Business rules execute on the server, so the usual server-side APIs are available to any scripts that might need to be run. Also available in business rules, is the current and previous objects, though previous isn't available when the business rule runs asynchronously.

Business rules have an added level of granularity as to when they can be run. An administrator can choose to have a business rule run either before, or after a record or update has been saved to the database.

Let's say for example, that I'm looking at an incident ticket, and I change the State field to Closed. That record update is then sent on its' way to the database, but if we have a business rule with the When field set to before, then any scripts or changes to that record will be executed prior to the record being saved to the database. This is important to note, because it gives you another means by which to reject an update before it hits the database using the setAbortAction() method of the current object...