O'Reilly logo
  • Shuchi Mishra thinks this is interesting:

In UML, a relationship is represented by a line between two class rectangles, as shown in Figure 2-9. The line can be named to make it clear what the relationship is (e.g., “can be used for”), but it doesn’t need to have a name if the context is obvious. The pair of numbers at each end of the line indicates how many objects of one class can be associated with a particular object of the other class. The first number is the minimum number. This is usually 0 or 1 and is therefore sometimes known as the optionality (i.e., it indicates whether there must be a related object). The second number is the greatest number of ...