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Versions: 00 01                                                         
INTERNET-DRAFT                                                  C. Apple
<draft-ietf-schema-rqmts-list-01.txt>                          AT&T Labs
Expires: October 21, 1998                                  21 April 1998

Requirements for the Initial Release of a Directory Schema Listing Service

Status of this Memo

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
   Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
   munnari.oz.au (Pacific Rim), or ftp.isi.edu (US West Coast).


   This memo documents requirements for listing directory services
   schema in a centrally operated, administered, and maintained
   repository. This repository will be available as a resource to
   directory protocol and service implementors to facilitate schema

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                             Table of Contents

   1.0 Introduction . . . . . . . . . . . . . . . . . . . . .  3
   1.1 Scope. . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.2 Terms and Definitions. . . . . . . . . . . . . . . . .  4
   1.3 Usage Scenarios. . . . . . . . . . . . . . . . . . . .  5
   1.3.1 Location/Retrieval of the vCard Schema for LDAPv3. .  5
   1.3.2 Submission of a New Schema Listing via SMTP. . . . .  5
   2.0 Listing Service Requirements . . . . . . . . . . . . .  6
   2.1 Functional Requirements. . . . . . . . . . . . . . . .  6
   2.2 Operational Requirements . . . . . . . . . . . . . . .  6
   2.3 Repository Access Functionality. . . . . . . . . . . .  7
   3.0 Listing Service Namespace Requirements . . . . . . . .  8
   4.0 Listing Requirements . . . . . . . . . . . . . . . . .  8
   5.0 Listing Storage Requirements . . . . . . . . . . . . .  9
   6.0 Security Considerations. . . . . . . . . . . . . . . .  9
   6.1 Compromisable Assets . . . . . . . . . . . . . . . . .  9
   6.2 Attack Scenarios . . . . . . . . . . . . . . . . . . .  9
   6.2.1 Denial-of-Service Attack Scenarios . . . . . . . . . 10
   6.2.2 Confuse-the-User Attack Scenarios. . . . . . . . . . 10
   6.3 Security Requirements on Schema Listing Procedures . . 10
   7.0 Acknowledgements . . . . . . . . . . . . . . . . . . . 11
   8.0 References . . . . . . . . . . . . . . . . . . . . . . 12
   9.0 Author's Address . . . . . . . . . . . . . . . . . . . 13

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1.0 Introduction

   The fastest route to interoperable directory services is through
   standard object classes and attribute types. There is a growing
   number of places where schema for Internet Directory Services and
   Internet Operations are being defined, with varying degrees of
   documentation.  This plethora of schema is unavoidable in the light
   of the needs of different service communities, but it makes it
   difficult for directory service builders to find and make use of an
   existing schema that will serve their needs and increase
   interoperability with other systems. A listing service providing a
   single point of discovery for directory service schema will promote
   schema reuse, reduce duplication of effort, and thus promote
   directory service interoperability.

   The intent is to offer a schema listing service with public read
   access and restricted, moderated write access. Many hard-coded
   choices and constraints have been reflected in this requirements
   document for the purpose of expediting deployment. Future releases of
   the service may require an update of this document.

   Initially, such a listing service will be centrally operated,
   administered, and maintained. The schema listing repository database
   may also be mirrored to ensure some level of redundancy for read
   access in the event of service interruption. Eventually, the
   operations, administration, and maintenance of such a listing service
   may evolve to use a more distributed deployment scenario.

   The schema listing service is also intended to be largely automated,
   with minimal human involvement. Human involvement is likely to be
   limited to the following types of activities:

      + handling repository access problems
      + trouble resolution for computing and communications facilities
      + dealing with reasonable requests that fall outside
        of the scope of normal schema listing repository operations
      + reviewing schema listing requests on a mailing list
        prior to publishing in the listing repository

   Future releases of the service may automate some of these tasks.

1.1 Scope

   Requirements for the initial release of a directory schema listing
   service are inside the scope of this document.

   Specifications for syntaxes and grammars to be used in the initial
   release of the directory schema listing service are outside the scope

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   of this document.

   Documentation of schema listing procedures is outside the scope of
   this document.

