When a business rule involves three or more graphical symbols, you can show the constraint as a note and attach the note to each of the symbols by a dashed line.

A solid diamond represents a stronger form of aggregation, known as composition.

In UML, a class is represented by a rectangle with three compartments separated by vertical lines.

A class is a concept, abstraction, or thing that makes sense in an application context.

A method defines the form or protocol of the operation, but not its implementation.