The last type provides means by which one can build a superdatabase. This superdatabase is able to access other databases. Making this database searchable makes also all other databases searchable if they provided a index list. This system makes is possible for database to specialize on specific parts of information. Two examples are given below.
Booksellers have specific information on prices, whereas newspapers and magazines have book reviews.
The unique ID would be the ISBN number. One database might consist of physical properties while others may contain spectra. And this is the case. It is certainly possible to make a superdatabase without a DAD file like system. CambridgeSoft Corp. However, every database have to be indexed by the superdatabase.