A SSDSID code is a unique identifier used to match and reconcile trades between parties in the settlement process.
SSDSID is specified by CpML and stands for System Static Data Standard Identifier. It was defined by EFET to facilitate eSM. This code had been specified to provide for cases where ie. the EIC is used for two separate legal entities.
It is the unique identifier of counterparties in the OTC energy market according to the EFET eSM standard. It's a combination of the VAT ID and EIC, separated by an underscore.
This allows to identify which company is trading and which entity of the company is involved. e.g.: DE123456789_11XTRADER------P
Ideally, the combination of the VAT ID and the EIC code within the SSDSID are the identifiers for the same legal entity, however, this is not mandatory and not even always possible. The VAT ID used in the SSDSID might differ from the VAT ID used in the customer or supplier data.
In general, each legal entity using eSM can define its SSDSID independently.