1.2 Terms and Definitions

   Information Object - a descriptive abstraction of some real-world

   Object Attribute - a descriptive property of an information object;
   typically, object attributes are defined in terms of semantic and
   syntactic definitions

   Schema - a collection of definitions for related information objects

   Schema Unit - a related or grouped set of object attributes that form
   a discrete unit within the context of a schema for a particular
   protocol; examples include an LDAP object class or a WHOIS++ template

   Schema Pak - a related or grouped set of schema units that
   collectively specify a schema associated with a particular protocol;
   an example of a schema pak is the set of LDAP object classes
   specified in [RFC2256]

   Metadata - characteristics that differentiate one schema unit or
   schema pak from another; used to catalog listing service content;
   structured using a profile of [MIMEDIR]; also contains references to
   files stored within and outside of a listing repository

   Schema Unit Content - a formal specification of a schema unit using a
   profile of [MIMEDIR]

   Schema Unit Listing - the combination of a single schema unit content
   file intended for use within the context of a particular protocol and
   a file containing metadata describing the schema unit specified
   within that schema unit content file

   Schema Pak Listing - a single metadata file containing information
   describing and referring to a set of related or grouped schema unit
   content files

   Repository - a database in which listings are stored

   Listing Request - a proposed schema unit listing or schema pak
   listing formatted using [MIME] constructs that is submitted for
   consideration as a listing to be published in a repository

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   Operator - an organization that administers and maintains a

   Primary Repository - the repository that masters the schema listings

   Shadow Repository - a repository that mirrors the primary repository

   Contact Person - the name of the individual who holds the authority
   to update a listing and who should be contacted if questions or
   concerns arise related to a listing or listing request

   Listing Authority Contact - the name of the individual who holds
   authority to replace a contact person; can be either the contact
   person for a listing or an alternate contact within the organization
   to which the contact person belongs (this allows one person
   organizations to list schema)

   The terms for specifying requirement level defined in [RFC2119] are
   used in this document.

1.3 Usage Scenarios

1.3.1 Location/Retrieval of the vCard Schema for LDAPv3

   A user of the schema listing service wants to locate a copy of the
   vCard schema for LDAPv3 [RFC2251] so that they can use it in a
   prototyping project. First, they point their web browser at a schema
   listing repository web site and download the list of available
   schema.  Next, they use the search command on their browser to locate
   occurances of the string "vCard". The browser automatically scrolls
   down to the appropriate place in the list of available schema and the
   user clicks on a link to view the listing metadata to verify that
   this is indeed the vCard schema for use with version 3 of the LDAP
   protocol. Included in the web-based representation of the listing
   metadata are ftp URLs pointing to available profiles containing
   listing content for this schema.  The user clicks on the link for the
   profile that they can use.

1.3.2 Submission of a New Schema Listing via SMTP

   A schema writer wishes to list a schema they have created and
   prepares the listing metadata and listing content according to one or
   more appropriate [MIMEDIR] profiles. The schema writer will obtain a
   permanent, unique schema listing name for the request.

   The schema writer sends an SMTP message including the listing meta
   data and all available listing content in multipart-related [MIME]

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   format to a listing request review mailing list. After a short review
   period, the listing repository operator validates the request, and if
   properly formed, publishes the listing according to the listing
   procedures. An announcement of the newly published schema listing is
   sent to a mailing list reserved for this purpose.

2.0 Listing Service Requirements

2.1 Functional Requirements

   Listed schema MAY be published as an RFC.

   A list of available listings MUST be maintained.

   Listings MUST be named according to the namespace requirements
   defined in section 3.

   The listing service SHALL maintain information about schema units,
   beyond their definition. This information is referred to as metadata
   and will consist of information used for cataloging listings in the
   repositories.  The particular set of  metadata elements used during
   the initial deployment of the listing service will be defined in
   other documents.

   Listing metadata and listing content MUST be parsable.

2.2 Operational Requirements

   The process of listing schema MUST be centralized for the initial

   All versions of all listings MUST be retained. A simple method for
   getting the most recent version of a particular listing MUST be

   The contact person for a listing MAY give an earlier listing a higher
   version number, or MAY request that the listing get a new name.

   The listing repository MUST be centrally administered.

   The listing repository MAY be mirrored.

   The primary repository operator MUST obtain an OID subtree for which
   they hold sub-allocation authority for use in the schema listing

   Listing requests MAY be signed using PGP/MIME as described in
   [RFC2015]. The primary listing repository operator MUST be able to

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   accept schema listing requests in PGP/MIME messages, although they
   are NOT REQUIRED to validate the signatures. The method for
   validating and determining trust of signatures is outside the scope
   of this document and is determined by the parties in the exchange.
   The method for determining and validating trust in an unsigned
   request is outside the scope of this document, as is the method for
   determining trust in schema listing repository or its content.

   A mailing list MUST be created for the purpose of submitting listing
   requests for review prior to publishing in the schema listing
   repository. The schema listing repository publication process MUST be
   moderated via this mailing list. Listing requests MUST be subjected
   to community review on this mailing list for a period of at least 2
   weeks. If no comments are received, properly formed schema listing
   requests SHALL be published as listings; otherwise, the request MAY
   either denied or the listing MAY published subject to incorporation
   of comments.

