1. A medical device system comprising: a first medical device; a first memory provided corresponding to the first medical device; a second medical device; and a second memory provided corresponding to the second medical device, wherein the first memory includes a first shared memory area provided corresponding to the first medical device and a second shared memory area provided corresponding to the second medical device, the second memory includes a third shared memory area provided corresponding to the first medical device and a fourth shared memory area provided corresponding to the second medical device, the first medical device includes a first writing unit that dynamically writes, into a certain memory area included in the first shared memory area, definition data that defines a method for using the certain memory area and data corresponding to the definition data, and the second medical device includes a second writing unit that dynamically writes, into a certain memory area included in the fourth shared memory area, definition data that defines a method for using the certain memory area and data corresponding to the definition data.