There is a long list of Web technologies that we do not discuss in this book. This is mainly because this book is already loaded with good information, and some of the popular technologies are not strictly Open Source. Here we mention some of the omitted technologies ”things that are important to know ”but you need to look elsewhere for discussions about them.
XML Extensible Markup Language ”the future of the Web, according to many in the industry. XML will one day replace HTML as the language used to create web pages.  XML is also widely used to represent and transmit data on the network.
 Although we want to note that HTML is not going anywhere for a while.
Java An object-oriented programming language used to create applets (programs executed within the browser) and stand-alone applications. Java has an extensive API that provides methods to create GUI applications, socket programs, and more. Included under the Java umbrella is JSP, or JavaServer Pages. Java isn't discussed in this book because it isn't part of LAMP, and it's really closer to C++ at heart, a programming language.