Sometimes change hurts. You know what I’m talking about if you need to change the multiplicity of a relationship (let’s assume you talk about an ordinary sql database). For instance: From 1 to 1 To1 to many For instance, say it’s an adress. The assumptions made when there is only one adress permeates throughout the applications. For instance a person must have bills sent to a different adress (his/her accountant or something similar). However, when contacted, any mail needs to be sent to the home address.[...]