1. Microdata
2. Microformat
3. RDFa
They represent different trade-offs in terms of ease of authoring versus expressibility.
<span style="font-size:130%;">Interesting facts about microdata:
Microdata is HTML5 microdata specification. It is a way to label the content data to describe specific type of information. This doesn't supported by Yahoo
Ex: Person, Event, ....
Microdata uses the simple html tags div or span
Ex1: <div itemscope="" itemtype="http://data-vocabulary.org/Person">
My name is <span itemprop="name">Bob Smith,
but people call me Smithy.
Here is my homepage:
www.example.com.
I live in
<span itemprop="address" itemscope="" itemtype="http://data-vocabulary.org/Address">
<span itemprop="locality">Albuquerque,
<span itemprop="region">NM
and work as an <span itemprop="title">engineer
at <span itemprop="affiliation">ACME Corp.
Ex2:
Rating: 8.5
Microformats are the easiest to write and understand, but may not fill all your metadata needs. In particular, you may not find an appropriate vocabulary to represent your information.
Interesting facts about RDFa:
eRDF and RDFa allow you to work with any RDF or OWL vocabulary, and create your own vocabulary or reuse existing ones. eRDF is a subset of the full RDF model; for example, you can only make statements about the current page. RDFa offers all the features of RDF, making it the most complex of the three formalisms but also the most powerful one.
Source:
http://www.google.com/support/webmasters/bin/answer.py?answer=176035
