This is the actual piano on which the composer created some of his greatest works.求这句的语法结构.另外为什么用on?

分析：
该句是一个主、系、表结构,其中表语又带了定语从句.
This is the actual piano 【on which the composer created some of his greatest works.这是一个定语从句】
这个复合句可以还原成两个简单句,分别是：
1.The composer created some of his greatest works on a piano.作曲家在一架钢琴上创作出了他的一些优秀作品.
2.This is the actual piano.这就是那架钢琴.
再把这两个简单句合二为一：
This is the actual piano on which the composer created some of his greatest works.
介词on 就是这么来的.
几乎所有的定语从句都可以用这个办法进行“还原- 再合成”来进行验证.
希望以上解释能够有助于这位网友解开疑问.