MSDN Magazine - February 2009 - (Page 46)

Best Practices An Introduction To Domain-Driven Design Dave Laribee Domain-Driven Design (DDD) is a collection of principles and patterns that help developers craft elegant object systems. Properly applied it can lead to software abstractions called domain models. These models encapsulate complex business logic, closing the gap between business reality and code. In this article, I’ll cover the basic concepts and design patterns germane to DDD. Think of this article as a gentle introduction to designing and evolving rich domain models. To provide some context to the discussion, I’m using a complex business domain with which I’m familiar: insurance policy management. If the ideas presented here appeal to you, I highly recommend that you deepen your toolbox by reading the book Domain-Driven Design: Tackling Complexity in the Heart of Software, by Eric Evans. More than simply the original introduction to DDD, it is a treasure trove of information by one of the industry’s most seasoned this article discusses: • Modeling from Ubiquitous Language • Bounded contexts and aggregate roots • Using the single responsibility Principle • repositories and databases software designers. The patterns and core tenets of DDD that I will discuss in this article are derived from the concepts that are detailed in this book. The Platonic Model technologies discussed: Visual studio 46 msdn magazine Since we’re just starting off here, it makes practical sense to define what I mean by model. Answering this question leads us on a short, metaphysical journey. Who better than Plato to guide us? Plato, that most famous student of Socrates, proposed that the concepts, people, places, and things we intuit and perceive with our senses are merely shadows of the truth. He dubbed this idea of a true thing a Form. To explain Forms, Plato used what’s become known as the allegory of the cave. In this allegory, there exists a people that are bound inside a deep, dark cave. These cave people are chained in such a way that they can only ever see a blank wall of the cave that receives light from the opening. When an animal walks by the opening, a shadow is projected onto the interior wall that the cave dwellers see. To the cave dwellers, these shadows are the real thing. When a lion walks by, they point at the shadow of the lion and exclaim, “Run for cover!” But it is really only a shadow of the real Form, the lion itself. You can relate Plato’s theory of Forms to DDD. Much of its guidance helps us get closer to the ideal model over time. The path to the Form you want to describe with your code is scattered about in

Table of Contents Feed for the Digital Edition of MSDN Magazine - February 2009

MSDN Magazine - February 2009 Contents Toolbox CLR Inside Out Data Points Cutting Edge Patterns In Practice Best Practices .Net Interop "Oslo" Basics Patterns Silverlight Under The Table Foundations Windows With C++ .NET Matters Going Places { End Bracket }

MSDN Magazine - February 2009

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