3. The method of claim 2 further comprising: building the inference chain for each answer included in the set of answers, wherein each inference chain links a characteristic selected from the one or more key characteristics, a reason selected from the one or more reasons, and a time period over which the respective answer changed.
2. The method of claim 1 further comprising: determining one or more key characteristics pertaining to each of the plurality of answers; identifying a set of answers that has changed over time, wherein the set of answers includes one or more answers from the plurality of answers; and identifying one or more reasons that the set of the answers changed by searching the domain specific corpus.