As part of the SDI Standard Operating Procedures data gets harmonized for viewing and filtering purposes.
Data harmonization uses expert/scientist input to map existing metadata (parameter names, method/device information, unit strings) to a standard vocabulary (esp. NERC). This process is referred to as Mapping.
This presentation explains how the Mapping principle works.
The Status Quo of Mapping Tables and Statistics can be found in DAM/MareHUB space.