How can I include ratings in the site, with reference stored in the node table?
You can use Fivestar module for this.


  The Fivestar voting module adds a clean, attractive voting widget to nodes in Drupal 5, node and comments in Drupal 6, and any entity in Drupal 7.


You configure which content type should have the Fivestar module enabled; you can also set the permissions for the users who can vote etc. You will have multiple option to show the vote result on the configuration page of module.

I have used it in 3-4 e-commerce websites and it works simply great.