Schema for Representing CORBA Object References in an LDAP Directory
A schema for storing CORBA object references in an LDAP directory.
Ryan, V., Lee, R., and S. Seligman, "Schema for Representing CORBA Object References in an LDAP Directory", RFC 2714, DOI 10.17487/RFC2714, October 1999, <https://www.rfc-editor.org/info/rfc2714>.
@misc{rfc2714,
series = {Request for Comments},
number = 2714,
howpublished = {RFC 2714},
publisher = {RFC Editor},
doi = {10.17487/RFC2714},
url = {https://www.rfc-editor.org/info/rfc2714},
author = {V. Ryan and R. Lee and S. Seligman},
title = {{Schema for Representing CORBA Object References in an LDAP Directory}},
pagetotal = 10,
year = 1999,
month = oct,
} RFC text
Contents
Network Working Group V. Ryan
Request for Comments: 2714 R. Lee
Category: Informational S. Seligman
Sun Microsystems, Inc.
October 1999
Schema for Representing CORBA Object References in an LDAP Directory
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
Abstract
CORBA [CORBA] is the Common Object Request Broker Architecture
defined by the Object Management Group. This document defines the
schema for representing CORBA object references in an LDAP directory
[LDAPv3].
1. Introduction
This document assumes that the reader has a general understanding of
CORBA.
Traditionally, LDAP directories have been used to store data. Users
and programmers think of the directory as a hierarchy of directory
entries, each containing a set of attributes. You look up an entry
from the directory and extract the attribute(s) of interest. For
example, you can look up a person's telephone number from the
directory. Alternatively, you can search the directory for entries
with a particular set of attributes. For example, you can search for
all persons in the directory with the surname "Smith".
CORBA applications require access to CORBA objects. Traditionally,
CORBA applications have used the COS Naming service for storage and
retrieval of CORBA object references. When deployed in environments
with a directory, CORBA applications should be able to use the
directory as a repository for CORBA object references. The directory
provides a centrally administered, and possibly replicated, service
for use by CORBA applications distributed across the network.
For example, an application server may use the directory for
"registering" CORBA objects representing the services that it
manages, so that a client can later search the directory to locate
those services as it needs.
The motivation for this document is to define a common way for
applications to store and retrieve CORBA object references from the
directory. Using this common schema, any CORBA application that
needs to read or store CORBA object references in the directory can
do so in an interoperable way.
Note that this schema is defined for storing CORBA "object
references," not CORBA objects in general. There might be other ways
to store CORBA objects in an LDAP directory but they are not covered
by this schema.
2. Representation of CORBA Object References
This document defines schema elements to represent a CORBA object
reference in LDAP directory. Applications in possession of a
reference to an object can invoke calls on that object. Such a
reference is termed an "interoperable object reference," or IOR.
Access to CORBA objects by using IORs is achieved transparently to
the application, by means of the General Inter-ORB Protocol.
A CORBA object reference is represented in the directory by the
object class corbaObjectReference. corbaObjectReference is a subclass
of the abstract corbaObject object class. corbaObjectReference is an
auxiliary object class, which means that it needs to be mixed in with
a structural object class.
The object class corbaContainer is used in a directory entry which
represents a CORBA object or object reference. It is a structural
object class, and when representing an object reference, the
corbaObjectReference object class would also need to be present in
the entry. corbaContainer is not required when a subclass of
corbaObject (such as corbaObjectReference) is mixed in with another
structural object class.
The definitions for the object classes corbaObject,
corbaObjectReference, and corbaContainer are presented in Section 4.
The corbaObject class has two optional attributes: corbaRepositoryId
and description. corbaRepositoryId is a multivalued attribute that
is used to store the repository ids of the interfaces implemented by
a CORBA object. description is used to store a textual description
of a CORBA object.
The corbaObjectReference class has one mandatory attribute: corbaIor.
corbaIor is used to store the object's stringified IOR.
corbaIor and corbaRepositoryId are defined in Section 3; description
is defined in [v3Schema].
3. Attribute Type Definitions
The following attribute types are defined in this document:
corbaIor
corbaRepositoryId
3.1 corbaIor
This attribute stores the string representation of the interoperable
object reference (IOR) for a CORBA object. An IOR is an opaque handle
for the object which contains the information necessary to locate the
object, even if the object is in another ORB.
This attribute's syntax is 'IA5 String' and its case is
insignificant.
( 1.3.6.1.4.1.42.2.27.4.1.14
NAME 'corbaIor'
DESC 'Stringified interoperable object reference of a CORBA object'
EQUALITY caseIgnoreIA5Match
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
SINGLE-VALUE
)
3.2 corbaRepositoryId
Each CORBA interface has a unique "repository id" (also called "type
id") that identifies the interface. A CORBA object has one or more
repository ids, one for each interface that it implements.
