path: root/doc/rfc/rfc1276.txt

Network Working Group                            S.E. Hardcastle-Kille
Requests for Comments 1276                   University College London
                                                         November 1991






          Replication and Distributed Operations extensions
             to provide an Internet Directory using X.500







Status of this Memo
    This RFC specifies an IAB standards track protocol for the
    Internet community, and requests discussion and suggestions for
    improvements.  Please refer to the current edition of the ``IAB
    Official Protocol Standards'' for the standardization state and
    status of this protocol.  Distribution of this memo is unlimited.

Abstract
    Some requirements on extensions to X.500 are described in the
    RFC[HK91b], in order to build an Internet Directory using
    X.500(1988).  This document specifies a set of solutions to the
    problems raised.  These solutions are based on some work done for
    the QUIPU implementation, and demonstrated to be effective in a
    number of directory pilots.  By documenting a de facto standard,
    rapid progress can be made towards a full-scale pilot.  These
    procedures are an INTERIM approach.  There are known
    deficiencies, both in terms of manageability and scalability.
    Transition to standard approaches are planned when appropriate
    standards are available.  This RFCwill be obsoleted at this
    point.
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RFC 1276         Internet Directory Replication          November 1991


Contents

1   Approach                                                         2

2   Extensions to Distributed Operations                             3


3   Alternative DSAs                                                 4

4   Data Model                                                       5


5   DSA Naming                                                       6

6   Knowledge Representation                                         6

7   Replication Protocol                                             9


8   New Application Context                                         12

9   Policy on Replication Procedures                                12


10  Use of the Directory by Applications                            12

11  Migration and Scaling                                           12

12  Security Considerations                                         13


13  Author's Address                                                13

A   ASN.1 Summary and Object Identifier Allocation                  14


List of Figures

    1      Knowledge Attributes  .   .   .   .   .   .   .   .       8

    2      Replication Protocol  .   .   .   .   .   .   .   .      10
    3      Summary of the ASN.1  .   .   .   .   .   .   .   .      17



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1  Approach

There are a number of non-negotiable requirements which must be met
before a directory can be deployed on the Internet [HK91b].  These
problems are being tackled in the standards arena, but there is
currently no stable solution.  One approach would be to attempt to
intercept the standard.  Difficulties with this would be:


 o  Defining a coherent intercept would be awkward, and the effort
    would probably be better devoted to working on the standard.  It
    is not even clear that such an intercept could be defined.

 o  The target is moving, and it is always tempting to track it, thus
    causing more delay.

 o  There would be a delay involved with this approach.  It would be
    too late to be useful for a rapid start, and sufficiently close to
    the timing of the final standard that many would choose not to
    implement it.

Therefore, we choose to take a simple approach.  This is a good deal
simpler than the full X.500 approach, and is based on operational
experience.  The advantages of this approach are:


 o  It is proven in operation.  This RFCis simply documenting what is
    being done already.

 o  There will be a minimum of delay in starting to use the approach.

 o  The approach is simpler, and so the cost of implementation is much
    less.  It will therefore be much more attractive to add into an
    implementation, as it is less effort, and can be further ahead of
    the standard.

These procedures are an INTERIM approach.  There are known
deficiencies, both in terms of manageability and scalability.
Transition to standard approaches are planned when appropriate
standards are available.  This RFCwill be obsoleted at this point.





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2  Extensions to Distributed Operations

The distributed operations of X.500 assume that all DUAs and DSAs are
fully interconnected with a global network service.  For the Internet
Pilot, this assumption is invalid.  DSAs may be operated over TCP/IP,
TP4/CLNS, or TP0/CONS.
The extension to distributed operations to support this situation is
straightforward.  We define the term community as an environment where
direct (network) communication is possible.  Communities may be
separated because they operate different protocols, or because of lack
of physical connectivity.  Example communities are the DARPA/NSF
Internet, and the Janet private X.25 network.  A network entity in a
community is addressed by its Network Address.  If two network
entities are in the same community, they can by definition
communicate.  A community is identified by a set of network address
prefixes.  For the approach to be useful, this set should be small
(typically 1).  For TCP/IP Networks, and X.25 Networks not providing
CONS, the approach is described in [HK91a] allows for communities to
be defined for the networks of operational interest.

