The Model

ActiveRecord is an implementation of the Object-relational mapping pattern.
Idea: Turn database into a data structure so changes in data structure are reflected in database (persistent storage of data structure). Issues:
- When to update? When to select?
- How much of the SQL functionality do we implement?
- How much database-schema complexity do we allow?
Other implementations:
- NeXT's (now Apple's) WebObject
- Apache Cachenne
- Java Data Objects
Many people have implemented subsets of this idea for their own projects. Re-inventing the wheel.