The disadvantages of the index approach are that it requires more file space (the tables use more over-head than the pointers do) and that the DBMS programming task is more complex.
Note that the application programming task is not necessarily any more or less difficult—but it is more complex to write DBMS software that processes indexes than it is to write software that processes linked lists. Finally, modifications are usually processed more slowly because of the reading and writing actions required to access and maintain the values in the occurrence tables.