This model can be used to determine whether a pair of application
entities can communicate.  For each entity, determine the presentation
address (typically by directory lookup).  Each network address in the
presentation address will have a single associated community.  The set
of communities to which each application entity belongs can thus be
determined.  If the two application entities have a common community,
then they can communicate directly.
Two extensions to the standard distributed operations are needed.


1.  Consider a DSA (the local DSA) which is contacted by either a DUA
    or DSA (the calling entity) to resolve a query.  The local DSA
    determines that the query must be progressed by another DSA (the
    referred-to DSA). The DSA will make a chain/referral choice.  If
    chaining is prohibited by service control, a referral will be
    passed back.  Otherwise, if the local DSA prefers to chain (e.g.,
    for policy reasons) it will then chain.  The remaining situation
    is that the local DSA prefers to give a referral.  It shall only
    do so if it believes that the calling entity can directly connect
    to the referred-to DSA. If the calling entity is a DUA, it should
    be assumed to belong only to the community of the called network
    address.  If the calling entity is a DSA, its communities should
    be determined by lookup of the DSA's presentation address in the
    directory.  The communities of the referred-to DSA can be

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    determined from its presentation address, which will either be
    present in the reference or can be looked up in the directory.  If
    the calling entity and the referred-to DSA do not have a common
    community, then chaining shall be used.  Otherwise, a referral may
    be passed back to the calling entity.

2.  Consider that a DSA (or DUA), termed here the local entity is
    following a referral (to a referred-to DSA). In some cases, the
    local entity and referred-to DSA will not be able to communicate
    directly (i.e., not have a common community).  There are two
    approaches to solve this:

   (a)  Pass the query to a DSA it would use to resolve a query for
        the entry one level higher in the DIT. This will work,
        provided that this DSA follows this specification.  This
        default mechanism will work without additional configuration.

   (b)  Use a ``relay DSA'' to access the community.  A relay DSA is
        one which can chain the query on to the remote community.  The
        relay DSA must belong to both the remote community and to at
        least one community to which the local entity belongs.  The
        choice of relay DSA for a given community will be manually
        configured by a DSA manager to enable access to a community to
        which there is not direct connectivity.  Typically this will
        be used where the default DSA is a poor choice (e.g., because
        relaying is not authorised through this DSA).

    A DSA conforming to this specification shall follow these
    procedures.  A DUA may also follow these procedures, and this will
    give improvements in some circumstances (i.e., the ability to
    resolve certain queries without use of chaining).  However, this
    specification does not place requirements on DUAs.


3  Alternative DSAs

There is a need to give information on slave copies of data.  This can
be done using the standard protocol, but modifying the semantics.
This relies on the fact that there may only be a single subordinate
reference or cross reference.

If there is a need to include references to master and slave data (EDB
copies) in a referral, then this should be done in a referral by
specifying a subordinate reference with multiple values.  This cannot

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be a standard subordinate reference, which would only have a single
value.  Therefore, this usage does not conflict with standard
references.  The first reference is the master copy, and subsequent
references are slave copies.


4  Data Model

The X.500 data model takes the unit of mastering data as the entry.  A
DSA may hold an arbitrary collection of entries.  We restrict this
model so that for the replication protocol defined in this
specification the base unit of replication (shadowing) is the complete
set of immediate subordinate entries of a given entry, termed an Entry
Data Block (EDB). An EDB is named by its parent entry.  It contains
the relative distinguished names of all of the children of the entry,
and each of the child entries.  For each entry, this comprises all
attributes of the entry, the relative distinguished name, and
knowledge information associated with the entry.  If a DSA holds
(non-cached) information on an entry, it will hold information on all
of its siblings.  One DSA will hold a master EDB. This will contain
two types of entry:

1.  Entries for which this DSA is the master.

2.  Slave copies of entries which are mastered in another DSA,
    indicated by a subordinate reference.  This copy must be
    maintained automatically by the DSA holding the master EDB.


Thus the master EDB contains a mixture of master entries, and entries
which are mastered elsewhere and shadowed by the DSA holding the
master EDB on an entry by entry basis.  Other DSAs may hold slave
copies of this EDB (slave EDBs), which are replicated in their
entirity directly or indirectly from the master EDB. This approach has
the following advantages.

 o  Name resolution is simplified, and performance improved.

 o  Single level searching and listing have good performance, and are
    straightforward to implement.  In a more general case of applying
    the standard, without sophisticated replication, these operations
    might require to access very many DSAs and be prohibitively
    expensive.


