I have a had time with the periods also.
I wanted to set up my iTunes library to help me learn more about a composer. So I turned to this website.
www.classicalarchives.com
You can go to this website for an explanation of the periods. I visit it frequently as I used it to classify composers. One composer could span two periods, what do you do? I decided to look up all composers in my library and classify them based on this website.
For example, all my composers in iTunes read like this....
Manuel de Falla (1876-1946); ESP
Manuel is listed as Modern Period
Arvo Pärt (1935-); EST
Arvo is listed as Contemporary Period
Erik Satie (1866-1925); FRA
Satie is Impressionist Period
I tried to used their periods to classify all my music.
Medieval
Renaissance
Baroque
Classical
Romantic
Late- / Post-Romantic
Impressionist
Modern
Contemporary
It is a bit of work but nice to have all the composers in iTunes match this format. And I learn something each time I browse through my library.
Of course I imported all my CD's into iTunes, but you could do the same with Microsoft Access. One place to know what do I have before I buy that CD for the second time.