   A mailing list MUST be created for announcing new and updated

   A mailbox MUST be created for the purpose of receiving service
   trouble requests from users.

   Listing repository operators (of primary and shadow sites) MUST
   provide a free means of accessing the listing service consistent with
   the functionality documented in paragraph 2.3.

2.3 Repository Access Functionality

   The following schema listing repository access protocols MUST be
   supported:  FTP [RFC959], HTTP 1.1 [RFC2068], and SMTP [RFC821].

   The following access functions are REQUIRED:

      a) browse and retrieve schema unit content,
         metadata, and a list of available listings:

         + via HTTP requests

         + via FTP clients

         + via requests through an SMTP server

      b) search a list of available listings:

         + via HTTP, retrieving either HTML or text listings
           that can then be searched by the requestor

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         + via HTTP by accessing repository-based searching
           facilities such as keyword searching; this can
           return listing names, schema unit listings,
           schema pak listings, metadata, or other useful

      c) add and update listings by submitting a formatted
         request to a mailing list for community review:

         + via SMTP using appropriate MIME constructs
           as described in section 4.0

   Other access functions, including the following, MAY be supported,
   but will be defined in other documents in the future:

      a) search schema unit content

      b) search metadata

3.0 Listing Service Namespace Requirements

   The listing service namespace MUST be protocol-independent.

   The listing service namespace SHALL be based on OIDs.

   Listing names:

      + MUST be permanent

      + MUST be globally unique

      + MUST be publicly available

      + MUST NOT be recycled or re-used

      + MUST be created within the OID subtree reserved for use
        in the schema listing service and administered by the
        primary listing repository operator

4.0 Listing Requirements

   Schema unit content SHALL be limited to the information actually
   required to specify and encode the schema for storage and transfer.

   Metadata SHALL be composed of information used to catalog listings.

   Metadata element syntax SHALL be defined based on the concept of
   tagged attribute type-value pairs.

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   Language tags as specified in [RFC1766] MUST be used in all listings.

   Metadata element values MUST be encoded using the UCS Transformation
   Format - 8 bit form [RFC2044].

   For the purposes of submitting a listing request, schema unit content
   and metadata SHOULD be structured according to appropriate profiles
   of [MIMEDIR] defined in other documents.

   Content associated with a listing, but not stored in the schema
   listing repository (such as large copyright notices and vendor logo
   images) MAY be included by reference in the metadata. If such
   external references are included in a particular schema listing, a
   fingerprint of the external content generated prior to schema listing
   request creation MUST be included along with these references in the
   request. Details associated with the creation of these external
   content references, including the algorithm to be used for generation
   of a content fingerprint and the syntax of the reference, will be
   defined in the [MIMEDIR] profile used to format and encode listing
   metadata for storage and transfer.

5.0 Listing Storage Requirements

   Listing repository file names MUST be permanent, globally unique, and
   publicly available.

   Listing repository file names SHOULD be constructed in a manner that
   allows human and machine users to determine the nature of file
   content by inspecting the file names.

   Schema unit content and metadata MUST be stored in separate files.

6.0 Security Considerations

6.1 Compromisable Assets

   One or more of the following assets could be compromised if the
   service is attacked:

      + Metadata
      + Schema unit content
      + Repository Hardware & Software
      + Networking Facilities Connecting Repository to the Internet
      + Repository Mirror Sites

6.2 Attack Scenarios

Allowable methods for submitting listing requests are:

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      a) sending an e-mail message to a mail box

      b) submitting requests using web-based forms

Based on these request submission methods, there are a number of known
repository attack scenarios that must be considered during the
implementation of schema listing procedures and the software and
operational processes required to support them.

6.2.1 Denial-of-Service Attack Scenarios

Scenario A: someone could send in a large number of improperly formed

Scenario B: someone could send in a large number of properly formed, but
frivolous, useless, or trivial requests

6.2.2 Confuse-the-User Attack Scenarios

Scenario A: someone could send in a large number of valid, but
frivolous, useless, or trivial requests and some or all of these
requests actually become listings in the repository

Scenario B: someone could maliciously submit one or more slightly
modified versions of existing listings which are popular or widely used

6.3 Security Requirements on Schema Listing Procedures

The following contextual definitions apply to the requirements listed in
the remainder of this paragraph:

Verification - a process of determining authenticity of facts implied or
explicitly specified by a contact person during the process of
submitting a schema listing request; the methods used to implement such
a process MAY or MAY NOT be based on an IETF-sanctioned security
protocol; specification of the methods used to implement such a process
as well as the trust relationships relevant to the process are outside
the scope of this document.

