- Smart Types” for model attributes (A smart type is a primitive type that knows that it has been set and changed),
- Explicit attached “business rule objects”
- Rules can navigate the model using xslt
Use of the composite pattern for the model makes for a very robust model component (rules can survive the addition of nodes above them in the tree). This is very easy to self check, maps directly to requirements, has a single obvious implementation point for almost any functionality to be added.
One of the key points is that the model is responsible for holding data, validating data and performing other buisiness functions. The model is not responsible for data persistance.
The components of the system are:
Data Access Layer (D)
Typically the controllers constructor has a signature of C(M,V,D).
This allows us to keep the Model independent of the database and the View.
Most business rules belong in the model – the exceptions being referential integrity and uniqueness constraints that have to be on the database.