Mythical Differences: RDFa Lite vs. Microdata

Full disclosure: I’m the current chair of the standards group at the World Wide Web Consortium that created the newest version of RDFa.

RDFa 1.1 became an official Web specification last month. Google started supporting RDFa in Google Rich Snippets some time ago and has recently announced that they will support RDFa Lite for schema.org as well. These announcements have led to a weekly increase in the number of times the following question is asked by Web developers on Twitter and Google+:

“What should I implement on my website? Microdata or RDFa?”

This blog post attempts to answer the question once and for all. It dispels some of the myths around the Microdata vs. RDFa debate and outlines how the two languages evolved to solve the same problem in almost exactly the same way.

 

Here’s the short answer for those of you that don’t have the time to read this entire blog post: Use RDFa Lite – it does everything important that Microdata does, it’s an official standard, and has the strongest deployment of the two.

Functionally Equivalent

Microdata was initially designed as a simple subset of RDFa and Microformats, primarily focusing on the core features of RDFa. Unfortunately, when this was done, the choice was made to break compatibility with RDFa and effectively fork the specification. Conversely, RDFa Lite highlights the subset of RDFa that Microdata did, but does it in a way that does not break backwards compatibility with RDFa. This was done on purpose, so that Web developers wouldn’t have a hard decision in front of them.

RDFa Lite contains all of the simplicity of Microdata coupled with the extensibility of and compatibility with RDFa. This is an important point that is often lost in the debate – there is no solid technical reason for choosing Microdata over RDFa Lite anymore. There may have been a year ago, but RDFa Lite made a few tweaks in such a way as to achieve feature-parity with Microdata today while being able to do much more than Microdata if you ever need the flexibility. If you don’t want to code yourself into a corner – use RDFa Lite.

To examine why RDFa Lite is a better choice, let’s take a look at the markup attributes for Microdata and the functionally equivalent ones provided by RDFa Lite:

Microdata 1.0 RDFa Lite 1.1 Purpose
itemid resource Used to identify the exact thing that is being described using a URL, such as a specific person, event, or place.
itemprop property Used to identify a property of the thing being described, such as a name, date, or location.
itemscope not needed Used to signal that a new thing is being described.
itemtype typeof Used to identify the type of thing being described, such as a person, event, or place.
itemref not needed Used to copy-paste a piece of data and associate it with multiple things.
not supported vocab Used to specify a default vocabulary that contains terms that are used by markup.
not supported prefix Used to mix different vocabularies in the same document, like ones provided by Facebook, Google, and open source projects.

As you can see above, both languages have exactly the same number of attributes. There are nuanced differences on what each attribute allows one to do, but Web developers only need to remember one thing from this blog post: Over 99% of all Microdata markup in the wild can be expressed in RDFa Lite just as easily. This is a provable fact – replace all Microdata attributes with the equivalent RDFa Lite attributes, add vocab="http://schema.org/" to the markup block, and you’re done.

At this point, you may be asking yourself why the two languages are so similar. There is almost 8 years of history here, but to summarize: RDFa was created around the 2004 time frame, Microdata came much later and used RDFa as a design template. Microdata chose a subset of the original RDFa design to support, but did so in an incompatible way. RDFa Lite then highlighted the subset of the functionality that Microdata did, but in a way that is backwards compatible with RDFa. RDFa Lite did this while keeping the flexibility of the original RDFa intact.

That leaves us where we are today – with two languages, Microdata and RDFa Lite, that accomplish the same things using the same markup patterns. The reason both exist is a very long story involving politics, egos, and a fair amount of disfunctionality between various standards groups – all of which doesn’t have any impact on the actual functionality of either language. The bottom line is that we now have two languages that do almost exactly the same thing. One of them, RDFa Lite 1.1, is currently an official standard. The other one, Microdata, probably won’t become a standard until 2014.

Markup Similarity

The biggest deployment of Microdata on the Web is for implementing the schema.org vocabulary by Google. Recently, with the release of RDFa Lite 1.1, Google has announced their intent to “officially” support RDFa as well. To see what this means for Web developers, let’s take a look at some markup. Here is a side-by-side comparison of two markup examples – one in Microdata and another in RDFa Lite 1.1:

Microdata 1.0 RDFa Lite 1.1
<div itemscope itemtype="http://schema.org/Product">
  <img itemprop="image" src="dell-30in-lcd.jpg" />
  <span itemprop="name">Dell UltraSharp 30" LCD Monitor</span>
</div>
<div vocab="http://schema.org/" typeof="Product">
  <img property="image" src="dell-30in-lcd.jpg" />
  <span property="name">Dell UltraSharp 30" LCD Monitor</span>
</div>

If the markup above looks similar to you, that was no accident. RDFa Lite 1.1 is designed to function as a drop-in replacement for Microdata.

