Blog (my web musings)

XML stands for EXtensible Markup Language. It is a language designed to accurately describe and structure data, keeping it separate from any styling or visual formatting. Its aim is to separate presentation, structure, and meaning from the actual content - and it does a pretty good job of it.

Storing the data in this fuss-free way is great and many tools, software and websites output data/feeds in the XML format because it is reliable, format-free, robust, easily transferred and easily manipulated - I'll be showing you how to manipulate it below using PHP's simpleXML extension, which is ready built-in to PHP5.

First, here's an example of an XML file for IT jobs that need doing around the office. The data is stored in self-descriptive tags that you can define yourself. That's right! You're not limited to using pre-defined elements as you are with HTML - with XML, you can make up your own (except for the first line -prolog- which describes the document as XML);

<?xml version="1.0" encoding="utf-8"?>
<tasks>
   <task date-added="2015-12-09">
       <title>Laptop Won't Boot</title>
       <message>Laptop gets to welcome screen then crashes. Blue screen of death.</message>
       <name>Toni</name>
       <priority>Emergency</priority>
       <status>OVERDUE</status>
   </task>
   <task date-added="2016-01-13">
       <title>Memory Card</title>
       <message>Corrupt memory card. Card-reader won't recognise it. Can't get pictures from it.</message>
       <name>Jim</name>
       <priority>Normal</priority>
       <status>OPEN</status>
   </task>
   <task date-added="2016-01-12">
       <title>Printer Cartridge</title>
       <message>New cartridge required for Kyocera printer. Black. High yield.</message>
       <name>Toni</name>
       <priority>High</priority>
       <status>OPEN</status>
   </task>
   <task date-added="2016-01-10">
       <title>Projector Bulb Orders</title>
       <message>Only 2 projector bulbs left in stock. Please order more.</message>
       <name>Carl</name>
       <priority>Normal</priority>
       <status>CLOSED</status>
   </task>
</tasks>

The XML file must contain one root element that is the parent of all other elements (<tasks>). Each item can then be nested within the parent (<task>).

This file is saved as 'tasks.xml'. Now begins the fun part - getting at the stored data and bending it to our will! Well, baby-steps first - let's start by simply outputting the bits we want to a web page...

Using simpleXML

First we have to load the XML file (which could also be a link to an online podcast or RSS news feed) into simpleXML;

<?php 

    $tasks = simplexml_load_file('path/to/tasks.xml'); // could also be an URL

?>

The $tasks variable now stores an array of mapped tags, that can be accessed like this...

The PHP code below prints the title, status and date-added attribute of the first task to the page (remember that arrays start from 0 in PHP, so the first task will be stored as task[0]);

<?php 

    $tasks = simplexml_load_file('path/to/tasks.xml'); // could also be an URL 
    echo $tasks -> task[0] -> title; 
    echo '<br/>'; 
    echo $tasks -> task[0] -> status; 
    echo '<br/>'; 
    echo $tasks -> task[0]['date-added'];

?>

Using a number reference is fine for targetting specific items, but what if you want to print a list of all the XML items? You can use a foreach loop;

<?php 

    $tasks = simplexml_load_file('path/to/tasks.xml'); // could also be an URL 
    echo '<ul id="tasks">'; 
    foreach ($tasks as $task) { // list all items 
        echo '<li>'; echo '<b>' . $task -> title . ': </b>' . $task -> message . ' <em><small>~ ' . $task -> name . '</small></em>'; 
        echo '<br/>'; 
        echo $task -> priority . ' | ' . $task -> status . ' (' . $tasks->task[0]['date-added'] . ')'; 
        echo '</li>'; 
        } 
    echo '</ul>';

?>

You can also limit the number of items displayed by using a for loop - this example displays only 3 items;

<?php 

    $tasks = simplexml_load_file('path/to/tasks.xml'); // could also be an URL 
    echo '<ul id="tasks">'; 
    for ($i = 0; $i < 3; $i++) { // list upto 3 items
        echo '<li>'; echo '<b>' . $task -> title . ': </b>' . $task -> message . ' <em><small>~ ' . $task -> name . '</small></em>'; 
        echo '<br/>'; 
        echo $task -> priority . ' | ' . $task -> status . ' (' . $tasks->task[0]['date-added'] . ')'; 
        echo '</li>'; 
        } 
    echo '</ul>';

?>

I hope you found this short introduction to XML, and XML manipulation with simpleXML useful.

I'll be expanding on this tutorial soon with a paginated RSS feed script.