So far, our approach to working with databases has been to start with a domain model, and then use NHibernate to generate appropriate database schema matching that domain model. Database schema generated this way is fit for purpose, and leads to a frictionless NHibernate experience. Even if you do not use NHibernate to generate database schema, you could build one that is closest to your domain model. This approach works great for green field applications and is most recommended approach. But if you are working with a legacy database, then what was simple so far may start showing its complex side. It is also worth noting that a legacy database, in the context of this chapter, is not just a database that is old, it is more of a situation that leads to the domain model differing from the database schema.

You could also be working with a database which is not legacy at all, but the application you are working on is not the only (or the primary) application...