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Versions: 02 RFC 1837

Network Working                                  S.E. Hardcastle-Kille
Group                                                 ISODE Consortium
INTERNET-DRAFT                                           November 1992
                                                   Expires:  June 1993

          Representing Tables and Subtrees in the Directory



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.
Internet Drafts may be updated, replaced, or obsoleted by other
documents at any time.  It is not appropriate to use Internet Drafts
as reference material or to cite them other than as a "working draft"
or "work in progress."

Please check the I-D abstract listing contained in each Internet Draft
directory to learn the current status of this or any other Internet
Draft.
Abstract
This document defines techniques for representing two types of
information mapping in the OSI Directory [CCI88].


1.  Mapping from a key to a value (or set of values), as might be done
    in a table lookup.

2.  Mapping from a distinguished name to an associated value (or
    values), where the values are not defined by the owner of the
    entry.  This is achieved by use of a directory subtree.

This techniques were developed for supporting MHS use of Directory
[HK92], but are specified separately as they have more general
applicability.

This draft document will be submitted to the RFC editor as a protocol
standard.  Distribution of this memo is unlimited.  Please send
comments to the author or to the discussion group
<mhs-ds@mercury.udev.cdc.com>.




INTERNET--DRAFT           Representing Subtrees          November 1992


1  Representing Flat Tables

Before considering specific function, a general purpose technique for
representing tables in the directory is introduced.  The schema for
this is given in Figure 1.
A table can be considered as an unordered set of key to (single or
multiple) value mappings, where the key cannot be represented as a
global name.  There are four reasons why this may occur:


1.  The object does not have a natural global name.

2.  The object can only be named effectively in the context of being a
    key to a binding.  In this case, the object will be given a
    natural global name by the table.

3.  The object has a global name, and the table is being used to
    associate parameters with this object, in cases where they cannot
    be placed in the objects global entry.  Reasons why they might not
    be so placed include:

     o  The object does not have a directory entry

     o  There is no authority to place the parameters in the global
        entry

     o  The parameters are not global --- they only make sense in the
        context of the table.

4.  It is desirable to group information together as a performance
    optimisation, so that the block of information may be widely
    replicated.

A table is represented as a single level subtree.  The root of the
subtree is an entry of object class Table.  This is named with a
common name descriptive of the table.  The table will be located
somewhere appropriate to its function.  If a table is private to an
MTA, it will be below the MTA's entry.  If it is shared by MTA's in an
organisation, it will be located under the organisation.

The generic table entry contains only a description.  All instances
will be subclassed, and the subclass will define the naming attribute.
Two subclasses are defined:


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_______________________________________________________________________
table OBJECT-CLASS
    SUBCLASS OF top
    MUST CONTAIN {commonName}
    MAY CONTAIN {manager}
    ::= oc-table


tableEntry OBJECT-CLASS
    SUBCLASS OF top
    MAY CONTAIN {description}                                       10
    ::= oc-table-entry

textTableEntry OBJECT-CLASS
    SUBCLASS OF tableEntry
    MUST CONTAIN {textTableKey}
    MAY CONTAIN {textTableValue}
    ::= oc-text-table-entry

textTableKey ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX                                           20
        caseIgnoreStringSyntax
    ::= at-text-table-key

textTableValue ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX
        caseIgnoreStringSyntax
    ::= at-text-table-value

distinguishedNameTableEntry OBJECT-CLASS
    SUBCLASS OF tableEntry                                          30
    MUST CONTAIN {distinguishedNameTableKey}
    ::= oc-distinguished-name-table-entry

distinguishedNameTableKey ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX
        distinguishedNameSyntax
    ::= at-distinguished-name-table-key



____________________Figure_1:__Representing_Tables_____________________



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1.  TextEntry, which define table entries with text keys, which may
    have single or multiple values of any type.  An attribute is
    defined to allow a text value, to support the frequent text key to
    text value mapping.  Additional values may be defined.

2.  DistinguishedNameEntry.  This is used for associating information
    with globally defined objects.  This approach should be used where
    the number of objects in the table is small or very sparsely
    spread over the DIT. In other cases where there are many objects
    or the objects are tightly clustered in the DIT, the subtree
    approach defined in Section 2 will be preferable.  No value
    attributes are defined for this type of entry.  An application of
    this will make appropriate subtyping to define the needed values.

