Can variables be automatically updated throughout a book

We use variables for our document's part and revision numbers. I know you can update variables within a file but we would like to be able to update the variable throughout all of the files in the book. Is there a way that we can do this? It would save maintenance time because many of our books have a lot of chapters.

We are using Frame 8 on Windows XP Profession, version 5.1.

Thanks,

Tim