In recent years, the Italian Institute of Statistics (ISTAT) has increased the integration of statistical and non-statistical sources in order to improve data quality while reducing the burden on respondents. This process must comply with the GDPR (Regulation EU 2016/679). Therefore, ISTAT recently re-engineered the process of data pseudonymisation and the process of data release to internal users. As a result, ISTAT implemented the new Administrative and Statistical Microdata Management System (SIGMA). The main element of innovation is the definition of the Specific Integration Domains (SID); a SID is a designed area - accessible only to authorised persons - where only necessary data are present for a specific statistical purpose and for the time strictly necessary. SIGMA consists of a catalogue through which data availability can be consulted and data can be selected for statistical use. The correctness and consistency of the metadata in the catalogue is crucial, in order to make system work properly. In addition, the link between data and metadata allows the subsequent activation of operations necessary to perform statistical processing in the SIDs. The main purpose of SIGMA is to improve privacy protection maintaining statistical efficiency.