Good essay on the Domain Model (from 2006)

Essay: The Database Model is the Domain Model
By Frans Bouma

Preface

To work with data on a semantic basis, it's often useful to specify general definitions of the elements a given portion of logic will work with. For example, an order system works with, among other elements, Order elements. To be able to define how this logic works, a definition of the concept Order is practical: We will be able to describe the functionality of the system by specifying actions on Order elements and supply with that a definition of that element Order.

This Order element contains other elements (values like the OrderID and ShippingDate) and has a tight connection with another element, OrderRow, which in turn also contains other elements. You can even say that Order contains a set of OrderRow elements like it contains value elements. Is there a difference between the containment of the value OrderID and the containment of the set of OrderRow elements? The answer to this question is important for the way the concept of Order is implemented further when the order system is realized with program code.