Example 2: XML Attributes

How to add metadata to an element without creating more child elements

🎯 What does this example cover?

The same piece of data can be modeled as a child element or as an attribute. This example lets you build a <producto> and see the difference live: id, categoria and moneda are stored as attributes (inside the opening tag itself), while precio is stored as a child element, so you can compare both approaches in the same document.

Configure the product

Generated XML

ℹ️ Notice id, categoria y moneda están dentro de <producto ...>. Precio, en cambio, es un elemento completo aparte. 
<?xml version="1.0"?>
<producto id="045" categoria="ropa-deportiva" moneda="EUR">Camiseta t&#xE9;cnica<precio>19.95</precio></producto>

📖 Code Explanation

Complete PHP Code

<?php
$xml = new SimpleXMLElement('<producto/>');
$xml->addAttribute('id', $id);
$xml->addAttribute('categoria', $categoria);
$xml->addAttribute('moneda', $moneda);
$xml[0] = $nombre;                 // the node's text <producto>
$xml->addChild('precio', $precio); // child element
echo $xml->asXML();
?>

📝 addAttribute()

$xml->addAttribute('id', $id);

What does it do? Adds a name="value" pair inside the element's opening tag, without creating a new nested element.

💡 Concept: attribute vs. element

An attribute describes or identifies the element (metadata), while a child element usually represents its own data, substantial enough to have its own content and, potentially, its own sub-elements.

📝 The node's own text

$xml[0] = $nombre;

What does it do? Assigns the text content of the <producto> element (what goes between the opening and closing tags), instead of creating a new child.

📝 When to use each

Use attributes for identifiers, flags or short metadata (id, lang, moneda).

Use child elements when the data can have its own structure, be meaningfully empty, or need multiple values (several <etiqueta>, for example).

🎯 Key Concepts Learned

Attribute Syntax

  • They go inside the opening tag
  • Always in quotes: id="045"
  • An element can have several attributes

Attribute vs. Element

  • Attribute: simple, single metadata
  • Element: data with possible structure
  • There's no absolute rule, it's a design choice

SimpleXML

  • addAttribute() adds attributes
  • $nodo[0] = valor sets the node's text
  • addChild() still works for children

💪 Practical Exercise

Redesign the data model

  1. Change categoria from an attribute to a child element. Which line of code would you change?
  2. Add a new attribute stock with the available quantity
  3. Think of a case where the same data (for example, "date") would make sense as an attribute, and another where it would make more sense as an element

Categoría as a child element

// Antes: \$xml->addAttribute('categoria', \$categoria);
// Después:$xml->addChild('categoria', $categoria);

The result would be <categoria>ropa-deportiva</categoria> as a child of <producto>, instead of an attribute inside the tag.

New stock attribute

$xml->addAttribute('stock', '12');