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5  DSA Naming

All DSAs must be named in the DIT, and the master definition of the
presentation address stored in this entry.  X.500 (including some of
the extension work) implies that the presentation address information
is extensively replicated (manually).  The management overhead implied
by this is not acceptable.
Care must be taken to prevent deadlock in determining a DSAs address.
This is solved by:


1.  Use of a well known DSA with ``root knowledge''

2.  Naming DSAs in a manner which prevents deadlocks.  Currently this
    is done by giving DSAs names high in the DIT.

The Internet Pilot will need to define detailed policies for naming
DSAs, in conjunction with the replication policy.  This will be
defined in a future RFC.


6  Knowledge Representation


Knowledge information is represented in the DIT. It seems unreasonable
to manage this by any other means.  Knowledge information is
represented in an entry by use of knowledge attributes.  These
attributes are considered separately from all the other attributes in
the entry which are termed ``user attributes''.  Each entry in a
master EDB will be in one of four categories.

1.  The entry is a leaf entry mastered in this EDB, and so only
    contains user attributes

2.  The level below has an associated EDB (i.e., the DIT continues
    downwards to use the data model of this specification).  All
    attributes of this entry will be mastered in this entry.  The
    entry will contain an attribute with the name of the DSA which
    holds the master of the associated EDB. Optionally, it will
    contain an attribute holding the names of DSAs which hold slave
    EDBs.  The entry may not hold a subordinate reference attribute.
    The DIT is followed by use of the master and slave attributes.



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3.  The entry is mastered in a DSA which does not follow this
    specification.  The entry in the EDB will contain a master
    attribute, which holds a subordinate reference (or cross
    reference) to the DSA which holds the master entry.  The user
    attributes of the entry will be mastered in the DSA pointed to by
    the reference.  The DSA holding the master EDB, which actually
    acts as an intermediate shadow for this entry, will read these
    attributes from the DSA indicated by the reference, so that it
    will have a full copy of the entry, using a standared DSP Read
    operation.  This technique is called ``spot shadowing''.  Any
    access control on the entry being spot shadowed must be configured
    so that all attributes can be copied by the DSA holding the master
    EDB. DSAs taking slave copies of the EDB will not do spot
    shadowing.  However, the knowledge attributes will be copied, and
    may be used by this DSA (e.g., for modify operations).

4.  The entries at the level below are held in DSAs which do not
    follow this specification, and all of these are indicated by a set
    of NSSRs (Non Specific Subordinate Reference).  The NSSRs are
    stored as an attribute of the entry.  The user attributes are
    either mastered in the EDB.
    It is important to note that NSSRs are stored at the level above
    subordinate references.  At a given point in the DIT, if there are
    subordinate references, these are stored in shadow entries below
    that point, and named by the RDN. If there are NSSRs, they are
    stored in the entry itself, as there is no RDN associated with an
    NSSR. This approach is cleanest where there are either NSSRs or
    subordinate references, but not both.  For example, consider an
    Organisation HP, whose many OUs are stored in a set of DSAs
    indicated by by NSSRs.  Here, the NSSR attributes will be used to
    identify these DSAs.
    This model of replication is not tightly integrated with NSSRs.
    Where there is a mixture of NSSRs and Subordinate references at a
    given point in the DIT, this is handled by giving a single
    subordinate reference to a DSA which follows standard X.500
    distributed operations and can cleanly handle this mixture.  In
    practice, this is equivalent to not allowing a mixture of
    subordinate references and NSSRs.

The information framework needed to support this is defined in
Figure_1.______________________________________________________________




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InternetDSNonLeafObject ::= OBJECT-CLASS
        SUBCLASS OF top
        MUST CONTAIN {masterDSA}
        MAY CONTAIN {slaveDSA}

ExternalDSObject ::= OBJECT-CLASS
        SUBCLASS OF top
        MAY CONTAIN {SubordinateReference, CrossReference,          10
                NonSpecificSubordinateReference}
                        -- will contain exactly one of these references

MasterDSA ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX distinguishedNameSyntax
    SINGLE VALUE

SlaveDSA ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX distinguishedNameSyntax
                                                                    20
SubordinateReference ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX AccessPoint
    SINGLE VALUE

CrossReference ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX AccessPoint
    SINGLE VALUE

NonSpecificSubordinateReference ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX AccessPoint                               30

AccessPoint ::= SET {
        ae-title [0] Name,
        address  [2] PresentationAddress OPTIONAL }

                -- Same definition as X.500 AccessPoint,
                -- but presentation address is optional


___________________Figure_1:__Knowledge_Attributes_____________________

Two object classes are defined to support this approach:




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InternetDSNonLeafObject This is for where the level below follows the
    model defined here, and there is an Entry Data Block (EDB)
    containing the sibling entries.  The Entry itself contains master
    data.  The associated attributes are:

    MasterDSA The name of the DSA where the master EDB is held.

