Overview Application blocks help address the common problems that developers face from one project to the next. They are designed to encapsulate the Microsoft recommended best practices for .NET-based applications. In addition, they can be added to .NET-based applications quickly and easily. For example, the Data Access Application Block provides access to the most frequently used features of
ADO.NET 2.0 in simple-to-use classes, thus boosting developer productivity. It also addresses scenarios not directly supported by the underlying class libraries. Different applications have different requirements, and you will not find that every application block is useful in every application that you build. Before using an application block, you should have a good understanding of your application requirements and of the scenarios that the application block is designed to address.
Enterprise Library–January 2006 contains the following general purpose application blocks: Enterprise Library also includes a set of core functions, including configuration, instrumentation, and object builder services. These functions are used by all other application blocks.
Get more details, download the Enterprise Library for .NET Framework 2.0 and other relater resources from here: http://msdn2.microsoft.com/en-us/library/aa480453.aspx
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Sreenath