.image = value;
we use OpenAccess ORM http://www.telerik.com/products/orm.aspx for the data layer in Sitefinity. All the fields are created by OpenAccess, however, some fields are defined during the compilation (Open Access uses technique called enhancing to add some code to the persistent classes during the compilation), while others are added dynamically (during the runtime).
Every time you define a member inside of a class (prior to compilation), those are going to be created by OpenAccess on the first connection to the database and we generally call them static. On the other hand, if you use our DynamicData fluent API, you are adding fields after the compilation and hence we call them dynamic types / fields.
Content base class uses horizontal inheritance, meaning that each subclass will have a separate database table in which ALL (as opposed to vertical) data will be stored.
I hope this sheds some light on the inner workings of Sitefinity.