    SlaveDSA The names of DSAs which hold slave copies of the EDB for
        public access.

ExternalDSObject This is for where the entry and levels below are
    mastered according to X.500.  There are attributes corresponding
    to the standard knowledge references, which are used to resolve
    queries.  The presentation address is optional in these
    attributes.  If not present, it should be looked up in the DSAs
    own entry.  For NonSpecificSubordinateReference, the master of the
    entry will be in the master EDB, For SubordinateReference or
    CrossReference1 the DSA which masters the EDB will ``spot shadow''
    the entry, by reading it at intervals.  This will ensure that the
    master EDB contains a copy of each entry.  Single level searching
    can then be done efficiently where it is not required to access
    the master copy of the data.  DSAs holding slave copies of the EDB
    do not perform spot shadowing, but do receive copies of the
    references.


7  Replication Protocol
_______________________________________________________________________
GetEntryDataBlock ABSTRACT-OPERATION
        ARGUMENT GetEntryDataBlockArgument
        RESULT GetEntryDataBlockResult
        ERRORS {nameError,ServiceError,SecurityError,EDBVersionError}

EDBVersionError ABSTRACT-ERROR
        PARAMETER versionHeld EDBVersion


GetEntryDataBlockArgument ::= SET {                                 10

----------------------------
    1. These references are really the same.  The function and value
are the same.  The name depends on where the reference is stored.  It
may be preferable to have only one attribute.


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        entry [0] DistinguishedName,
        CHOICE {
                sendIfMoreRecentThan [1] EDBVersion,
                getVersionNumber [2] NULL,
                getEDB [3] NULL,        -- force retrieval
                continuation [4] SEQUENCE {
                        EDBVersion,
                        nextEntryPosition INTEGER }
                },
        maxEntries [5] INTEGER OPTIONAL                             20
                        -- if omitted return whole EDB in
                        -- one operation
}

GetEntryDataBlockResult ::= SEQUENCE {
                versionHeld [0] EDBVersion,
                [1] SEQUENCE OF RelativeEntry OPTIONAL,
                        -- if omitted, only version is returned
                nextEntryPostion INTEGER OPTIONAL
                        -- if omitted there are no more entries     30
        }



RelativeEntry ::= SEQUENCE {
        RelativeDistinguishedName,
        SET OF Attribute
        }

EDBVersion ::= UTCTime                                              40

___________________Figure_2:__Replication_Protocol_____________________

A ROS operation to support replication is defined in Figure 2.  This
pulls an entire copy of the EDB. In normal use, the initiator
specifies the EDB Version held.  If the responder has a more recent
version, then all of the entries in the EDB are returned.  There are
options to rerequest only the version of EDB held, or to return the
full EDB irrespective of the version held by the initiator.
For large EDBs, transfer of an entire EDB in a single operation would
lead to very large ROS PDUs.  This gives a definite scaling
limitation.  To overcome this, the protocol allows an EDB to be
retrived in chunks of a size (in number of entries) specified by the


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initiator.  The responder specifies a number which indicates the next
entry to be transferred.  The same operation can be used to retrieve
the next chunk of the EDB, with EDBVersion and the same integer as
parameters.
This approach is simple to implement.  It is less efficient than an
incremental technique.  When scaling dictates that an incremental
technique must be used, it is expected that a suitable standard will
be available.
An implementation issue that must be noted is how to deal with updates
whilst a multi-operation transfer is in progress.  There are two
possible approaches:


1.  Refuse/block updates until the EDB is transferred.  This may cause
    problems where the rate of update and transfer is high, as this
    may make update very difficult (for the manager).

2.  Create a new version of the EDB, whilst retaining the old EDB to
    complete the bulk transfer.  A suitable retentions strategy would
    be to hold an EDB version as long as the association on which it
    is being pulled it remains active.

3.  Allow the update and fail subsequent transfer requests for the
    EDB. This may cause both transfer failure and excessive waste of
    bandwidth due to retries if the rate of update and transfer is
    high.

