Creating extents in ObjectStore
In Figure 27.15 we specified an extent for the SalesStaff class using the ODMG keyword
extent. On the second line of Figure 27.19 we have also specified an extent for
SalesStaff using the ObjectStore collection type os_Set. In the SalesStaff constructor, we have
used the insert method to insert the object into the class extent and in the destructor we have
used the remove method to delete the object from the class extent