Don't forget the FREE stuff!

Make a chat bot is hard. You need to design your topic and conversation carefully so you can cover most of your user's questions. You need to spend extra effort so you can handle stupid user spelling mistakes. You probably need to develop some adapter / interfacing code so you can look up a database or something. Even after you did all that, your bot will still look bad because one thing: human curiosity!

When people know they are talking with a chatbot, they tends to screw with it (probably because it would be improper to screw with a real person). They would try out things that will be way out of topic for your special bot. And if you don't handle it gracefully, they will think your bot "can't do anything!" even your bot handles relevant question perfect well.

Fortunately, their are existing chatbot that are made to do these kind of "free talk" with people. They are not build for information retrieving but more of a leisure chatting. The most famous bot is AliceBot, based on AIML. Even I think my CML is better and much easier to build a good information retrieving bot from scratch, I can't compete with AIML's AAA set when things come to "leisure talk".

AAA set contains 47205 conversation or "categories" in AIML's term. It took years to build and will make your bot looks smart when user went out of topic. The best part is, it's completely free. It would be stupid to not making use of this set (or a subset of it). Your chatbot can answer all your domain/topic related question. When things go out of scope, let them fall to the AAA set, so your bot can deal with unrelated question gracefully.

This is exactly what I did in making CML's Cindy Demo bot. It handles CML, shopping assistance Demo and weather questions. Everything else is handled by Plugin ActionProgramD, which is a open source plugin for a ProgramD version AliceBot, capable of running the unmodified AAA set. This way, a fairly smart chatbot is built in the matter of several hours.