Operator classes
An operator class tells the database server which data type (or types) it can index using a secondary-access method. The operator class must follow the requirements of the access method. The secondary-access method builds and accesses an index. An operator class associates a group of operators with a secondary-access method. When you extend an operator class, you provide additional functions that can be used as filters in queries and for which the database server can use an index.
The database server provides a default operator class for the built-in secondary-access method, a generic B-tree. This default operator class uses the relational operators (<, >, =, and so on) to order values in the generic B-tree. These relational operators are defined for the built-in data types.