In my country, the Expert System class is mandatory, if you want to take the AI specialization in most universities. In class, I learned how to make a rule-based system, [forward chaining][2], [backward chaining][3], [Prolog][1], etc. 

However, I have read somewhere on the web that [expert systems][4] are no longer used.

Is that true? If yes, why? If not, where are they being used? With the rise of machine learning, they may not be as used as before, but is there any industry or company that still uses them today?

Please, provide some references to support your claims.

  [1]: https://en.wikipedia.org/wiki/Prolog
  [2]: https://en.wikipedia.org/wiki/Forward_chaining
  [3]: https://en.wikipedia.org/wiki/Backward_chaining
  [4]: https://en.wikipedia.org/wiki/Expert_system