Let's make chatbots great again – Towards Data Science

These "good old-fashioned AI" systems were amazing in many ways, but they were also flawed. They required a lot of effort and engineering to get right. It was not a case of sticking a bunch of training data into a machine learning algorithm and turning the crank -- the natural language grammar that interprets user queries was carefully built by hand. Statistical techniques were not widely used, which meant that systems were inherently brittle. Queries had to have exactly the right form, or the chatbot would not understand.