1. An information processing system comprising: a plurality of information processing apparatuses that perform a plurality of tasks defined by work flow information, wherein the work flow information is information that defines an order of the tasks and defines an information processing apparatus that assumes a host device for performing each of the tasks, one information processing apparatus selected from among the information processing apparatuses is definable as the host device, the information processing apparatus defined as the host device performs each of the tasks defined in the work flow information in the defined order, and one information processing apparatus selected according to a predetermined determination condition performs a task for which the work flow information defines the one information processing apparatus selected from among the information processing apparatuses as the host device.