1. An information processing apparatus comprising: a calculation section configured to calculate similarity among a plurality of documents; an identification section configured to identify, in response to a change made to a first document, a second document having a similarity greater than or equal to a first criterion as compared to the first document before the change; a notification section configured to notify a user associated with the second document that the first document has been changed, in response to the change to the first document; and a necessity acquiring section configured to acquire necessity information indicating whether one or more other documents need to be changed due to the change to the first document, wherein the notification section further notifies the user associated with the second document of the necessity information.