RFC 1837

Network Working Group
Request for Comments: 1837
Category: Experimental

S. Kille
ISODE Consortium
August 1995

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Representing Tables and Subtrees in the X.500 Directory

Status of this Memo

This memo defines an Experimental Protocol for the Internet community. This memo does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.

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.

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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:

The object does not have a directory entry
There is no authority to place the parameters in the global entry
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:

-----------------------------------------------------------------------
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 ::= {

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    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: