RFC2293 - Representing Tables and Subtrees in the X.500 Directory

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　　Network Working Group S. Kille
Request for Comments: 2293 Isode Ltd.
Obsoletes: 1837 March 1998
Category: Standards Track

Representing Tables and Subtrees in the X.500 Directory

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1998). All Rights Reserved.

Abstract

This document defines techniques for representing two types of
information mapping in the OSI Directory [1].

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.

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

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 optimization, 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 organization, it will be located under the organization.

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:

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

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

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

textTableKey ATTRIBUTE ::= {
SUBTYPE OF name 20
WITH SYNTAX DirectoryString {ub-name}
ID at-text-table-key}

textTableValue ATTRIBUTE ::= {
SUBTYPE OF name
WITH SYNTAX DirectoryString {ub-description}
ID at-text-table-value}

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

distinguishedNameTableKey ATTRIBUTE ::= {
SUBTYPE OF distinguishedName
ID at-distinguished-name-table-key}

Figure 1: Representing Tables

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:

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

will contain the attribute:

TextTableValue=bloomsbury.ac.uk

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

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 which has the Distinguished Name:

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. Using a non-standard notation, the Distinguished Name of
the table entry is:

DistinguishedNameTableKey=<CN=Q3T21, ADMD=Gold 400, C=GB>,
CN=MTA Bilateral Agreements,
CN=Bells, OU=Computer Science,
O=University College London, C=GB

2 Representing Subtrees

A subtree is similar to a table, except that the keys are constructed
as 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.

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

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

Figure 2: Representing Subtrees

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 [2].

3 Acknowledgments

Acknowledgments for work on this document are given in [2].

References

[1] The Directory --- overview of concepts, models and services,
1993. CCITT X.500 Series Recommendations.

[2] Kille, S.E., "X.400-MHS use of the X.500 directory to support
X.400-MHS routing," RFC1801, June 1995.

4 Security Considerations

Security considerations are not discussed in this memo.

5 Author's Address

Steve Kille
Isode Ltd
The Dome
The Square
Richmond
TW9 1DT
England

Phone: +44-181-332-9091
EMail: S.Kille@ISODE.COM

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 (7)}

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

Full Copyright Statement

Copyright (C) The Internet Society (1998). All Rights Reserved.

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