Question

Is is correct to assume that migrations in ruby on rails are simply updates to any database. And that the rake db:migrate script only serves to actualize these changes?

Answer 1

Yes.

Migrations are a convenient way for you to alter your database in a
structured and organized manner. You could edit fragments of SQL by
hand but you would then be responsible for telling other developers
that they need to go and run them. You’d also have to keep track of
which changes need to be run against the production machines next time
you deploy.

Active Record tracks which migrations have already been run so all you
have to do is update your source and run rake db:migrate. Active
Record will work out which migrations should be run. It will also
update your db/schema.rb file to match the structure of your database.

Migrations also allow you to describe these transformations using
Ruby. The great thing about this is that (like most of Active Record’s
functionality) it is database independent: you don’t need to worry
about the precise syntax of CREATE TABLE any more than you worry about
variations on SELECT * (you can drop down to raw SQL for database
specific features). For example you could use SQLite3 in development,
but MySQL in production.

Source: Ruby on Rails Guides: Migrations