a means of storing structured data. Although XML is different from a database in many ways, both XML and databases offer ways to format and store structured data, and both technologies have advantages and drawbacks.

XML isn't really a language but rather a specification for creating your own markup languages. It is a subset of Standard Generalized Markup Language (SGML, the parent of HTML). XML is intended to allow different applications to exchange data easily. If you're familiar with HTML, you'll notice similarities in the way HTML and XML documents are formatted. Although HTML has a fixed set of elements and attributes defined in the HTML specification, XML lets you create your own elements and attributes, thereby giving you the capability to define your own language in XML (or to use someone else's definition). Essentially, you can format any data you want using XML.

In addition, the definition of an XML-based language can be placed online for any person or application to read. So two applications that know nothing about each other can still exchange data as long as both applications have the ability to read and write XML.

For these reasons XML is rapidly becoming the data exchange standard, and many useful technologies ...