e3value user guide
A value object is a money- or non-money object that
Value objects should be countable or measurable, which means that it is meaningful to ask how many of them there are resp. how much if it there is. Discrete objects like cars, vacuum cleaners and furniture are countable. Continuous objects like energy, money or coaching need a measurement unit to be able to tell how much of it there is. An amount of energy can be measured in kWh, amounts of money can be measured in some currency (florins in this book, represented by the symbol f), an amount of coaching could be measured by the the number of contact hours.
The measurement unit used for a value object must be agreed by all stakeholders in the model that deal with the value object.
Value objects have economic value, defined differently for money- and non-money objects. A money object has a definite currency value that is known and agreed on by actors. If actor A pays f10 to actor B, then B receives f10 from A.1 Money objects are also called value-in-transfer [6].
A non-money object may be
Some of these can be discrete (a car, a taxi trip, attending a concert), others are continuous (energy, coaching, playing).
The value of a non-money object for an actor depends on the increase in utility when the actor consumes or uses the value object. Different people may assign different value to non-money objects, and one person may even assign a different value at different times. For example, the value of a cold beer to me on a hot summer day is different from its value on a cold rainy day. The value of an non-money object is often called value-in-use [6].
A value object is represented by showing the name of the object next to a value transfer enclosed in square brackets (as [value object]). In figure 3.1, two value objects are represented: Money and Train trip. The name of a value object should express the economic utility of the object. It should explain why an object is of value to an actor.