The SIRUS statistical register is the main source for the SIDE system. In particular, it provides the statistical variables used to delimit the scope of business demography, such as whether legal units are producers or belong to the market sector.

Although transmitted by SIRUS, a significant proportion of the data used by SIDE comes from the Sirene administrative register (Système Informatique pour le Répertoire des Entreprises et de leurs Établissements). This includes identification data, such as the unique identifier assigned to legal entities and natural persons (the Siren number) and to each of their establishments (the Siret number), as well as data on the administrative status of units in the register, enabling the identification of business births and business deaths.