Column Family and Column Qualifier
Column qualifiers are the column names, also known as column keys. For example, in Figure 5-1, Column A and Column B are the column qualifiers. A table value is stored at the intersection of a column and a row. A row is identified by a row key. Row keys with the same user ID are adjacent to each other. The row keys form the primary index and the column qualifiers form the per row secondary index. Both the row keys and the column keys are sorted in ascending lexicographical order.