1. A dialog assistant embodied in one or more machine readable storage media, the dialog assistant accessible by a computing system to conduct a clarification dialog with a user by: identifying a clarification target, the clarification target comprising a machine-readable version of a portion of a human-generated conversational natural language input needing clarification, the clarification target being less than the whole input; determining a clarification type relating to the clarification target, the clarification type indicating a type of clarification needed to clarify the intended meaning of the clarification target; presenting a conversational natural language clarification question based on the clarification type, the clarification question referring to the clarification target; and processing a human-generated conversational natural language response to the clarification question to clarify the intended meaning of the clarification target.