Recommendation ITU-T X.519 | ISO/IEC 9594-5 specifies the Directory Access Protocol, the Directory System Protocol, the Directory Information Shadowing Protocol and the Directory Operational Binding Management Protocol fulfilling the abstract services specified in Recommendation ITU-T X.501 | ISO/IEC 9594-2, Recommendation ITU-T X.511 | ISO/IEC 9594-3, Recommendation ITU-T X.518 | ISO/IEC 9594-4 and Recommendation ITU-T X.525 | ISO/IEC 9594-9. It includes specifications for supporting underlying protocols to reduce the dependency on external specifications.