What is different bettween Cassandra NoSQL data model and SQL data model
Cassandra is a Columnar Store NoSQL Database, Which goes beyond the Key Value pairs.

A Column family in cassandra is a container for rows, like table in any RDBMS.

And These are Stored and represented in Json Formats.

Below are some links where you can get more info:

http://wiki.apache.org/cassandra/DataModel

http://www.datastax.com/docs/0.8/ddl/index

http://www.javageneration.com/?p=70