If option 1.  or 3.  is chosen, for a widely replicated EDB where the
update rate is greater than a few changes per day, it is recommended
to configure the master EDB in a DSA which only replicates to one
other DSA. This second DSA can then control its update rate, and
safely perform a large fanout of replications (option 3).  The first
DSA will have reasonable availability for modifications (option 1).

This protocol will be used by DSAs to obtain copies of EDBs high in
the tree (typically root and national EDBs).  DSAs which need these
copies should establish bilateral agreements to access them2.
This protocol should only transfer user attributes.  In particular,
implementation specific attributes such as those needed to support

----------------------------
    2. QUIPU defines some attributes to register such agreements, but
these are probably not appropriate for this specification.


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private access control should not be transferred.  There may be
bilateral agreements on access control policy of the information
(e.g., size limits on listing), which are implemented by (different)
system specific techniques.


8  New Application Context

A DSA which follows these procedures will support a new
ApplicationContext ``Internet DSP'' defined in Appendix A. This will
be stored in the DSAs entry, so that support of the extensions defined
here can easily be determined.


9  Policy on Replication Procedures

To be effective, a directory configuration must be laid out.  These
protocols will need to be used in the framework of a pilot, and
service providers making available data for replication.
There is a requirement to manage the replication process.  This can be
done by a combination of local configuration (to register shadowing
agreements) and directory operations to set pointers to master and
slave copies of the data.


10  Use of the Directory by Applications


Care must be taken by users of the directory when replication is
available.  This is not a change from current use of X.500, but is
noted here as it is important.  Normal read requests should allow use
of copy information.  If the user of the directory believes that
information may be out of date (e.g., because an association could not
be established), then the request should be repeated and use of copy
data prohibited by service controls.


11  Migration and Scaling

The major scaling limit of this approach is the non-incremental
update.  This will put a limit on the maximum DIT fanout which can be
supported.  Given an average entry size of around a thousand bytes,
and a maximum reasonable transfer size is tens of megabytes, then the


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fanout limit of this approach is of order 10 000.  Note that smaller
organisations will tend to be registered geographically (e.g., in the
US, by State), so that the limit of the number of Organisations is
somewhat larger.  It should be noted that although the replication
technique described here is general, it is only intended for high
levels of the DIT. These figures assume this.
These techniques do not preclude use of other techniques for
replication.  It would be quite reasonable to replicate data using
this approach, and that which will be defined in X.500(92).


References

[HK91a] S.E. Hardcastle-Kille. Encoding network addresses to support
        operation over non-osi lower layers. Request for Comments
        RFC 1277, Department of Computer Science, University College
        London, November 1991.

[HK91b] S.E. Hardcastle-Kille. Replication requirement to provide an
        internet directory using X.500. Request for Comments
        RFC 1275, Department of Computer Science, University College
        London, November 1991.


12  Security Considerations

Security considerations are not discussed in this memo.


13  Author's Address

    Steve Hardcastle-Kille
    Department of Computer Science
    University College London
    Gower Street
    WC1E 6BT
    England


    Phone:  +44-71-380-7294

    EMail:  S.Kille@CS.UCL.AC.UK



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A  ASN.1 Summary and Object Identifier Allocation

There_are_a_few_object_identifiers_needed.__These_are_defined_here.____

InternetDSP  TAGS ::=
BEGIN

IMPORTS
    APPLICATION-SERVICE-ELEMENT, PORT, APPLICATION-CONTEXT,
    aCSE, ABSTRACT OPERATION
        FROM Remote-Operations-Notation-extension {joint-iso-ccitt
        remote-operations(4) notation-extension(2)}

                                                                    10
   id-as-mrse, id-as-mase, id-as-ms
        FROM MTSAccessProtocol {joint-iso-ccitt mhs-motis(6)
        protocols(0) modules(0) object-identifiers(0)}

   chainedReadASE, chainedSearchASE, chainedModifyASE
        FROM DirectorySystemProtocol {joint-iso-ccitt ds(5)
                modules(1) dsp(12)}

   DistinguishedName, RelativeDistinguishedName, Attribute
        FROM InformationFramework {joint-iso-ccitt ds(5)            20
                modules(1) InformationFramework(1)}


   ATTRIBUTE, OBJECT-CLASS
        FROM InformationFramework {joint-iso-ccitt ds(5)
        modules(1) informationFramework(1)};



internet-dsp OBJECT IDENTIFIER ::= {ccitt data(9) pss(2342)         30
        ucl(19200300) internet-dsp(107)}

