Feb 08, 2016
First of all, let me emphasize that the Patterns in Action is a collection of patterns that demonstrate the power of design patterns in modern day application architecture.
It is not necessarily the best architecture to build an application. For that we offer SPARK, which is our recommended platform for building robust and very fast.NET solutions.
Going back to your question:
Yes, Patterns in Action is a loosely coupled architecture. The solution demonstrates that any Presentation Layer (e.g. ASP.NET Forms, MVC, WPF, Windows Apps, etc) can run against the exact same Repository and DAL (Data Access Layer). The DAL, in turn, is configurable to use any Provider: ADO.NET, Entity Framework, or LINQ to SQL. Finally,any of these Providers can be configured to run against any database, such as MS Access, SQL Server, or ORACLE.
It is only through a decoupled architecture that this flexibility can be accomplished.
In a real-world scenario this flexibility is not really required and projects typically pick just one Presentation Layer, one Data Access Provider, and one Database. For example MVC, Entity Framework, and SQL Server. Or WPF, ADO.NET, and ORACLE. Once built, it is highly unusual for an application to change Presentation Layer, Data Provider, or Database.
Hope this helps.