Slide 19 of 52
Notes:
Notice that:
- The Driver and BusRoute instances have no explicit ID field; all references are based on their unique object-identity, which is managed by the system not the user's application.
- Each attribute of the Driver and BusRoute instances is a pointer to another object.
- An instance attribute can point directly to a set of other objects (this set would be an instance of a predefined Set class).
- Each BusRoute instance has a pointer to its Driver, and each Driver instance has a pointer to its set of BusRoutes; this supports direct navigation between them for queries without the need for a separate join table.
- Each Driver instance knows how to manage its associations with BusRoutes, presumably with the help of a graphical interface. BusRoute instances could be made capable of managing their link to the Driver; it would also be a simple matter for either of them to synchronize the other's attribute.
- This is going deep into the internal design. Some OO systems present a special user interface for managing relationships so that the user never needs to see 'pointers' at all.
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