Aggregation is a more specialised form of association. Aggregation tells you that the relationship is a whole/part association.
Yes. Which actually means that there is no cycle in the object graph allowed - the whole must not be part of itself.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus