ValueObjects are used entity attributes types to encourage code reuse and to simplify refactoring. A ValueObject starts with the valueobject keyword followed by a name like so:

valueobject Address {
    String streetName
    String streetNumber
    String zip
    String city
}

Value objects can be used as the type of an entity attribute as shown the next example.

entity Customer {
    String firstName
    String lastName
    Date birthDate
    String ssn
    Boolean premiumMember
    Address invoiceAddress
}