You should take care, however, to make sure that your individual objects can stand alone as much as possible. Tightly coupled objects are objects that rely so heavily on each other that removing or changing one will mean that you have to completely change another one - a real bummer.

an object-oriented approach to data modelling – where data is described in terms of classes, attributes, and associations

Object hierarchies are very different from relational hierarchies. Relational hierarchies focus on data and its relationships, whereas objects manage not only data, but also their identity and the behavior centered around that data.

In object-oriented programming, information hiding (by way of nesting of types) reduces software development risk by shifting the code's dependency on an uncertain implementation (design decision) onto a well-defined interface. Clients of the interface perform operations purely through it so if the implementation changes, the clients do not have to change.

for example, comments and identifiers

If one object is part of another object, then we use a diamond at the start of the arrow (next to the containing object), and a normal arrow at the end.