Industry Standing Data (ISD) is a new set of standardized data required by Market Participants, introduced by the Market-wide Half-Hourly Settlement (MHHS) Programme. It is designed to replace the legacy Market Domain Data (MDD).
The ISD includes some entities from the existing MDD and introduces new entities specific to MHHS. Entities related to Non-Half Hourly Settlement will not be included in the ISD. During a transitional period, the ISD will coexist with the MDD until the latter is retired.
ISD is managed with version control, updated monthly, and follows a new method for raising changes and a governance process. This includes the publication and data retrieval mechanisms, which differ from the MDD. The ISD data set includes 34 entities, referred to as the ISD Catalogue, each with a specific purpose and format, and all data will be provided in CSV format.

Line Loss Factors (LLFs) are a component of the Industry Standing Data (ISD) introduced by the MHHS Programme. LLFs are now considered part of the overall ISD dataset, which is replacing the legacy Market Domain Data (MDD).
LLFs represent the amount of electricity lost due to the resistance of the transmission and distribution networks. These losses are accounted for when measuring and settling the electricity consumption or generation of different market participants. In the ISD context, LLFs will continue to serve their purpose of adjusting the measured consumption or generation volumes for these network losses.
The LLF data will be included in the ISD Catalogue and will be available in CSV format. The LLFs are managed and provided as part of the overall ISD process, ensuring that all Market Participants use a consistent and standardized set of data. Updates to LLFs, like other ISD entities, will be managed via a new governance process and published monthly in line with the ISD release schedule.

Market Domain Data (MDD) is the current set of standardized data used by Market Participants in the UK electricity market. MDD includes various entities that define and support the market's operations, such as data about market participants, their roles, and specific market configurations. This data set is essential for electricity settlement and is widely used across the industry to ensure all participants use consistent data.
As part of the Market-wide Half-Hourly Settlement (MHHS) Programme, MDD is being replaced by the new Industry Standing Data (ISD). The transition means that some of the existing MDD entities will be carried over into the ISD, while others, particularly those related to Non-Half Hourly Settlement, will not be included in the new data set.
During the transition period, MDD will coexist with ISD. This allows for a phased approach where market participants can adapt to the new data standards and processes introduced by ISD. Eventually, MDD will be completely phased out, and all data requirements will be managed under the ISD framework.
For more information and to view the current MDD data, you can visit the MDD Viewer on the Elexon Portal