It all started with a friend. rel="friend" to be exact.
In 2003 at SXSW Interactive, Tantek Çelik proposed the use of rel="friend" for blogroll hyperlinks. About a year later, the nomenclature for structured data in HTML was born and dubbed "microformats." Microformats are HTML attributes that are added to existing elements. The attributes don't affect what people see when a Web page is rendered, but provide structured data to machines. What that means is that you can include contact details, events, reviews and other types of data, and search engines will be able to easily comprehend its meaning.
While structured data may be new to many search engine optimizers, it's actually been around for quite some time (at least in Internet years.) It's important to understand where structured data came from and where it's going, because it's poised to dramatically change how all sites communicate with search engines.
Creating the real Web 2.0
Let's go back to the early 2000s. The year after that SXSWi proposal, Tantek and his friends refined and developed different microformat standards, including XMDP, XFN, RelLicense, RelTag, RelNofollow, VoteLinks, XOXO, hCard, and hCalendar.
“I think what we're seeing is a stage of evolution which will have revolutionary impact.”
For those early leaders and others, microformats were about creating the semantic Web, what they referred to as the real Web 2.0. About two months later, on June 20, 2005, microformats.org launched as a central location for the structured data movement.
Adoption of Structured Data
Early adoption of microformats was very slow, supported mainly by Technorati and semantic enthusiasts. Google was an early adopter in 2005 with the infamousrel="nofollow." Yes, that's a microformat. It started to gain more traction and exposure after it was integrated into WordPress and other high-profile sites like Magnolia (now defunct.) E-commerce sites like Williams-Sonoma added the hProduct microformat to its product pages, and Yahoo! began using hCalendar for event pages on Upcoming.
But it wasn't until Google debuted Rich Snippets in May 2009 that structured data gained recognition. From that point on, it was only a matter of time until structured data would become a standard for communicating with machines, and in particular, search engines.
In late 2009, Google began testing a new kind of structured data called microdata. Microdata is a feature of HTML5 (now known as "Living Standard HTML".) Similar to microformats, microdata uses attributes inside of elements.
“At a high level, microdata consists of a group of name-value pairs. The groups are called items, and each name-value pair is a property. Items and properties are represented by regular elements.”
Microdata appears to be the grown-up and refined version of microformats. Think of it as more structured structured data. The key item attributes are "itemscope" and "itemprop," accompanied by supporting attributes like "itemid" and "itemref." With the exception of itemscope, all microdata attributes have values associated with them.
The appeal of microdata over microformats has to do with its tight integration into the living standard HTML and its ability to have values easily expanded. I have no doubt that this is the reason Google, Yahoo! and Bing chose this standard for their new structured data initiative, Schema.org.
Schema.org picks up where microformats left off. Schema types are hierarchical and can have multiples parents when expanded. There are currently two top-level types, "DataType" and "Thing." DataType includes sub-types, like dates, numbers and text. The Thing type is much more expansive and includes sub-types ranging from recipes to events. The full list of types is available at http://schema.org/docs/full.html.
Structured Data and SEO
Is structured data going to affect search engine result pages (SERPs)? Yes, and it already does.
Thanks to rich snippets — the use of microformats or RDFa markup — structured data already affects SERPs. Searching on Google for "beet salad" returns a list of beet salad reviews and recipes. You can even include and exclude ingredients to refine your search. All of this is possible because of rich snippets, and the top search results are dominated by sites that are using them.
Structured data allows search engine optimizers to provide explicit semantic meaning to their data. Coupled with structural elements from the living standard HTML — nav, aside, article, section, header and footer — SEOs have an entirely new arsenal for communicating content to search engines.
The beauty of adding structured data to Web pages is that it provides targeted exposure for your content. In the same way that Google appears to show preferencefor sites that utilize rich snippets, one can assume that the same will be true with microdata.
The use of structured data, like Schema.org's "types," will also go well beyond the reach of major search engines. Since it's an open format, expect to see innovators creating niche vertical search engines and services that primarily rely on microdata and other structured data formats.
The use of structured data has been a long time coming, and it's exciting to finally see it being widely adopted. SEOs should start to become very familiar with structured data formats like microformats and microdata if they haven't already. Otherwise, they'll risk becoming obsolete.
Jon Henshaw is product manager at Raven Internet Marketing Tools and a frequent PubCon speaker. You can read his full PubCon biography here.