Over the previous 12 chapters, we've thoroughly explored Cassandra's capabilities from the perspective of application developers. All of our interaction with Cassandra has been through CQL, and we've explored a robust set of features available to us via the CQL interface. We've found that one of the big appeals of Cassandra is the rich set of data structures available to us for domain modeling; structures such as compound primary keys, collection columns, and secondary indexes are part of  what sets Cassandra apart from other distributed databases.
As it turns out, CQL is an abstraction on top of a much less sophisticated data structure that underlies all the data stored in Cassandra. Commonly referred to as the Thrift interface, named after the protocol used to interact with Cassandra at this level, this layer represents all data using an ad hoc key-value structure...