The format of a repository id can be any string, but the OMG
specifies four standard formats:
a. IDL-style
IDL:Prefix/ModuleName/InterfaceName:VersionNumber
For example, the repository id for the "NamingContext" in OMG's COS
Naming module is: "IDL:omg.org/CosNaming/NamingContext:1.0".
b. RMI-style
RMI:ClassName:HashCode[:SUID]
This format is used by RMI-IIOP remote objects [RMI-IIOP].
"ClassName" is the fully qualified name of the class (for example,
"java.lang.String"). "HashCode" is the object's hash code (that is,
that obtained by invoking the "hashCode()" method). "SUID" is the
"stream unique identifier", which is a 64-bit number that uniquely
identifies the serialization version of the class; SUID is optional
in the repository id.
c. DCE-style
DCE:UUID
This format is used for DCE/CORBA interoperability [CORBA-DCE].
"UUID" represents a DCE UUID.
d. "local"
This format is defined by the local Object Request Broker (ORB).
The corbaRepositoryId attribute is a multivalued attribute; each
value records a single repository id of an interface implemented by
the CORBA object. This attribute need not contain a complete list of
the interfaces implemented by the CORBA object.
This attribute's syntax is 'Directory String' and its case is
significant. The values of this attribute are encoded using UTF-8.
Some values may require translation from their native representation
in order to be correctly encoded using UTF-8.
( 1.3.6.1.4.1.42.2.27.4.1.15
NAME 'corbaRepositoryId'
DESC 'Repository ids of interfaces implemented by a CORBA object'
EQUALITY caseExactMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
)
4. Object Class Definitions
The following object classes are defined in this document:
corbaContainer
corbaObject
corbaObjectReference
4.1 corbaContainer
This structural object class represents a container for a CORBA
object.
( 1.3.6.1.4.1.42.2.27.4.2.10
NAME 'corbaContainer'
DESC 'Container for a CORBA object'
SUP top
STRUCTURAL
MUST ( cn )
)
4.2 corbaObject
This abstract object class is the root class for representing a CORBA
object.
( 1.3.6.1.4.1.42.2.27.4.2.9
NAME 'corbaObject'
DESC 'CORBA object representation'
SUP top
ABSTRACT
MAY ( corbaRepositoryId $ description )
)
4.3 corbaObjectReference
This auxiliary object class represents a CORBA object reference. It
must be mixed in with a structural object class.
( 1.3.6.1.4.1.42.2.27.4.2.11
NAME 'corbaObjectReference'
DESC 'CORBA interoperable object reference'
SUP corbaObject
AUXILIARY
MUST ( corbaIor )
)
5. Security Considerations
Obtaining a reference to an object and storing it in the directory
may make a handle to the object available to a wider audience. This
may have security implications.
6. Acknowledgements
We would like to thank Sanjeev Krishnan of Sun Microsystems, Simon
Nash of IBM, and Jeffrey Spirn of Oracle for their comments and
suggestions.
7. References
[CORBA] The Object Management Group, "Common Object Request
Broker Architecture Specification 2.2",
http://www.omg.org
[CORBA-DCE] Distributed Systems Technology Center and Digital
Equipment Corporation, "DCE/CORBA Interworking
Specification", May 1998.
http://www.omg.org/library/schedule/
DCE_CORBA_Interworking_RFP.html
[LDAPv3] Wahl, M., Howes, T. and S. Kille, "Lightweight Directory
Access Protocol (v3)", RFC 2251, December 1997.
[RMI-IIOP] IBM and Java Software, Sun Microsystems, Inc., "RMI over
IIOP", June 1999. http://java.sun.com/products/rmi-
iiop/index.html
[v3Schema] Wahl, M., "A Summary of the X.500(96) User Schema for use
with LDAPv3", RFC 2256, December 1997.
8. Authors' Addresses
Vincent Ryan
Sun Microsystems, Inc.
Mail Stop EDUB03
901 San Antonio Road
Palo Alto, CA 94303
USA
Phone: +353 1 819 9151
EMail: vincent.ryan@ireland.sun.com
Rosanna Lee
Sun Microsystems, Inc.
Mail Stop UCUP02-206
901 San Antonio Road
Palo Alto, CA 94303
USA
Phone: +1 408 863 3221
EMail: rosanna.lee@eng.sun.com
Scott Seligman
Sun Microsystems, Inc.
