If you are building a Travel Booking bot, there will be several user inputs that have to be validated before an Air Traffic Service/API can be called. With Watson Assistant ( formerly Watson Conversation Service) you can do that effortlessly in the tooling using Spring Expression Language (SpEL) methods and expressions without having to take it to application side. You can process values extracted from user inputs by writing methods and expressions that access objects and properties of objects.
To understand the technology via examples, read my blog here. The blog will assist in understanding how to validate user inputs in Travel Booking bot scenario using Spring Expression Language methods and expressions in Watson Assistant.