Main differences in plugins between vB3 and vB4

[NLP-er]

Hello.

What are the main differences between vB3 and vB4 in plugins architecture? If someone could describe it in advanced level.

Especially answering on those questions:
- Does old hooks names changed?
- How changed plugin.xml schema?
- Does there were big changes in DB structure?
- Does old functions where moved to other files?

And in shorter way - what are most common things which should be changed if you have already existing plugin for vB3 and want to make it ok for vB4?

Great thanks for all hints