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Network Working Group M. Smith Request for Comments: 2079 Netscape Communications Category: Standards Track January 1997

 Definition of an X.500 Attribute Type and an Object Class to Hold
                Uniform Resource Identifiers (URIs)

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.


 Uniform Resource Locators (URLs) are being widely used to specify the
 location of Internet resources.  There is an urgent need to be able
 to include URLs in directories that conform to the LDAP and X.500
 information models, and a desire to include other types of Uniform
 Resource Identifiers (URIs) as they are defined.  A number of
 independent groups are already experimenting with the inclusion of
 URLs in LDAP and X.500 directories.  This document builds on the
 experimentation to date and defines a new attribute type and an
 auxiliary object class to allow URIs, including URLs, to be stored in
 directory entries in a standard way.

Background and Intended Usage

 Uniform Resource Locators (URLs) as defined by [1] are the first of
 several types of Uniform Resource Identifiers (URIs) being defined by
 the IETF.  URIs are widely used on the Internet, most notably within
 Hypertext Markup Language [2] documents. This document defines an
 X.500 [3,4] attribute type called labeledURI and an auxiliary object
 class called labeledURIObject to hold all types of URIs, including
 URLs.  These definitions are designed for use in LDAP and X.500
 directories, and may be used in other contexts as well.

Smith Standards Track [Page 1] RFC 2079 URI Attribute Type and Object Class January 1997

Schema Definition of the labeledURI Attribute Type

 Name:             labeledURI
 ShortName:        None
 Description:      Uniform Resource Identifier with optional label
 OID:              umichAttributeType.57 (
 Syntax:           caseExactString
 SizeRestriction:  None
 SingleValued:     False

Discussion of the labeledURI Attribute Type

 The labeledURI attribute type has the caseExactString syntax (since
 URIs are case-sensitive) and it is multivalued.  Values placed in the
 attribute should consist of a URI (at the present time, a URL)
 optionally followed by one or more space characters and a label.
 Since space characters are not allowed to appear un-encoded in URIs,
 there is no ambiguity about where the label begins.  At the present
 time, the URI portion must comply with the URL specification [1].
 Multiple labeledURI values will generally indicate different
 resources that are all related to the X.500 object, but may indicate
 different locations for the same resource.
 The label is used to describe the resource to which the URI points,
 and is intended as a friendly name fit for human consumption.  This
 document does not propose any specific syntax for the label part.  In
 some cases it may be helpful to include in the label some indication
 of the kind and/or size of the resource referenced by the URI.
 Note that the label may include any characters allowed by the
 caseExactString syntax, but that the use of non-IA5 (non-ASCII)
 characters is discouraged as not all directory clients may handle
 them in the same manner.  If non-IA5 characters are included, they
 should be represented using the X.500 conventions, not the HTML
 conventions (e.g., the character that is an "a" with a ring above it
 should be encoded using the T.61 sequence 0xCA followed by an "a"
 character; do not use the HTML escape sequence "&aring").

Examples of labeledURI Attribute Values

 An example of a labeledURI attribute value that does not include a

Smith Standards Track [Page 2] RFC 2079 URI Attribute Type and Object Class January 1997

 An example of a labeledURI attribute value that contains a tilde
 character in the URL (special characters in a URL must be encoded as
 specified by the URL document [1]).  The label is "LDAP Home Page":
  LDAP Home Page
 Another example.  This one includes a hint in the label to help the
 user realize that the URL points to a photo image. Rennes [photo]

Schema Definition of the labeledURIObject Object Class

 Name:              labeledURIObject
 Description:       object that contains the URI attribute type
 OID:               umichObjectClass.15 (
 SubclassOf:        top
 MayContain:        labeledURI

Discussion of the labeledURIObject Object Class

 The labeledURIObject class is a subclass of top and may contain the
 labeledURI attribute.  The intent is that this object class can be
 added to existing directory objects to allow for inclusion of URI
 values.  This approach does not preclude including the labeledURI
 attribute type directly in other object classes as appropriate.

Security Considerations

 Security considerations are not discussed in this memo, except to
 note that blindly inserting the label portion of a labeledURI
 attribute value into an HTML document is not recommended, as this may
 allow a malicious individual to include HTML tags in the label that
 mislead viewers of the entire document in which the labeledURI value
 was inserted.


 Paul-Andre Pays, Martijn Koster, Tim Howes, Rakesh Patel, Russ
 Wright, and Hallvard Furuseth provided invaluable assistance in the
 creation of this document.
 This material is based in part upon work supported by the National
 Science Foundation under Grant No. NCR-9416667.

Smith Standards Track [Page 3] RFC 2079 URI Attribute Type and Object Class January 1997

Appendix: The labeledURL Attribute Type (Deprecated)

 An earlier draft of this document defined an additional attribute
 type called labeledURL.  This attribute type is deprecated, and
 should not be used when adding new values to directory entries.  The
 original motivation for including a separate attribute type to hold
 URLs was that this would better enable efficient progammatic access
 to specific types of URIs.  After some deliberation, the IETF-ASID
 working group concluded that it was better to simply have one
 attribute than two.
 The schema definition for labeledURL is included here for historical
 reference only.  Directory client software may want to support this
 schema definition (in addition to labeledURI) to ease the transition
 away from labeledURL for those sites that are using it.
 Name:             labeledURL
 ShortName:        None
 Description:      Uniform Resource Locator with optional label
 OID:              umichAttributeType.41 (
 Syntax:           caseExactString
 SizeRestriction:  None
 SingleValued:     False
 OID:              umichAttributeType.41 (


 [1] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
 Resource Locators (URL)", RFC 1738, CERN, Xerox Corporation,
 University of Minnesota, December 1994.
 [2] Berners-Lee, T., and D. Connolly, "Hypertext Markup Language -
 2.0", RFC 1866, <URL:>
 [3] The Directory: Overview of Concepts, Models and Service.  CCITT
 Recommendation X.500, 1988.
 [4] Information Processing Systems -- Open Systems Interconnection --
 The Directory: Overview of Concepts, Models and Service.  ISO/IEC JTC
 1/SC21; International Standard 9594-1, 1988.

Smith Standards Track [Page 4] RFC 2079 URI Attribute Type and Object Class January 1997

Author's Address

 Mark Smith
 Netscape Communications Corp.
 501 E. Middlefield Rd.
 Mountain View, CA 94043, USA
 Phone:  +1 415 937-3477

Smith Standards Track [Page 5]

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