The Bits that Don’t Matter

Only two features of Microdata aren’t supported by RDFa Lite; itemref and itemscope. Regarding itemref, the RDFa Working Group discussed the addition of that property and, upon reviewing Microdata markup in the wild, saw almost no use of itemref in production code. The schema.org examples steer clear of using itemref as well, so it was fairly clear that itemref is, and will continue to be, an unused feature of Microdata. The itemscope property is redundant in RDFa Lite and is thus unnecessary.

5 Reasons

For those of you that still are not convinced, here are the top five reasons that you should pick RDFa Lite 1.1 over Microdata:

  1. RDFa is supported by all of the major search crawlers, including Google (and schema.org), Microsoft, Yahoo!, Yandex, and Facebook. Microdata is not supported by Facebook.
  2. RDFa Lite 1.1 is feature-equivalent to Microdata. Over 99% of Microdata markup can be expressed easily in RDFa Lite 1.1. Converting from Microdata to RDFa Lite is as simple as a search and replace of the Microdata attributes with RDFa Lite attributes. Conversely, Microdata does not support a number of the more advanced RDFa features, like being able to tell the difference between feet and meters.
  3. You can mix vocabularies with RDFa Lite 1.1, supporting both schema.org and Facebook’s Open Graph Protocol (OGP) using a single markup language. You don’t have to learn Microdata for schema.org and RDFa for Facebook – just use RDFa for both.
  4. RDFa Lite 1.1 is fully upward-compatible with RDFa 1.1, allowing you to seamlessly migrate to a more feature-rich language as your Linked Data needs grow. Microdata does not support any of the more advanced features provided by RDFa 1.1.
  5. RDFa deployment is greater than Microdata. RDFa deployment continues to grow at a rapid pace.

Hopefully the reasons above are enough to convince most Web developers that RDFa Lite is the best bet for expressing Linked Data in web pages, boosting your Search Engine Page rank, and ensuring that you’re future-proofing your website as your data markup needs grow over the next several years. If it’s not, please leave a comment below explaining why you’re still not convinced.

If you’d like to learn more about RDFa, try the rdfa.info website. If you’d like to see more RDFa Lite examples and play around with the live RDFa editor, check out RDFa Play.

Thanks to Tattoo Tabatha for the artwork in this blog piece.

Full disclosure: I'm the current chair of the standards group at the World Wide Web Consortium that created the newest version of RDFa. RDFa 1.1 became an official Web specification last">http://www.w3.org/QA/2012/06/the_long_journey_to_rdfa_11.html">last month. Google started supporting RDFa in Google Rich Snippets some time ago and has recently">http://blog.schema.org/2012/06/semtech-rdfa-microdata-and-more.html">recently announced that they will support RDFa Lite for schema.org as well. These announcements have led to a weekly increase in the number of times the following question is asked by Web developers on Twitter and Google+: "What should I implement on my website? Microdata or RDFa?" This blog post attempts to answer the question once and for all. It dispels some of the myths around the Microdata vs. RDFa debate and outlines how the two languages evolved to solve the same problem in almost exactly the same way.

 

Here's the short answer for those of you that don't have the time to read this entire blog post: Use RDFa Lite - it does everything important that Microdata does, it's an official standard, and has the strongest deployment of the two.

Functionally Equivalent

Microdata was initially designed as a simple subset of RDFa and Microformats, primarily focusing on the core features of RDFa. Unfortunately, when this was done, the choice was made to break compatibility with RDFa and effectively fork the specification. Conversely, RDFa Lite highlights the subset of RDFa that Microdata did, but does it in a way that does not break backwards compatibility with RDFa. This was done on purpose, so that Web developers wouldn't have a hard decision in front of them. RDFa Lite contains all of the simplicity of Microdata coupled with the extensibility of and compatibility with RDFa. This is an important point that is often lost in the debate - there is no solid technical reason for choosing Microdata over RDFa Lite anymore. There may have been a year ago, but RDFa Lite made a few tweaks in such a way as to achieve feature-parity with Microdata today while being able to do much more than Microdata if you ever need the flexibility. If you don't want to code yourself into a corner - use RDFa Lite. To examine why RDFa Lite is a better choice, let's take a look at the markup attributes for Microdata and the functionally equivalent ones provided by RDFa Lite:
Microdata 1.0 RDFa Lite 1.1 Purpose
itemid resource Used to identify the exact thing that is being described using a URL, such as a specific person, event, or place.
itemprop property Used to identify a property of the thing being described, such as a name, date, or location.
itemscope not needed Used to signal that a new thing is being described.
itemtype typeof Used to identify the type of thing being described, such as a person, event, or place.
itemref not needed Used to copy-paste a piece of data and associate it with multiple things.
not supported vocab Used to specify a default vocabulary that contains terms that are used by markup.
not supported prefix Used to mix different vocabularies in the same document, like ones provided by Facebook, Google, and open source projects.
As you can see above, both languages have exactly the same number of attributes. There are nuanced differences on what each attribute allows one to do, but Web developers only need to remember one thing from this blog post: Over 99% of all Microdata markup in the wild can be expressed in RDFa Lite just as easily. This is a provable fact - replace all Microdata attributes with the equivalent RDFa Lite attributes, add vocab="">http://schema.org/" to the markup block, and you're done. At this point, you may be asking yourself why the two languages are so similar. There is almost 8 years of history here, but to summarize: RDFa was created around the 2004 time frame, Microdata came much later and used RDFa as a design template. Microdata chose a subset of the original RDFa design to support, but did so in an incompatible way. RDFa Lite then highlighted the subset of the functionality that Microdata did, but in a way that is backwards compatible with RDFa. RDFa Lite did this while keeping the flexibility of the original RDFa intact. That leaves us where we are today - with two languages, Microdata and RDFa Lite, that accomplish the same things using the same markup patterns. The reason both exist is a very long story involving politics, egos, and a fair amount of disfunctionality between various standards groups - all of which doesn't have any impact on the actual functionality of either language. The bottom line is that we now have two languages that do almost exactly the same thing. One of them, RDFa Lite 1.1, is currently an official standard. The other one, Microdata, probably won't become a standard until 2014.

