The two main part of wit.ai are:
intent classification
entity extraction
For entity extraction, it uses a duckling library that they recently open-sourced it, and you can find a detailed description of the algorithm there.
Wit.ai is not a set of prebuild intents you have to register to. With Wit.ai you can create the intents you need for your app.
Creating an intent is very easy: you just have to provide a few examples of how end-users will express this intent.
For more information regarding this, refer the following link:
https://wit.ai/docs/complete-guide
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