1. Introduction

   In the late 1980s, X.500 Directory Services were standardized by the
   CCITT (Commite' Consultatif International de Telegraphique et
   Telephonique), now a part of the ITU (International Telephone Union).
   This lead to Directory Service piloting activities in the early
   1990s, including the COSINE (Co-operation and Open Systems
   Interconnection in Europe) PARADISE Project pilot [COSINEpilot] in
   Europe.  Motivated by needs for large-scale directory pilots, RFC
   1274prop(-> 4524prop) was published to standardize the directory schema and naming
   architecture for use in the COSINE and other Internet X.500 pilots
   [RFC1274].

   In the years that followed, X.500 Directory Services have evolved to
   incorporate new capabilities and even new protocols.  In particular,
   the Lightweight Directory Access Protocol (LDAP) [RFC4510] was
   introduced in the early 1990s [RFC1487], with Version 3 of LDAP
   introduced in the late 1990s [RFC2251] and subsequently revised in
   2005 [RFC4510].

   While much of the material in RFC 1274prop(-> 4524prop) has been superceded by
   subsequently published ITU-T Recommendations and IETF RFCs, many of
   the schema elements lack standardized schema descriptions for use in
   modern X.500 and LDAP directory services despite the fact that these
   schema elements are in wide use today.  As the old schema
   descriptions cannot be used without adaptation, interoperability
   issues may arise due to lack of standardized modern schema
   descriptions.

   This document addresses these issues by offering standardized schema
   descriptions, where needed, for widely used COSINE schema elements.

1.1. Relationship to Other Documents

   This document, together with [RFC4519] and [RFC4517], obsoletes RFC
   1274prop(-> 4524prop) in its entirety.  [RFC4519] replaces Sections 9.3.1 (Userid) and
   9.3.21 (Domain Component) of RFC 1274prop(-> 4524prop).  [RFC4517] replaces Section
   9.4 (Generally useful syntaxes) of RFC 1274prop(-> 4524prop).

   This document replaces the remainder of RFC 1274prop(-> 4524prop).  Appendix A
   discusses changes since RFC 1274prop(-> 4524prop), as well as why certain schema
   elements were not brought forward in this revision of the COSINE
   schema.  All elements not brought are to be regarded as Historic.

   The description of the 'domain' object class provided in this
   document supercedes that found in RFC 2247prop.  That is, Section 3.4 of
   this document replaces Section 5.2 of [RFC2247].

   Some of the schema elements specified here were described in RFC 2798
   (inetOrgPerson schema).  This document supersedes these descriptions.
   This document, together with [RFC4519], replaces Section 9.1.3 of RFC
   2798.

1.2. Terminology and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14 [RFC2119].

   DIT stands for Directory Information Tree.
   DN stands for Distinguished Name.
   DSA stands for Directory System Agent, a server.
   DSE stands for DSA-Specific Entry.
   DUA stands for Directory User Agent, a client.

   These terms are discussed in [RFC4512].

   Schema definitions are provided using LDAP description formats
   [RFC4512].  Definitions provided here are formatted (line wrapped)
   for readability.