In one embodiment, a database server registers one or more functions included in a user-defined index that includes one or more auxiliary properties. The one or more functions are operable to generate index entries of the user-defined index for the one or more auxiliary properties. The one or more auxiliary properties are different than, and in addition to, a primary property of the user-defined index that provides for evaluating a query operator. The database server receives a first statement that defines the user-defined index, where the first statement includes one or more parameters that define the one or more auxiliary properties. The database server invokes the one or more functions in response to the first statement, where the one or more functions when invoked generate and store the index entries of the user-defined index according to the one or more parameters that define the one or more auxiliary properties.