When DDD should be considered ?

This is a recurring question on the DDD yahoo group. And there was a simple explanation during the ParisJug talk.

DDD is not a silver bullet for all application development, it just helps to manage complexity when the complexity comes from the domain.

No need for DDD when working on a technical application or a small application with few interactions.

You could benefit from DDD when your application looks like the Cargo sample :

• Route containers based on transports availability
• Take cost and time into account
• Know where are the boats
• Organize loads and unloads
• Manage container storage (emit order of missions for employees on site)
• Provide container tracking and tracing to clients
• Transports can be late, manage it
• Transports can be canceled, manage it
• Contracts can be changed, destination can change
• Containers can be incorrectly routed even if emitted orders where correct, manage it.
• Manage taxes
• Manage time zones
• Manage currencies
• Manager constraints and local rules on dangerous containers contents

In this kind of application, the complexity doesn’t come from an Xml web service or a database schema. Even without taking account any technical concern, it is complex !

So there is a simple rule of thumb to know if DDD could apply (independently from the size of the project) :

Try DDD if Domain Complexity >> Technical Complexity

In other case you can just go with your preferred classic architecture.