Learning the FSA Tool
Suppose that you wanted to determine whether a binary string has an even number of ones. This is called checking for even parity. This can be accomplished by the finite state automaton below. You should type in some input values and then run the fsa on these values. To do this, follow these steps:
1. Click on the input tape (if the input tape shows no tape squares, minimize the browser window and then maximize it again).
2. Type in a string of 1's and 0's
3. Click on the Run button. This moves the tape input pointer to the first square.
4. Click on the Step button until the string is either accepted or rejected. If you have headphones, you can hear some accompanying sound effects.
5. Click on the Step button one more time to complete processing. At this point you can erase the input tape using the backspace button and retype new input.
There are some bugs still in this applet, some having to do with Netscape. If you have trouble, you may need to click on the Reload button of Netscape to restart the applet.
After you have run this fsa a few times, you can use this applet to build your own fsa's. To do this,
1. Make sure the fsa has finished running
2. Click on the Clear button.
3. Click on the Alphabet button. Select the alphabet symbols you need for your fsa by clicking on them (clicking on a selected alphabet symbol also clears it). You can modify your alphabet selections at any time by clicking again on the alphabet button.
4. In the fsa pane, you can create a new state by positioning the cursor and performing a <ctrl>-left click.
5. You can move any states you create by left clicking and dragging.
6. You designate a start state by right clicking on the state. The same holds for designating accept states.
7. You can delete a state by right clicking on it as well.
8. You create arrows between states with <ctrl>-left click in a state, and then dragging the arrow to the state you want to connect to.
9. You assign symbols to arrows by right clicking on the arrow head and then selecting Edit Symbols. Choose all of the symbols you want to assign to that arrow by left clicking each symbol.
10. You can add state labels and state descriptions also by right clicking on a state.
11. You can run your fsa in the usual fashion.
If for some reason, the applet hangs, you will need to start over by reloading the browser page. You also cannot save your work to a file due to disgusting Java/browser security issues that have not yet been resolved by Sun after these many years. So, you will need to print your work when you are done.
Give it a try.
