Data Model
Cassandra is essentially a hybrid between a key-value and a row-oriented (or tabular) database.
- A column family resembles a table in an RDBMS. Column families contain rows and columns. Each row is uniquely identified by a row key. Each row has multiple columns, each of which has a name, value, and a timestamp. Unlike a table in an RDBMS, different rows in the same column family do not have to share the same set of columns, and a column may be added to one or multiple rows at any time.
Each key in Cassandra corresponds to a value which is an object. Each key has values as columns, and columns are grouped together into sets called column families. Also, each column family can be grouped in super column families.
Thus, each key identifies a row of a variable number of elements. These column families could be considered then as tables. A table in Cassandra is a distributed multi dimensional map indexed by a key.
Furthermore, applications can specify the sort order of columns within a Super Column or Simple Column family.
Read more about this topic: Apache Cassandra
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