CQL 3 introduces these collection types:
In a relational database, to allow users to have multiple email addresses, you create an email_addresses table having a many-to-one (joined) relationship to a users table. CQL 3 handles the classic multiple email addresses use case, and other use cases, by defining columns as collections. Using the set collection type to solve the multiple email addresses problem is convenient and intuitive.
Another use of a collection type can be demonstrated using the music service example.