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Network Working Group                                           S. KilleRequest for Comments: 1837                              ISODE ConsortiumCategory: Experimental                                       August 1995Representing Tables and Subtrees in the X.500 DirectoryStatus 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.Kille                         Experimental                      [Page 1]

RFC 1837                 Representing Subtrees               August 1995   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:-----------------------------------------------------------------------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 ::= {Kille                         Experimental                      [Page 2]

RFC 1837                 Representing Subtrees               August 1995    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 Tables1.  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 inSection 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=GBSuppose that the MTA needs a table mapping from private keys to fullyqualified domain names (this example is fictitious).  The table mightbe named as:CN=domain-nicknames,CN=Bells, OU=Computer Science,O=University College London, C=GBKille                         Experimental                      [Page 3]

RFC 1837                 Representing Subtrees               August 1995To 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=GBwill contain the attribute:TextTableValue=bloomsbury.ac.ukA second example, showing the use of DistinguishedNameEntry is nowgiven.  Consider again the MTA:CN=Bells, OU=Computer Science,O=University College London, C=GBSuppose that the MTA needs a table mapping from MTA Name to bilateralagreement information of that MTA. The table might be named as:CN=MTA Bilateral Agreements,CN=Bells, OU=Computer Science,O=University College London, C=GBTo 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:   DistinguishedNameTableValue=<CN=Q3T21, ADMD=Gold 400, C=GB>,   CN=MTA Bilateral Agreements,   CN=Bells, OU=Computer Science,   O=University College London, C=GBKille                         Experimental                      [Page 4]

RFC 1837                 Representing Subtrees               August 19952.  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].Kille                         Experimental                      [Page 5]

RFC 1837                 Representing Subtrees               August 19953.  Acknowledgements   Acknowledgements 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., "MHS use of the X.500 Directory to Support MHS       Routing",RFC 1801, ISODE Consortium, June 1995.4.  Security Considerations   Security issues are not discussed in this memo.5.  Author's Address   Steve Kille   ISODE Consortium   The Dome   The Square   Richmond   TW9 1DT   England   Phone:  +44-81-332-9091   Internet EMail:  S.Kille@ISODE.COM   X.400:  I=S; S=Kille; O=ISODE Consortium; P=ISODE;   A=Mailnet; C=FI;   DN: CN=Steve Kille,   O=ISODE Consortium, C=GB   UFN: S. Kille, ISODE Consortium, GBKille                         Experimental                      [Page 6]

RFC 1837                 Representing Subtrees               August 1995A.  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}                               10oc-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 AssignmentKille                         Experimental                      [Page 7]