reading Adruino data from my mac


How do I create an application using xcode that will read information from arduino?
For example, I want my Mac (master) to instruct Arduino board (slave) to read the temperature from a sensor, and present it on the Mac screen.
I'm looking for code samples (for xcode as well as for the Adruino borad) that implement such a communication channel.
Can it be USB based?
Thanks a lot guys!

The USB interface of the Arduino reads and writes like a serial port. If you can find examples of using serial ports in XCode then you should be all set.