The MetadataExchange : is an open-source platform consisting of central "data catalogue" and a number of plugins that allow users to classify and describe the data that exists within their organization.
MetadataExchange makes data:
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Creating a central source-of-truth empowers knowledge workers to discover what's new, understand what's available and access the data they need when they need it.
To get started please see Starting Out - A quick look around
For some specific how-to articles please read How-To Articles
And to understand the core concepts in the MDX please see Key Concepts