PHP Programming for Windows (Landmark (New Riders))

XML is a language for creating metadata. Metadata is data that describes itself. To explain this further, let's look at a sample XML document:

<?xml version="1.0" encoding="UTF-8"?> <PEOPLE> <PERSON> <NAME>Andrew</NAME> </PERSON> </PEOPLE>

Don't worry if you have never encountered XML. I will explain how XML is made up later in this chapter. In this example, the data is a name: Andrew. Using XML, you can turn Andrew into metadata by describing it as a NAME :

<NAME>Andrew</NAME>

Each NAME belongs to a PERSON , which in turn belongs to PEOPLE . You can have multiple items of data that are all names , and you can describe them as such using the same method:

<?xml version="1.0" encoding="UTF-8"?> <PEOPLE> <PERSON> <NAME>Andrew</NAME> </PERSON> <PERSON> <NAME>Emma</NAME> </PERSON> <PERSON> <NAME>Terry</NAME> </PERSON> <PERSON> <NAME>Mary</NAME> </PERSON> <PERSON> <NAME>Thomas</NAME> </PEOPLE> </PERSON>

The elements that make up XML documents are called nodes . The sample XML document has the following nodes:

<NAME></NAME> <PERSON></PERSON> <PEOPLE></PEOPLE>

The most interesting thing to note about this example is that I made it up. XML is not really a language as such but a method that lets you create your own markup languages to then create metadata. You might have seen markup languages before; HTML is perhaps the most common markup language. (A version of HTML developed in XML is called XHTML.)