Last week in my first article about Microdata I provided a brief introduction to the concept of Microdata and how it applies to a Joomla site. In discussion with other developers over the past week I'm surprised at how many people are unaware of this technology or just plain confused by it.

"I had no idea..." was the response of one when we were discussing the use of Microdata on an upcoming Joomla project. Another response was confusion over the difference between Structured Data, Microdata and Rich Snippets. Some blog posts and authorities on the subject refer to the use of Schema.

So, what's the difference?

"Structured Data" is the inclusion of structured name-value data pairs working in line with your content to help crawlers identify, classify and index your information.

The HTML5 Specification of structured data is called "Microdata". The Google Webmasters Tools page refers to it as Structured Data because Microdata is just one format for adding Structured Data to your markup. Other Stuctured Data formats supported by Google are Microformats and RDFa. Microdata is the format preferred by Google.

This is what Microdata looks like.

<div itemscope itemtype="http://schema.org/Recipe">
  <h1 itemprop="name">Nana's Linguini</h1>
  <img itemprop="photo" src="/blog/linguini.jpg" />
  <p>By <span itemprop="author">Catherine</span>, <span itemprop="published">November 5, 2013</span></p>
  ...

"Rich Snippets" are the short introductions Google displays under search results giving users a summary of your page. Finding Microdata within your page makes it easy for Google to create these Rich Snippets leading to better search results. Google can tell the difference between blogs, news, events, recipes, locations, movie reviews, etc. Even pulling relevant information like dates, times, images, ratings or nutritional information to display in the snippet when relevant to the users search.

Occasionally, Microdata is incorrectly called "Schema", referring to Schema.org which lays out the available type and property definitions. The Schema is the catalogue of definitions that you use within your Microdata declarations to define content types. In the code sample above, "name", "photo", "author" and "published", along with many others are part of the "Recipe" scope. Visit Schema.org for a full list of definitions.