To read and update - create and manipulate - an XML document, you will need an XML parser.
There are two basic types of XML parsers:
- Tree-based parser: This parser transforms an XML document into a tree structure. It analyzes the whole document, and provides access to the tree elements. e.g. the Document Object Model (DOM)
- Event-based parser: Views an XML document as a series of events. When a specific event occurs, it calls a function to handle it
The Expat parser is an event-based parser.
Event-based parsers focus on the content of the XML documents, not their structure. Because of this, event-based parsers can access data faster than tree-based parsers.
Look at the following XML fraction:
An event-based parser reports the XML above as a series of three events:
- Start element: from
- Start CDATA section, value: Jani
- Close element: from
The XML example above contains well-formed XML. However, the example is not valid XML, because there is no Document Type Definition (DTD) associated with it.
However, this makes no difference when using the Expat parser. Expat is a non-validating parser, and ignores any DTDs.
As an event-based, non-validating XML parser, Expat is fast and small, and a perfect match for PHP web applications.
Note: XML documents must be well-formed or Expat will generate an error.