SCD-2

SCD-2 stands for Slowly Changing Dimension, Type 2 — a data-warehousing pattern for storing values that change over time without losing the history. Each row gets a valid_from and valid_to timestamp; updating a value means writing a new row with the new value and closing out the previous row by setting its valid_to.

The alternative, SCD-1, is to overwrite the previous value in place. SCD-1 loses history; SCD-2 keeps it. For a publication that publishes claims about the world (“unemployment was 4.2% as of April 15”), SCD-2 is the correct choice — readers and AI agents can resolve “what did Thin Gold report on April 22?” by querying for the row whose valid_from <= '2026-04-22' AND valid_to > '2026-04-22'.

Thin Gold’s facts table is SCD-2. The current value for any fact is the row where valid_to IS NULL. The full history can be reconstructed for any fact_key by ordering on valid_from.