UDL is an extension of files characteristic for operating systems from the Windows family. These files are used to define connections with remote data sources, e.g. with SQL databases. You can specify the type of data provider, server address, login and password, or specify the appropriate database on the server.

Technically, UDLs are plain text files and can be previewed in any editor. However, to edit such a link it is much more convenient to display the file properties, where you can easily define the connection parameters.