Abstract Data Types

Except for FN_attrvalue_t and FN_identifier_t, the types defined in the interface hide their actual data representation from the client. The client performs every operation on an object of one of these types through a well-defined interface for that data type.

When the client accesses these objects, the client refers to the objects solely through a handle to an object. Operations are provided to create objects of each type and to destroy them. The creation operation returns a handle to the new object. The destroy operation releases all resources associated with the object.

The only information about this handle revealed to the client is that it is a pointer type. The client cannot assume what this handle points to. In particular, the handle might not point directly to the memory containing the object's actual state.

The value 0 is defined for all pointer types. The functions that return handles in the interface return the value 0 as an indication of failure. The values 0 and NULL are equivalent.