SMIRKS...
...is a reaction transform language.
...is a superset of reaction SMILES.
...is a subset of reaction SMARTS.
...has behaviors that don't exist in the other languages.
...can describe reaction mechanisms with varying degrees of specificity and generality.
 

     The extensions described here are fully implemented and supported throughout the Daylight system. The SMILES and SMARTS languages are redefined with a larger scope to include reaction features. It is reasonable to refer to a "Molecule SMILES" or a "Reaction SMILES", but from this version on, the SMILES and SMARTS languages are defined to include support for reactions.

Further Information and full course material please go to the DAYLIGHT.COM

courtesy:http://www.daylight.com