Microsoft Enterprise Library 4.0

Application Block	Purpose	Comments
Cache	To improve the application performance by incorporating local cache in the application.	Supports In-memory, database storage or isolated storage. Has the functionality needed to retrieve , add and remove cached data.
Cryptography	To incorporate cryptographic functionality in the application	Used to encrypt information, creating a hash from data and comparing hash values to verify that the values has not been altered
Data Access	To implement common data access functionality	Used in various situations such as reading data for display, passing the data through application layer and submitted data back to the database system. The application block includes classes that are specific to SQL Server and Oracle
Exception Handling	Helps developers and policy makers to create a consistent strategy for processing exceptions that occur in all architectural layers of an enterprise application	Define and maintain the rules at administrative level i.e. maintain and modify rules that govern exception handling without changing the application block code.
Logging	To implement the logging functionality easily	Log the information at various locations The event log An e-mail message A database A message queue A text file A Windows Management Instrumentation (WMI) event Custom locations using application block extension points
Security	To implement the common authorization related functionality	To support authorization and to cache the user’s authorization and authentication data. Together with .Net framework 2.0 functionality developers can easily implement common security related functionality. Supports custom implementations of security providers.
Validation	To implement the structured and easy-to-maintain validation scenarios.	Includes adaptors that allows you to use application blocks with the following technology. ASP.Net Windows Forms WCF
Policy injection	Provides a mechanism for automatically applying policies to object instances; this helps developers to better manage crosscutting concerns, maximize separation of concerns, and encapsulate behavior	Developers define the set of policies for the target classes and their members through configuration of the Policy Injection Application Block or by applying attributes to individual members of the target class.
Unity	Lightweight, extensible dependency injection container with support for constructor, property, and method call injection	Used to generate both Enterprise Library objects and your own custom business objects.