Reference Data Management (RDM) is a sub-system of Hermes.Core which implements the functionality and services related to Reference Data and Customs Authorities Management. The objective of RDM is to provide query services to other components through a centralised repository of a specified set of defined code lists. Each code list of the repository has mutable codes applicable to given periods of time. For each code list maintained in the repository, RDM provides management services allowing the addition of new codes, the editing of existing codes, and the editing of validity period applicable to each code. Deletion services are intentionally not provided. Once a code is created for specific code list, it cannot be deleted, but instead it can be updated to invalid.

Each code list is characterised by two attributes: its source and its contents. The source of a code list can be either national or of a common domain (eg EU). The national code lists can be directly updated by a customs agency, so the respective maintenance services are provided through the UI.

The second attribute characterising a code list is its contents. Normally, a code list will be a pair of value description pair, in which case the code list is termed as simple. In all other cases the code list is termed as complex.