An important role of the SBR is to maintain and to keep track of changes in statistical units and their characteristics that occur in the economy. Maintenance is a continuous process in which constant modifications of the set of statistical units occur over time. The extent of the modifications depends on the update strategy of the SBR. In this respect the SBR is considered to be a live register in which the composition and characteristics of units constantly change over time.The live register is a vehicle for bringing together data from the various sources that provide the basis for derivation of statistical units. It is the starting point for communications with the owners of the sources and for discussions about units. Legal units are usually the building blocks for creating statistical units. In some countries the SBR is the only environment in which legal units of all forms are brought together. Statistical units are created in the live register.