Markup Similarity

The biggest deployment of Microdata on the Web is for implementing the schema.org vocabulary by Google. Recently, with the release of RDFa Lite 1.1, Google has announced">http://blog.schema.org/2012/06/semtech-rdfa-microdata-and-more.html">announced their intent to "officially" support RDFa as well. To see what this means for Web developers, let's take a look at some markup. Here is a side-by-side comparison of two markup examples - one in Microdata and another in RDFa Lite 1.1:
Microdata 1.0 RDFa Lite 1.1
<div itemscope itemtype="
">http://schema.org/Product">
  <img itemprop="image" src="dell-30in-lcd.jpg" />
  <span itemprop="name">Dell UltraSharp 30" LCD Monitor</span>
</div>
<div vocab="http://schema.org/" typeof="Product">
  <img property="image" src="dell-30in-lcd.jpg" />
  <span property="name">Dell UltraSharp 30" LCD Monitor</span>
</div>
If the markup above looks similar to you, that was no accident. RDFa Lite 1.1 is designed to function as a drop-in replacement for Microdata.

The Bits that Don't Matter

Only two features of Microdata aren't supported by RDFa Lite; itemref and itemscope. Regarding itemref, the RDFa Working Group discussed the addition of that property and, upon reviewing Microdata markup in the wild, saw almost no use of itemref in production code. The schema.org examples steer clear of using itemref as well, so it was fairly clear that itemref is, and will continue to be, an unused feature of Microdata. The itemscope property is redundant in RDFa Lite and is thus unnecessary.

5 Reasons

For those of you that still are not convinced, here are the top five reasons that you should pick RDFa Lite 1.1 over Microdata:
  1. RDFa is supported">http://blog.schema.org/2012/06/semtech-rdfa-microdata-and-more.html">supported by all of the major search crawlers, including Google (and schema.org), Microsoft, Yahoo!, Yandex, and Facebook. Microdata is not supported by Facebook.
  2. RDFa Lite 1.1 is feature-equivalent to Microdata. Over 99% of Microdata markup can be expressed easily in RDFa Lite 1.1. Converting from Microdata to RDFa Lite is as simple as a search and replace of the Microdata attributes with RDFa Lite attributes. Conversely, Microdata does not support a number of the more advanced RDFa features, like being able to tell the difference between feet and meters.
  3. You can mix">http://www.w3.org/TR/rdfa-primer/#using-multiple-vocabularies">mix vocabularies with RDFa Lite 1.1, supporting both schema.org and Facebook's Open Graph Protocol (OGP) using a single markup language. You don't have to learn Microdata for schema.org and RDFa for Facebook - just use RDFa for both.
  4. RDFa Lite 1.1 is fully">http://www.w3.org/TR/rdfa-lite/#the-attributes">fully upward-compatible with RDFa 1.1, allowing you to seamlessly migrate to a more feature-rich language as your Linked Data needs grow. Microdata does not support any of the more advanced features provided by RDFa 1.1.
  5. RDFa deployment">http://events.linkeddata.org/ldow2012/papers/ldow2012-inv-paper-1.pdf">deployment is greater than Microdata. RDFa deployment continues to grow at a rapid pace.
Hopefully the reasons above are enough to convince most Web developers that RDFa Lite is the best bet for expressing Linked Data in web pages, boosting your Search Engine Page rank, and ensuring that you're future-proofing your website as your data markup needs grow over the next several years. If it's not, please leave a comment below explaining why you're still not convinced. If you'd like to learn more about RDFa, try the rdfa.info">http://rdfa.info/">rdfa.info website. If you'd like to see more RDFa Lite examples and play around with the live RDFa editor, check out RDFa">http://rdfa.info/play/">RDFa Play. Thanks to Tattoo">http://tattootabatha.com/">Tattoo Tabatha for the artwork in this blog piece.
-- by @manusporny on July 3, 2012 at 9:50 pm