NOTAM start life as messages on the Aeronautical Fixed System (AFS). They are received centrally at the UK NOTAM office at London Heathrow from originators within the UK and from foreign NOTAM offices. AIS staff check and edit the NOTAM if necessary and
they are then placed in the transmit queue for transmission to all UK NOTAM recipients. These include ATC offices, some airlines, briefing services etc.
There is no central world-wide NOTAM database, databases are built up individually by users from the incoming message stream. ICAO NOTAM format