What exactly is Domain Driven Design (DDD)?

We have been using many of the principles and patterns of DDD over the past many years. During domain modeling we have often used the concepts of boundary contexts, entity objects, value objects, aggregates and repository pattern, etc.

But based on my humble experience, I think DDD is much more than the usage of these patterns. DDD is a "thought-process" - the way you think about the problem domain, the way you interact with the domain experts & business stakeholders and the way you articulate the technology realization of the business need. This in a nutshell is the greatest boon of following DDD. The business and IT speak the same 'ubiquitous' language and this in turn bridges the "Business-IT gap" :)

That's the reason, the famous DDD book by Eric Evas states that DDD tackles Complexity in the Heart of Software. Mapping your software model as close to the real-life domain as possible helps us in managing the complexity of our design solutions.

The Microsoft Spain team has some pretty good documentation on this philosophy of DDD, which is available for download here. Also a neat ASP.NET example of a n-tiered DDD application is available for download.

Closed Loop vs Open Loop Models in Card Processing

Found this good article on the internet that describes the differences between closed loop and open loop models.
Excerpts from the article:

"Open-loop payments networks, such as Visa and MasterCard, are multi-party and operate through a system that connects two financial institutions—one that issues the card to the cardholder, known as the issuing financial institution or issuer, and one that has the banking relationship with the merchant, known as the acquiring financial institution or acquirer—and manages information and the flow of value between them.
In a typical closed-loop payments network, the payment services are provided directly to merchants and cardholders by the owner of the network without involving third-party financial institution intermediaries. Closed-loop networks can range in size from networks such as American Express and Discover, which issue cards directly to consumers and serve merchants directly."


The site also has another interesting link on how companies such as American Express make money and the competitive advantage they gain because of the closed loop model.