Value vs Entity objects (Domain Driven Design)

Question

I have just started reading DDD. I am unable to completely grasp the concept of Entity vs Value objects.. Can someone please explain the problems (maintainability, performan

Answer 1

I don't know if the following is correct, but I would say that in the case of an Address object, we want to use it as a Value Object instead of an Entity because changes to the entity would be reflected on all linked objects (a Person for instance).

Take this case: You are living in your house with some other people. If we would use Entity for Address, I would argue that there would be one unique Address that all Person objects link to. If one person moves out, you want to update his address. If you would update the properties of the Address Entity, all people would have a different address. In the case of a Value Object, we would not be able to edit the Address (since it is immutable) and we would be forced to provide a new Address for that Person.

Does this sound right? I must say that I was/am also still confused about this difference, after reading the DDD book.

Going one step further, how would this be modelled in the database? Would you have all properties of the Address object as columns in the Person table or would you create a separate Address table that would also have a unique identifier? In the latter case, the people living in the same house would each have a different instance of an Address object, but those objects would be the same except for their ID property.