Mail Stop UCUP02-209
901 San Antonio Road
Palo Alto, CA 94303
USA
Phone: +1 408 863 3222
EMail: scott.seligman@eng.sun.com
9. Appendix - LDAP Schema
-- Attribute types --
( 1.3.6.1.4.1.42.2.27.4.1.14
NAME 'corbaIor'
DESC 'Stringified interoperable object reference of a CORBA object'
EQUALITY caseIgnoreIA5Match
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
SINGLE-VALUE
)
( 1.3.6.1.4.1.42.2.27.4.1.15
NAME 'corbaRepositoryId'
DESC 'Repository ids of interfaces implemented by a CORBA object'
EQUALITY caseExactMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
)
-- from RFC-2256 --
( 2.5.4.13
NAME 'description'
EQUALITY caseIgnoreMatch
SUBSTR caseIgnoreSubstringsMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{1024}
)
-- Object classes --
( 1.3.6.1.4.1.42.2.27.4.2.9
NAME 'corbaObject'
DESC 'CORBA object representation'
SUP top
ABSTRACT
MAY ( corbaRepositoryId $ description )
)
( 1.3.6.1.4.1.42.2.27.4.2.10
NAME 'corbaContainer'
DESC 'Container for a CORBA object'
SUP top
STRUCTURAL
MUST ( cn )
)
( 1.3.6.1.4.1.42.2.27.4.2.11
NAME 'corbaObjectReference'
DESC 'CORBA interoperable object reference'
SUP corbaObject
AUXILIARY
MUST ( corbaIor )
)
-- Matching rule from ISO X.520 --
( 2.5.13.5
NAME 'caseExactMatch'
SYNTAX 1.3.6.1.4.1.1466.115.121.1.15
)
10. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
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or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
AI ELI5
On this page
§1Introduction
CORBA (Common Object Request Broker Architecture) is a middleware system that lets programs on different computers call methods on each other's objects. Traditionally, CORBA applications use the COS Naming service to register and discover objects. However, many organizations have deployed LDAP directories as a centralized, replicated naming and directory service. This RFC defines a schema so CORBA applications can store CORBA object references in LDAP directories instead of (or alongside) the COS Naming service.
Like RFC 2713 (Java objects in LDAP), this document provides a common interoperable way to store and retrieve CORBA objects from LDAP. A CORBA application server might register the services it manages in the LDAP directory, so client applications can search for and locate those services by name and properties.
CORBA programs are on different computers and call each other. They used to find each other using a special naming service. Now they can use a regular directory instead, just like looking someone up in a phone book.
§2CORBA Object References and IORs
A CORBA object reference (or IOR, "Interoperable Object Reference") is an opaque handle that a CORBA client can use to invoke methods on a remote object. The IOR contains enough information for the CORBA runtime to locate and communicate with the object across the network, even if it is running in a different CORBA implementation. The stringified form of an IOR (a text representation) is what gets stored in the directory.
In addition to the IOR, objects have repository IDs (also called "type IDs"), which are unique identifiers for the interfaces the object implements. The RFC defines four standard formats for repository IDs: IDL-style (for CORBA IDL objects), RMI-style (for Java RMI-IIOP remote objects), DCE-style (for DCE/CORBA interoperability), and local (ORB-specific). A single CORBA object may implement multiple interfaces, each with its own repository ID.
A CORBA object reference is like a phone number: it tells you how to reach an object. The interface is like a business card that says what services the object provides.
§3Object Classes and Attributes
The schema defines three object classes. corbaObject is an abstract base class with two optional attributes: corbaRepositoryId (stores the IDs of all interfaces the object implements) and description (human-readable text). corbaContainer is a structural class used as a dedicated container for a CORBA object entry; it has a mandatory common name (cn). corbaObjectReference is an auxiliary class that adds one mandatory attribute, corbaIor, which stores the stringified interoperable object reference.
To create a directory entry for a CORBA object reference, use javaContainer mixed with corbaObjectReference, or use corbaContainer directly. The corbaIor attribute must contain the stringified form of the IOR, and corbaRepositoryId may contain one or more repository IDs identifying the interfaces.
The schema has three building blocks. corbaObject is the base. corbaContainer is a container to hold the object. corbaObjectReference is the special part that stores the reference and interfaces.
§4Using CORBA References in LDAP
When a CORBA application wants to register a service, it creates a stringified IOR from its CORBA object, then creates an LDAP entry with the corbaObjectReference class. The entry includes the corbaIor attribute (the stringified reference) and optionally the corbaRepositoryId attribute(s) listing the interfaces. Clients search the directory by name or other attributes to find the service they need.
Because the corbaIor attribute's syntax is IA5 String with case-insensitive matching, the stringified reference is human-readable and searchable. The schema's use of standard LDAP conventions makes CORBA object references compatible with any LDAP directory, and the interoperable object reference format means the reference works across different ORB implementations.
To register an object, you write down its phone number (the IOR) and what it does (its interfaces) in the directory. To find an object, you search the directory for the service you want, get the phone number, and call it.
§5Security and Interoperability
Storing a CORBA object reference in the directory makes the reference available to anyone with directory access, potentially exposing the object to a wider audience than intended. Applications deploying this schema should be aware that storing an IOR in the directory may broaden the set of potential callers. Access control mechanisms in the LDAP server provide the primary way to restrict who can see registered objects.
The schema is fully interoperable because it relies only on standard LDAP attribute types and conventions. Both Java RMI-IIOP (which uses RMI-style repository IDs) and pure CORBA applications (using IDL-style repository IDs) can coexist in the same directory. This schema was developed in parallel with RFC 2713 (Java objects in LDAP) at Sun Microsystems, and the two schemas are complementary.
Be aware that registering an object in a directory makes it visible to everyone who can read the directory. Use access controls to keep private objects private. The nice thing is that CORBA programs and Java programs can both use the same directory.