Domain Model (2)

DDD - Modelling the Domain - Value Objects

There are elements of the Domain Model without any conceptual identity which are typically used to characterise Entities (Evans, 2003). Those elements are called Value Objects and their significance is often neglected (Vernon, 2013). Examples of Value Objects are: Zip Code, Order Number, Phone Number, Money, Currency, Date, Date Range, E-mail Address, URL etc. Value Objects express domain concepts and are part of the Ubiquitous Language (Evans 2003; Vernon, 2013).

DDD - Modelling the Domain - Entities

Entities are objects of the domain model with a distinct identity and a life cycle (Evans, 2003). Moreover, the key defining characteristic is not the values of their properties which could change over time (Evans, 2003). The uniqueness of an Entity's identity is defined by the model and does not change during its lifetime (Evans, 2003).