You always want to convey some message via your interface. Your messages can be known in advance. You may be able to create a system which ask qustions to recognize your input in the known format. ie.. Presenting your on input into different format that might be acceptable to you. Which is offcourse 2 step process but may help you.

The message conveyed can be put at definite place in the in the scheme of things than if would become more easier to ask questions.

Consider the case:

Travel Booking:: "I want to go from London to New York."

If it recognizes  'from London' and 'To New York' that would be it. Because it has definte templates to handle the information.