ZEND PHP 5 Certification STUDY GUIDE

188 ” XML and Web Services
structure of a document, which may not even be a requirement for your particular
needs. However, all XML documents must be well-formed for PHP’s XML functionality
to properly parse them, as XML itself is a strict language.
Creating an XML Document
Unless you are working with a DTD or XML Schema Definition (XSD), which provides
an alternate method to describe a document, creating XML is a free-form process,
without any rigid constraints except those that define a well-formed document. The
names of tags, attributes, and the order in which they appear are all up to the creator
of the XML document.
First and foremost, XML is a language that provides the means for describing data.
Each tag and attribute should consist of a descriptive name for the data contained
within it. For example, in XHTML, the tag is used to describe paragraph data,
while the tag describes table data and the tag describes data that is to be
emphasized. In the early days of HTML and text-based Web browsers, HTML tags
were intended merely to describe data, but, as Web browsers became more sophisticated,
HTML was used more for layout and display than as a markup language. For
this reason, HTML was reformulated as an application of XML in the form of XHTML.
While many continue to use XHTML as a layout language, its main purpose is to describe
types of data. Cascading style sheets (CSS) are now the preferred method for
defining the layout of XHTML documents.
Since the purpose of XML is to describe data, it lends itself well to the transportation
of data between disparate systems. There is no need for any of the systems
that are parties to a data exchange to share the same software packages, or encoding
mechanisms, or byte order. As long as both systems know how to read and parse
XML, they can talk. To understand how to create an XML document, we will be discussing
one such system that stores information about books. For the data, we have
plucked five random books from our bookshelf. Here they are:
Licensed to 482634 - Amber Barrow (itsadmin@deakin.edu.au)