-- General

at OBJECT IDENTIFIER ::= {internet-dsp at(1)}
oc OBJECT IDENTIFIER ::= {internet-dsp oc(2)}


-- Object Classes needed for association


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                                                                    40
id-ac-idsp  OBJECT IDENTIFIER ::= {internet-dsp ac-idsp(3))}
id-as-idsp  OBJECT IDENTIFIER ::= {internet-dsp as-idsp(4))}
id-ase-replication  OBJECT IDENTIFIER ::= {internet-dsp ase-replication(5))}


-- Attribute Types

master-dsa MasterDSA ::= {at 1}
slave-dsa SlaveDSA ::= {at 2}
subordinate-reference SubordinateReference ::= {at 3}               50
cross-reference CrossReference ::= {at 4}
nssr NonSpecificSubordinateReference ::= {at 5}

-- Object Classes

internet-ds-non-leaf-object InternetDSNonLeafObject ::= {oc 1}
external-ds-object ExternalDSObject ::= {oc 2}


-- Operation and Error bindings                                     60

getEntryDataBlock GetEntryDataBlock ::= 10

eDBVersionError EDBVersionError ::= 10


-- Protocol Definitions

replicationASE APPLICATION-SERVICE-ELEMENT
    OPERATIONS {getEntryDataBlock}                                  70
    ::= id-ase-replication

internet-dsp APPLICATION-CONTEXT
    APPLICATION SERVICE ELEMENTS {aCSE}
    BIND MSBind
    UNBIND MSUnbind
    REMOTE OPERATIONS {rOSE}
    OPERATIONS OF { chainedReadADSm chainedSearchASE,
        chainedModifyASE, replicationASE }
    ABSTRACT SYNTAXES {                                             80
        id-as-acse,
        id-as-idsp }
    ::= id-ac-idsp

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                                                                    90
InternetDSNonLeafObject ::= OBJECT-CLASS
        SUBCLASS OF top
        MUST CONTAIN {masterDSA}
        MAY CONTAIN {slaveDSA}

ExternalDSObject ::= OBJECT-CLASS
        SUBCLASS OF top
        MAY CONTAIN {SubordinateReference, CrossReference,
                NonSpecificSubordinateReference}
                        -- will contain exactly one of these references100

MasterDSA ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX distinguishedNameSyntax
    SINGLE VALUE

SlaveDSA ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX distinguishedNameSyntax

SubordinateReference ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX AccessPoint                              110
    SINGLE VALUE

CrossReference ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX AccessPoint
    SINGLE VALUE

NonSpecificSubordinateReference ::= ATTRIBUTE
    WITH ATTRIBUTE-SYNTAX AccessPoint

AccessPoint ::= SET {                                              120
        ae-title [0] Name,
        address  [2] PresentationAddress OPTIONAL }

                -- Same definition as X.500 AccessPoint,
                -- but presentation address is optional

GetEntryDataBlock ABSTRACT-OPERATION

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        ARGUMENT GetEntryDataBlockArgument
        RESULT GetEntryDataBlockResult
        ERRORS {nameError,ServiceError,SecurityError,EDBVersionError}130

EDBVersionError ABSTRACT-ERROR
        PARAMETER versionHeld EDBVersion


GetEntryDataBlockArgument ::= SET {
        entry [0] DistinguishedName,
        CHOICE {
                sendIfMoreRecentThan [1] EDBVersion,
                getVersionNumber [2] NULL,                         140
                getEDB [3] NULL,        -- force retrieval
                continuation [4] SEQUENCE {
                        EDBVersion,
                        nextEntryPosition INTEGER }
                },
        maxEntries [5] INTEGER OPTIONAL
                        -- if omitted return whole EDB in
                        -- one operation
}
                                                                   150
GetEntryDataBlockResult ::= SEQUENCE {
                versionHeld [0] EDBVersion,
                [1] SEQUENCE OF RelativeEntry OPTIONAL,
                        -- if omitted, only version is returned
                nextEntryPostion INTEGER OPTIONAL
                        -- if omitted there are no more entries
        }


                                                                   160
RelativeEntry ::= SEQUENCE {
        RelativeDistinguishedName,
        SET OF Attribute
        }

EDBVersion ::= UTCTime
END

___________________Figure_3:__Summary_of_the_ASN.1_____________________



Hardcastle-Kille                                               Page 17