ISO/IEC 9594-2:2017

The models defined in ISO/IEC 9594-2:2017 provide a conceptual and terminological framework for the other ITU-T X.500-series Recommendations | parts of ISO/IEC 9594 which define various aspects of the Directory.
The functional and administrative authority models define ways in which the Directory can be distributed, both functionally and administratively. Generic Directory System Agent (DSA) and DSA information models and an Operational Framework are also provided to support Directory distribution.
The generic Directory Information Models describe the logical structure of the Directory Information Base (DIB) from the perspective of Directory and Administrative Users. In these models, the fact that the Directory is distributed, rather than centralized, is not visible.  
ISO/IEC 9594-2:2017 provides a specialization of the generic Directory Information Models to support Directory Schema administration.