High-Quality Directory Schema - a directory schema that serves some
useful purpose (e.g., a related set of attribute and object class
definitions for holding information about people in a LDAP directory); a
schema that is _not_ merely trivial or frivolous (e.g., a trivial schema
might consist of a related set of attribute and object class definitions
for holding information about the two possible binary bit values in a

The schema listing procedures SHOULD be designed to enable:

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      a) verification that all properly formed schema
         listing requests are submitted by the contact
         person claiming to originate them

      b) methods of ensuring that only properly-formed,
         high-quality directory schema are published
         in the schema listing repository

      c) verifcation that requests to change the identity
         of the contact person for a listing originate
         from the listing authority contact or the contact

      d) coping with the situation in which the contact
         person and/or listing authority contact for
         a schema is no longer available or is unable
         to submit updates to the listing
         for which they hold update authority

   For the initial release of the service, there is NO REQUIREMENT on
   any participant, user, or application to retain signature information
   as it applies to an entire schema listing request.

   Fingerprints included with external content reference metadata
   elements MUST be retained and included in published listing request.
   Users of the schema listing service SHOULD verify that fingerprints
   of referenced content match corresponding fingerprints included with
   external references as a part of the published schema listing.  If
   purported (included in the listing) and actual (computed by the user)
   fingerprints are different, users of the service SHOULD consider the
   possibility that the referenced content has changed since publication
   of the schema listing and that such a change could affect the way in
   which associated content can be used.

   Referenced content is outside of the control of the schema listing
   service.  A caveat explaining this concept MUST be included in the
   metadata of all published listings if external references are
   included in corresponding listing requests.

7.0 Acknowledgements

   Leslie Daigle of Bunyip Information Systems and Chris Weider of
   Microsoft provided valuable comments on multiple versions of this

   The engineering team for listing service requirements:

      Chris Apple - AT&T Labs

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      Sanjay Jain - Oracle
      Michael Mealling - NSI
      John Strassner - Cisco
      Sam Sun - CNRI
      Mark Wahl - Critical Angle
      Chris Weider - Microsoft

   Paul Hoffman, for review and comment during his effort to implement
   the primary directory schema listing service platform.

   The members of the ietf-schema-reg@imc.org mailing list.

8.0 References

   [CHARSET] Internet Assigned Numbers Authority, "CHARACTER SETS",

   [MIME] [RFC2045], [RFC2046], and [RFC2047].

   [MIMEDIR] T. Howes, M. Smith, "A MIME Content-Type for Directory
   Information", INTERNET-DRAFT <draft-ietf-asid-mime-direct-04.txt>,
   July 1997.

   [RFC821] J. Postel, "Simple Mail Transfer Protocol", RFC 821, August

   [RFC959] J. Postel, J.K. Reynolds, "File Transfer Protocol", RFC 959,
   October 1985.

   [RFC1630] T. Berners-Lee, "Universal Resource Identifiers in WWW",
   RFC 1630, June 1994.

   [RFC1766] H. Alvestrand, "Tags for the Identification of Languages",
   RFC 1766, March 1995.

   [RFC2015] M. Elkins, "MIME Security with Pretty Good Privacy (PGP)",
   RFC 2015, October 1996.

   [RFC2044] F. Yergeau, "UTF-8, a transformation format of Unicode and
   ISO 10646", RFC 2044, October 1996.

   [RFC2045] N. Freed, N. Borenstein, "Multipurpose Internet Mail
   Extensions (MIME) Part One: Format of Internet Message Bodies", RFC
   2045, November 1996.

   [RFC2046] N. Freed & N. Borenstein, "Multipurpose Internet Mail
   Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996.

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   [RFC2047] K. Moore, "MIME (Multipurpose Internet Mail Extensions)
   Part Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
   November 1996.

   [RFC2068] R. Fielding, J. Gettys, J. Mogul, H. Frystyk, T. Berners-
   Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, January

   [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
   Requirement Level", RFC 2119, March 1997.

   [RFC2251] M. Wahl, T. Howes, S. Kille, "Lightweight Directory Access
   Protocol (Version 3)", RFC 2251, December 1997.

9.0 Author's Address

   Chris Apple
   AT&T Labs
   600 - 700 Mountain Ave., Room 2F-165
   Murray Hill, NJ 07974-0636

   E-Mail: capple@att.com
   Phone: +1 908 582 2409
   FAX: +1 908 582 3296

             This INTERNET-DRAFT expires on October 21, 1998.

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