PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

810 Chapter 33 Connecting to Web Services with XML and SOAP
Listing 33.1
Continued
0596005431
Web Database Applications with PHP & MySQL,
2nd Edition
The document begins with the following line:
This standard declaration tells you the following document will be XML using UTF-8
character encoding.
Now look at the body of the document.The whole document consists of pairs of
opening and closing tags, such as what you see between the opening and closing Item
tags:
...
Item is an element, just as it would be in HTML. And, just as in HTML, you
can nest elements, such as this example of the ItemAttributes element, within the Item
element, which also has elements within it such as the Author element:
Luke Welling
Laura Thomson
Sams
Book
PHP and MySQL Web Development
There are also some differences from HTML.The first is that each opening tag must
have a closing tag.The exception to this rule is empty elements that open and close in a
single tag because they do not enclose any text. If you are familiar with XHTML, you
have seen the tag used in place of for this exact reason. In addition, all elements
must be properly nested.You would probably get away with Text
using an HTML parser, but to be valid XML or XHTML, the tags would need to be
properly nested as Text.
The main difference you will notice between XML and HTML is that we seem to be
making up our own tags as we go along! This is the flexibility of XML.You can structure
your documents to match the data that you want to store.You can formalize the
structure of XML documents by writing either a Document Type Definition (DTD) or
an XML Schema. Both of these documents are used to describe the structure of a given