You'll need a license to match the number of production servers that you want to connect to in SQL Data Catalog.
For example, you would require a 5-server license (the minimum) for the following scenario:
3 x production servers, 3 UAT servers, 2 development servers
If you don't want to classify or catalog all of the databases on the servers, you will still need a license to cover each of the servers on which they are deployed.
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