Usually, udevadm requires the sysfs device path of the device in question. But you can also ask udevadm which device path belongs to a certain device node. This gets really helpful if you combine these two queries.
Example: You want to get a list of attributes for a specific device. You do not know the complete device path; all you know is the device node /dev/sdb:
A nice document describing how to use this information to write udev rules can be found on http://www.reactivated.net/writing_udev_rules.html.