This is best illustrated by example.  Consider the MTA:


CN=Bells, OU=Computer Science,
O=University College London, C=GB

Suppose that the MTA needs a table mapping from private keys to fully
qualified domain names (this example is fictitious).  The table might
be named as:

CN=domain-nicknames,
CN=Bells, OU=Computer Science,
O=University College London, C=GB


To represent a mapping in this table from ``euclid'' to
``bloomsbury.ac.uk'', the entry:

CN=euclid, CN=domain-nicknames,
CN=Bells, OU=Computer Science,
O=University College London, C=GB


will contain the attribute:

TextValue=bloomsbury.ac.uk


A second example, showing the use of DistinguishedNameEntry is now
given.  Consider again the MTA:

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_______________________________________________________________________
subtree OBJECT-CLASS
    SUBCLASS OF top
    MUST CONTAIN {commonName}
    MAY CONTAIN {manager}
    ::= oc-subtree

___________________Figure_2:__Representing_Subtrees____________________


CN=Bells, OU=Computer Science,
O=University College London, C=GB


Suppose that the MTA needs a table mapping from MTA Name to bilateral
agreement information of that MTA. The table might be named as:

CN=MTA Bilateral Agreements,
CN=Bells, OU=Computer Science,
O=University College London, C=GB


To represent information on the MTA:

CN=Q3T21, ADMD=Gold 400, C=GB


There would be an entry in this table with the Relative Distinguished
Name of the table entry being the Distinguished Name of the MTA being
referred to.  The MTA Bilateral information would be an attribute in
this entry.


2  Representing Subtrees

A subtree is similar to a table, except that the keys are constructed
a distinguished name hierarchy relative to the location of the subtree
in the DIT. The subtree effectively starts a private ``root'', and has
distinguished names relative to this root.  Typically, this approach
is used to associate local information with global objects.  The
schema used is defined in Figure 2.  Functionally, this is equivalent
to a table with distinguished name keys.  The table approach is best
when the tree is very sparse.  This approach is better for subtrees
which are more populated.


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INTERNET--DRAFT           Representing Subtrees          November 1992


The subtree object class defines the root for a subtree in an
analogous means to the table.  Information within the subtree will
generally be defined in the same way as for the global object, and so
no specific object classes for subtree entries are needed.
For example consider University College London.


O=University College London, C=GB

Suppose that the UCL needs a private subtree, with interesting
information about directory objects.  The table might be named as:


CN=private subtree,
O=University College London, C=GB

UCL specific information on Inria might be stored in the entry:


O=Inria, C=FR,
CN=private subtree,
O=University College London, C=GB

Practical examples of this mapping are given in [HK92].


References

[CCI88] The Directory --- overview of concepts, models and services,
        December 1988. CCITT X.500 Series Recommendations.

[HK92]  S.E. Hardcastle-Kille. MHS use of the directory to support
        MHS routing, April 1992. Internet Draft.


3  Security Considerations

Security considerations are not discussed in this INTERNET--DRAFT .


4  Author's Address


    Steve Hardcastle-Kille

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INTERNET--DRAFT           Representing Subtrees          November 1992


    ISODE Consortium
    PO Box 505
    London
    SW11 1DX
    England

    Phone:  +44-71-223-4062


    EMail:  S.Kille@ISODE.COM

    DN: CN=Steve Hardcastle-Kille,
    O=ISODE Consortium, C=GB


    UFN: S. Hardcastle-Kille, ISODE Consortium, GB





























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A  Object Identifier Assignment


_______________________________________________________________________
mhs-ds OBJECT-IDENTIFIER ::= {iso(1) org(3) dod(6) internet(1) private(4)
          enterprises(1) isode-consortium (453) mhs-ds (3)}

tables OBJECT IDENTIFIER ::= {mhs-ds 1}

oc OBJECT IDENTIFIER ::= {tables 1}
at OBJECT IDENTIFIER ::= {tables 2}

oc-subtree OBJECT IDENTIFIER ::= {oc 1}
oc-table OBJECT IDENTIFIER ::= {oc 2}                               10
oc-table-entry OBJECT IDENTIFIER ::= {oc 3}
oc-text-table-entry OBJECT IDENTIFIER ::= {oc 4}
oc-distinguished-name-table-entry  OBJECT IDENTIFIER ::= {oc 5}

at-text-table-key OBJECT IDENTIFIER ::= {at 1}
at-text-table-value OBJECT IDENTIFIER ::= {at 2}
at-distinguished-name-table-key OBJECT IDENTIFIER ::= {at 3}


_______________Figure_3:__Object_Identifier_Assignment_________________





















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