Shared Order Book (SOB)
The Shared Order Book is the central order-book component of SIDC. Orders submitted through different NEMOs are pooled into the shared book so they can match across NEMOs and bidding zones when compatible orders and enough transmission capacity exist. It prevents intraday liquidity from fragmenting by exchange or country.
The Shared Order Book (SOB) is the central order-book component of Single Intraday Coupling. Orders submitted by market participants through different NEMOs are pooled into the shared book so they can match across NEMOs and across bidding zones when compatible orders and transmission capacity exist.
How it fits into SIDC
SIDC continuous trading relies on three common systems: the Shared Order Book, the Capacity Management Module and the Shipping Module. The SOB handles available orders; the capacity module tracks remaining cross-border capacity; the shipping module turns concluded trades into information for NEMOs, TSOs, central counterparties and shipping agents.
Why it matters
Without the SOB, intraday liquidity would be fragmented by exchange and country. With it, an Estonian order submitted through Nord Pool can match against compatible liquidity elsewhere in the coupled SIDC area, provided there is enough cross-zonal capacity. This is why intraday trading can repair forecast errors across borders rather than only inside one national order book.