Collapse child entity sets into the father entity set

To apply this method one operates as follows:

1. one removes the “ISA” construct,
2. one moves the attributes of each child entity set to the father entity set,
3. one deletes the child entity sets,
4. one adds a “type” attribute to the father entity to allow space for storing a value that discriminate every former child entity, since child entity sets, that served this purpose, are no longer available,
5. one attaches any child orphaned relationship sets to the father entity set.

This method may always be applied, although care must be taken, as many NULL values may be introduced by the new structure.

Exercise:

1. Restructure the diagram as described above.
2. Click at compare with solution to verify your result.

Notice how less precisely the new structure represents the enterprise at hand. Administrative tasks can now be assigned to technical staff, as well.

M3.02 E-R Restructuring