Explained ORM in Ruby on Rails?

ORM_in_ror.txt

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* ORM is Object Relational Mapper. It means you don't have to manually call the database yourself; the ORM handles it for you.
* Ruby on Rails uses one called ActiveRecord, and it's a really good one.
* ORM allows you to do things such as:
      User.find(50).contacts
      Instead of manually writing a SELECT statement with JOINs, WHEREs, etc.
      
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* Active Record as an ORM Framework
* Active Record gives us several mechanisms, the most important being the ability to:

> Represent models and their data.
> Represent associations between these models.
> Represent inheritance hierarchies through related models.
> Validate models before they get persisted to the database.
> Perform database operations in an object-oriented fashion.

MORE DETAILS: 
 http://api.rubyonrails.org/files/activerecord/README_rdoc.html
 http://www.sitepoint.com/orm-ruby-introduction/
 http://guides.rubyonrails.org/active_record_basics.html