The models defined in this Recommendation | International Standard 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.
This Recommendation | International Standard provides a specialization of the generic Directory Information Models to
support Directory Schema administration.
The other ITU-T Recommendations in the X.500 series | parts of ISO/ IEC 9594 make use of the concepts defined in this
Recommendation | International Standard to define specializations of the generic information and DSA models to provide
specific information, DSA and operational models supporting particular directory capabilities (e.g., Replication):
a) the service provided by the Directory is described (in Rec. ITU-T X.511 | ISO/ IEC 9594-3) in terms of the
concepts of the information framework: this allows the service provided to be somewhat independent of
the physical distribution of the DIB
b) the distributed operation of the Directory is specified (in Rec. ITU-T X.518 | ISO/ IEC 9594-4) so as to
provide that service, and therefore maintain that logical information structure, given that the DIB is in fact
highly distributed
c) replication capabilities offered by the component parts of the Directory to improve overall Directory
performance are specified (in Rec. ITU-T X.525 | ISO/ IEC 9594-9).
The security model establishes a framework for the specification of access control mechanisms. It provides a mechanism
for identifying the access control scheme in effect in a particular portion of the Directory Information Tree (DIT), and it
defines three flexible, specific access control schemes which are suitable for a wide variety of applications and styles of
use. The security model also provides a framework for protecting the confidentiality and integrity of directory operations
using mechanisms such as encryption and digital signatures. This makes use of the framework for authentication defined
in Rec. ITU-T X.509 | ISO/ IEC 9594-8 as well as generic upper layers security tools defined in Rec. ITU-T X.830 |
ISO/ IEC 11586-1.
DSA models establish a framework for the specification of the operation of the components of the Directory. Specifically:
a) the Directory functional model describes how the Directory is manifested as a set of one or more
components, each being a DSA
b) the Directory distribution model describes the principals according to which the DIB entries and
entry-copies may be distributed among DSAs
c) the DSA information model describes the structure of the Directory user and operational information held
in a DSA
d) the DSA operational framework describes the means by which the definition of specific forms of
cooperation between DSAs to achieve particular objectives (e.g., shadowing) is structured.
© ISO/ IEC 2020 – All rights reserved

ISO/ IEC 9594-2:2020 (E)
2 Rec. ITU-T X.501 (10/ 2019)