A null bitmap is used in the variable-length record format to indicate that an attribute has no value. In a few odd cases, the majority of a tuple's properties are null. It is possible to minimise the...

A null bitmap is used in the variable-length record format to indicate that an attribute has no value. In a few odd cases, the majority of a tuple's properties are null. It is possible to minimise the cost of a null attribute to a single bit by modifying the way records are represented.