2.1 vocab, typeof, and property

RDFa, like Microformats [microformats] and Microdata [microdata], enables us to talk about things on the Web such that a machine can understand what we are saying. Typically when we talk about a thing, we use a particular vocabulary to talk about it. So, if you wanted to talk about People, the vocabulary that you would use would specify terms like name and telephone number. When we want to mark up things on the Web, we need to do something very similar, which is specify which vocabulary that we are going to be using. Here is a simple example that specifies a vocabulary that we intend to use to markup things in the paragraph:

<p vocab="http://schema.org/">
   My name is Manu Sporny and you can give me a ring via 1-800-555-0199.
</p>

In this example we have specified that we are going to be using the vocabulary that can be found at http://schema.org/. This is a vocabulary that has been released by major search engine companies to talk about common things on the Web that Search Engines care about – things like People, Places, Reviews, Recipes, and Events. Once we have specified the vocabulary, we need to specify the type of the thing that we're talking about. In this particular case we are talking about a Person, which can be marked up like so:

<p vocab="http://schema.org/" typeof="Person">
   My name is Manu Sporny and you can give me a ring via 1-800-555-0199.
</p>

Now all we need to do is specify which properties of that person we want to point out to the search engine. In the following example, we mark up the person's name, phone number and web page. Both text and URLs can be marked up with RDFa Lite. In the following example, pay particular attention to the types of data that are being pointed out to the search engine, which are highlighted in blue:

<p vocab="http://schema.org/" typeof="Person">
   My name is
   <span property="name">Manu Sporny</span>
   and you can give me a ring via
   <span property="telephone">1-800-555-0199</span>
   or visit 
   <a property="url" href="http://manu.sporny.org/">my homepage</a>.
</p>

Now, when somebody types in “phone number for Manu Sporny” into a search engine, the search engine can more reliably answer the question directly, or point the person searching to a more relevant Web page.

2.2 resource

If you want Web authors to be able to talk about each thing on your page, you need to create an identifier for each of these things. Just like we create identifiers for parts of a page using the id attribute in HTML, you can create identifiers for things described on a page using the resource attribute:

<p vocab="http://schema.org/" resource="#manu" typeof="Person">
   My name is
   <span property="name">Manu Sporny</span>
   and you can give me a ring via
   <span property="telephone">1-800-555-0199</span>.
   <img property="image" src="http://manu.sporny.org/images/manu.png" />
</p>

If we assume that the markup above can be found at http://example.org/people, then the identifier for the thing is the address, plus the value in the resource attribute. Therefore, the identifier for the thing on the page would be: http://example.org/people#manu. This identifier is also useful if you want to talk about that same thing on another Web page. By identifying all things on the Web using a unique Uniform Resource Locator (URL), we can start building a Web of things. Companies building software for the Web can use this Web of things to answer complex questions like: "What is Manu Sporny's phone number and what does he look like?".

2.3 prefix

In some cases, a vocabulary may not have all of the terms an author needs when describing their thing. The last feature in RDFa 1.1 Lite that some authors might need is the ability to specify more than one vocabulary. For example, if we are describing a Person and we need to specify that they have a favorite animal, we could do something like the following:

<p vocab="http://schema.org/" prefix="ov: http://open.vocab.org/terms/" resource="#manu" typeof="Person">
   My name is
   <span property="name">Manu Sporny</span>
   and you can give me a ring via
   <span property="telephone">1-800-555-0199</span>.
   <img property="image" src="http://manu.sporny.org/images/manu.png" />
   My favorite animal is the <span property="ov:preferredAnimal">Liger</span>.
</p>

The example assigns a short-hand prefix to the Open Vocabulary (ov) and uses that prefix to specify the preferredAnimal vocabulary term. Since schema.org doesn't have a clear way of expressing a favorite animal, the author instead depends on this alternate vocabulary to get the job done.

RDFa 1.1 Lite also pre-defines a number of useful and popular prefixes, such as dc, foaf, and schema. This ensures that even if authors forget to declare the popular prefixes, that their structured data will continue to work. A full list of pre-declared prefixes can be found in the initial context document for RDFa 1.1.