Lego the interlocking construction brick system for kids provides a perfect example of simple but extremely powerful interface design, as you can build virtual any things from its basic but reusable building blocks.<br/> As Lego provides a perfect example for good interface design it will be used for comparison for software architectural theory and design patterns for reusable and maintainable application like "Keep it simple stupid" (KISS), the power of contracts /interfaces, Separation of Concerns (SoC),"Don’t Repeat Yourself" (DRY),"You Ain't Gonna Need It" (YAGNI), “Inversion of Control” including Dependency Injection and Service Locator.

Lego bricks are not just a collection of pieces; instead they provide a platform to build on whatever can be imagined. Within this session the previously discussed Lego principle will be applied on an example application based on examples different technologies and platforms for reusable software. Unity, Managed Extensibility Framework (MEF) and Windows Communication Foundation (WCF) will be examined and compared as such platforms to build on.