I started building my expert system from generating decision tree like this: 
decision tree: <http://obrazki.elektroda.pl/6125718100_1336340563.png>

I used PC-Shell to build expert system, main code looks like:

```
result=e IF a>20, b=yes;
result=f IF a>20, b=no;
result=c IF a==20;
result=g IF a<20, d="is dry"; 

```

etc...

So where is artificial intelligence in this?
Doesn't it works like text based game where you answers and in the end you've got result?
And how in this example will work inference (forward and backward)?