PHP - XML Introduction

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With the help of PHP’s built-in functions and libraries, we can handle manipulation of XML data. XML, which stands for eXtensible Markup Language, is a data format for structured document interchange, especially on the Web.

XML is a popular file format used for serialization of data storing the data, transmitting it to another location, and reconstructing it at the destination.

In this chapter, we shall learn about the basics of XML processing with PHP.

Features of XML

One of the features of XML is that it is both human readable and machine readable. The specifications of XML are defined and standardized by The World Wide Web Consortium. PHP parser can perform read/write operations on XML data.

XML Tags

Like HTML, XML document is also composed with the help of tags. However, you can define your own tags, which is unlike HTML where you need to use predefined tags to compose a HTML document.

The HTML tags essentially apply formatting attributes over text, image, multimedia resources etc. The XML tags define user specified attributes to the data elements.

XML Document

An XML document has a hierarchical structure of tags that define the elements and attributes of data within a document. Each XML document consists of a root element that encloses other elements. Elements can have attributes, which provide additional information or properties about the element. The data within elements are enclosed by opening and closing tags.

Example

An example of a typical XML document is given below −

<?xml version = '1.0' encoding = 'UTF-8'?>   
<note>
   <Course>Android</Course>
   <Subject>Android</Subject>
   <Company>TutorialsPoint</Company>
   <Price>$10</Price>
</note>

Types of XML Parsers

In PHP, there are two types of XML parsers available −

• Tree based parsers

• Event based parsers

Tree-based Parsers

With this type of a parser, PHP loads the entire XML document in the memory and transforms the XML document into a Tree structure. It analyzes the whole document, and provides access to the Tree elements.

For smaller documents, tree-based parser works well, but for large XML document, it causes major performance issues. SimpleXML parser and DOM XML parser are the examples of tree-based parsers

Simple XML Parser

The Simple XML parser also called as tree-based XML parser and it will parse the simple XML file. Simple XML parse will call simplexml_load_file() method to get access to the xml from specific path.

DOM Parser

DOM Parser also called as a complex node parser, Which is used to parse highly complex XML file. It is used as interface to modify the XML file. DOM parser has encoded with UTF-8 character encoding.

Event-based Parsers

An event-based parser doesn’t load the entire XML document in the memory. instead, it reads in one node at a time. The parser allows you to interact with in real time. Once you move onto the next node, the old one is removed from the memory.

As there is no memory overload involved, this type of parser is suitable for large XML documents, and the document is parsed faster than any tree-based parser. XMLReader and XML Expat Parser are the examples of event-based parsers.

XML Parser

XML parsing is based on SAX parse. It is more faster the all above parsers. It will create the XML file and parse the XML. XML parser has encoded by ISO-8859-1, US-ASCII and UTF-8 character encoding.

XML Reader

XML Reader parse also called as Pull XML parse. It is used to read the XML file in a faster way. It works with high complex XML document with XML Validation.