Recommendation ITU-T X.501 | ISO/IEC 9594-2 provides a number of different models for the Directory as a framework for the other Recommendations in the ITU-T X.500-series. The models are the overall (functional) model, the administrative authority model, generic Directory Information models providing Directory User and Administrative User views on Directory information, generic Directory System Agent (DSA) and DSA information models and operational framework, and a security model.