Indexes

    type_spec : 'index' '<' simple_type_spec ',' simple_type_spec '>'

Attributes can be indexes; these are called ``manual indexes'', meaning that they are explicitly intialized, loaded, and manipulated by an application program.

    typedef     long ssn;     // social security number
    interface Person {
    public:
        attribute   string name;
        attribute   ssn    social_security_number;
    };

    interface IndexObject {
    public: 
        attribute index<string,Person> name_to_person; 
        attribute index<ssn,string>    ssn_to_name; 
    };

The index declaration index<string,Person> is equivalent to index<string,ref<Person> >; the two declaration styles can be used interchangeably.