Cool objects Sleep on the Couch (Sebastian Bergmann)

Domain logic and persistence layer are tangled
    - No locality of change
    - No separation of concerns
    - Domain logic cannot be used - tested, for instance- without the persistence layer

How can we map the model to the database

Active record :
An object that wraps a row in a database table or view, encapsulates the database access and adds domain logic on top of it.
Active record may be used to implement Object-Relational Mapper (ORM) but it should never be used as one.

ORM:
Programming technique for converting data between incompatible type systems in relational databases and
object-oriented programming languages [that] creates a "virtual object database"

Unit of work:
Maintains a list of objects affected business transaction and coordinates the writing out of changes and the resolution
of concurrency problems.

Identity Map:
Ensures that each object gets loaded only once by keeping every loaded object in a map. Looks up objects using the map when
referring to them

Lazy Load:
An object that does not contain all of the data you need but knows how to get it.

Wakeup will be called by the Object Freezer