Enterprise Library is a collection of reusable software components (application blocks) designed to assist software developers with common enterprise development challenges (such as logging, validation, caching, exception handling, and many others). Application blocks are a type of guidance encapsulating Microsoft recommended development practices; they are provided as source code, tests plus documentation that can be used "as is," extended, or modified by developers to use on complex, enterprise-level line-of-business development projects.

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