"#"符号在UML类图中的含义是什么？

class Person {
  +name: String
  +age: Integer
  +address: Address #
}

class Address {
  +street: String
  +city: String
  +state: String
  +zip: String
}

class Customer {
  +name: String
  +address: Address #
}

class Supplier {
  +name: String
  +address: Address #
}

class Address {
  +street: String
  +city: String
  +state: String
  +zip: String
}