rdf

We've seen in the previous four articles that RDF has the potential to be a game-changer when it comes to linked data on the web. The fact that is it an open standard, easy to understand, and implementable on sites from those powered by the most complex web applications to simple hand-built web pages makes it easy to understand why so many people are starting to look at RDF as one of the future cornerstones of the web. Luckily for the Drupal community, our fearless leader Dries Buytaert recognized this in 2008 and suggested that Drupal take the lead in implementing RDF among open source content management systems. Since then, a number of individuals have stepped up and committed to working to get RDF functionality in Drupal 7. The Semantic Web group on Drupal.org is the focal point of the work that is going on in this effort. Earlier this year, they posted a video about what will be possible when RDF functionality is available. They showcased advanced search results and the ability to navigate the relationships that RDF triples provide with HTML documents.

In the first three parts of this series, we've looked at what RDF will do for you as both a consumer and a provider of RDF data and we've had a quick primer on what exactly implementing RDF entails. Turning our attention back to Drupal, this article will take a look at the state of RDF in Drupal 6 and some of the available contribued modules. Tomorrow's article will take a look at what the next version of Drupal will offer in terms of RDF. Drupal 6 does not have any RDF functionality in core. If you want to implement anything having to do with RDF in Drupal 6, you'll need to utilize contributed modules. Only a few of the RDF-related contribued modules for Drupal have even had official releases - the majority of them are still somewhere in the development process. While reviewing the existing RDF modules for Drupal 6, I found that I could categorize them into two categories - "Provider Modules" and "Consumer Modules". Those in the former category are designed primarily to help you RDF-ize your site's content. Modules in the "Consumer" category are generally designed to help you consume, use, and display RDF data from various sources. In some cases, there is some overlap, so this categorization is more for convenience than anything else.

If you've read the first couple of installments of this series, you should have a pretty good idea of what the "semantic web" is by now. By providing precise meaning to a site's content, applications can take advantage of these machine-readable hints to link data together across sites in a myraid of ways. Before you jump in the deep end of the semantic web pool, there's a few more things you should have a clear understanding of. As I previously defined, RDF stands for Resource Description Framework . This is a family of standards for describing content on the web. The vast majority of current and future Drupal implementations of RDF are actually RDFa ( Resource Description Framework in Attributes ), a set of extensions to XHTML. RDF is normally implemented using XML; while this is possible with Drupal, RDFa allows Drupal to implement RDF as part of the standard content displays.

Even if you're not ready to implement RDF into your Drupal site, there's still a number of reasons why you should be excited about the Semantic Web. The fact that data will be linked from web site to web site (regardless of the underlying technology running the site) will lead to powerful Semantic Web applications - most of which haven't even been imagined yet. First and foremost, search will be revolutionized. Imagine being able to search for a specific person - not just the person's name. This is a subtle but important distinction. Currently, when you type "Dave Matthews" into your favorite search engine, the results you see are based on the words "Dave" and "Matthews". You'll see results about Dave Matthews, about people with the name "Dave" and/or "Matthews", about the orgin of the words "Dave" and "Matthews", etc... The search engine doesn't know that you're looking for a specific person with the name "Dave Matthews". With the Semantic Web, you'll be able to specify, "find me the person with the name 'Dave Matthews'". You'll even be able to perform "deeper" searches by specifying things like "find me all events having to do with Drupal taking place between now and July". Other than search, the Semantic Web will also provide you with the ability to do stuff with this data. For example, let's say you perform the Drupal events search from the previous paragraph and you're looking at the results. Because the data returned will have meta-data attached to it, future software tools will allow you to click on a returned event, and see if you're available on that date and time. If so, another click will seamlessly add it to your calendar. If you're familiar with Mac OS X , it's like data detectors on steriods. Really good steriods.

RDF. Semantic Web. Giant Global Graph. Food for Robots. By now you've probably heard all of these phrases, but relatively few of us have actually done anything with them. For example, I try to follow all the RDF modules on Drupal.org , read all the blog posts regarding Drupal and RDF but I've yet to implement anything having to do with RDF on any of the sites I develop or maintain. Why is this? Am I behind the curve? The answer is two-fold. First, I have yet to have any clients specifically ask for RDF functionality in their web sites. Secondly, I hadn't been convinced that recommending that my clients spend the time and money to implement an RDF solution is a sensible move for them. The reason I decided to research and write this series of articles is to figure out if and why I should recommend implementing RDF functionality to my clients. Prior to performing the research for this series, my knowledge of RDF was limited to water-cooler-conversation type knowledge. Big on bulletpoints, small on details. I was aware that RDF will, in the future, be used by search engines to provide better search results. I was also aware that by "tagging" web site content with RDF would enable a "richer" experience. The one example I would relay to people was a vCard -powered business card embedded on a web page using microformats that allowed the user's computer to do something with the contact information. Amusingly, it turned out that my one RDF example didn't even involve RDF, and that the vCard format was actually called hCard when used as a microformat. I had a lot to learn.