GEOPRIV J. Winterbottom
Internet-Draft M. Thomson
Intended status: Standards Track Andrew Corporation
Expires: September 8, 2011 R. Barnes
BBN Technologies
B. Rosen
NeuStar, Inc.
R. George
Huawei Technologies
March 7, 2011
Specifying Civic Address Extensions in PIDF-LO
draft-ietf-geopriv-local-civic-00
Abstract
New fields are occasionally added to civic addresses. A backwardly-
compatible mechanism for adding civic address elements to the Geopriv
civic address format is described. A formal mechanism for handling
unsupported extensions when translating between XML and DHCP civic
address forms is defined for entities that need to perform this
translation.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivating Example . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Specifying Civic Address Extensions . . . . . . . . . . . . . 4
3. Translating Unsupported Elements . . . . . . . . . . . . . . . 5
3.1. XML to DHCP Format Translation . . . . . . . . . . . . . . 6
3.2. Extension Civic Address Type (CAtype) . . . . . . . . . . 6
3.3. DHCP to XML Format Translation . . . . . . . . . . . . . . 7
3.4. Conversion Example . . . . . . . . . . . . . . . . . . . . 7
4. Civic Extensions . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Pole Number . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Mile Post . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3. Street Type Prefix . . . . . . . . . . . . . . . . . . . . 9
4.4. House Number Prefix . . . . . . . . . . . . . . . . . . . 9
4.5. XML Extension Schema . . . . . . . . . . . . . . . . . . . 10
4.6. Extension examples . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6.1. CAtype Registration for Extensions . . . . . . . . . . . . 11
6.2. End of Numeric CAtype Registration . . . . . . . . . . . . 11
6.3. URN sub-namespace registration for
'urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr:ext' . . 11
6.4. XML Schema Registration . . . . . . . . . . . . . . . . . 12
6.5. Registration Template . . . . . . . . . . . . . . . . . . 12
6.6. Registration Policy and Expert Guidance . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
The Geopriv civic location specifications ([RFC4776], [RFC5139])
define an XML and binary representtations for civic addresses that
allow for the expression of civic addresses. Guidance for the use of
these formats for the civic addresses in different countries is
included in [RFC5774].
Subsequent to these specifications being produced, use cases for
extending the civic address format with new elements have emerged.
Extension elements do not readily fit existing elements, as
recommended in [RFC5774].
The XML format for civic addresses [RFC5139] provides a mechanism
that allows for the addition of standardized or privately understood
elements. A similar facility for private extension is not provided
for the DHCP format [RFC4776], though new specifications are able to
define new CAtypes (civic address types).
A recipient of a civic address in either format currently has no
option other than to ignore elements that it does not understand.
This results in any elements that are unknown to that recipient being
discarded if a recipient performs a translation between the two
formats. In order for a new extension to be preserved through
translation by any recipient, the recipient has to understand the
extension and know how to correlate an XML element with a CAtype.
This document describes how new civic address elements are added.
Extension always starts with the definition of XML elements. A
mechanism for carrying the extension in the DHCP format is described.
A new XML namespace containing a small number of additional civic
elements is also defined and can be used as a template to illustrate
how other extensions can be defined as required.
These mechanisms ensure that any translation between formats can be
performed consistently and without loss of information. Translation
between formats can occur without knowledge of every extension that
is present.
These additions described in this document are backwardly compatible.
Existing implementations may cause extension information to be lost,
but the presence of extensions does not affect an implementation that
conforms to either [RFC4776] or [RFC5139].
1.1. Motivating Example
One instance where translation might be necessary is where a device
receives location configuration using DHCP [RFC4776]. Conversion of
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DHCP information to an XML form is necessary if the device wishes to
use the DHCP-provided information in a range of applications,
including location-based presence services [RFC4079], and emergency
calling [RFC5012].
+--------+ +--------+ +-----------+
| DHCP | DHCP | Device | XML | Recipient | e.g., Presence
| Server |--------->| |-------->| | Agent
+--------+ +--------+ +-----------+
Conversion Scenario
The Device that performs the translation between the DHCP and XML
formats might not be aware of some of the extensions that are in use.
Without knowledge of these extensions and how they are represented in
XML, the Device is forced to discard them.
These extensions could be useful - or critical - to the ultimate
consumers of this information. For instance, an extension element
might provide a presence watcher with important information in
locating the Device or an extension might be significant in choosing
a particular call route.
1.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Specifying Civic Address Extensions
The civic schema in [RFC5139] defines an ordered structure of
elements that can be combined to describe a civic address. The XML
extension point at the end of this sequence is used to extend the
address.
New elements are defined in a new XML namespace [XMLNS]. This is
true of address elements with significance within private or
localized domains, as well as those that are intended for global
applicability.
New elements SHOULD use the basic "caType" schema type defined in
[RFC5139]. This type provides an optional "xml:lang" attribute.
For example, suppose the (fictitious) Central Devon Canals Authority
wishes to introduce a new civic element called "bridge". The
authority defines an XML namespace that includes a "bridge" element.
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The namespace needs to be a unique URI, for example
"http://devon.canals.org.uk/civic".
A civic address that includes the new "bridge" element is shown in
Figure 1.
See RFCXXXX.
END 6.4. XML Schema Registration This section registers an XML schema as per the procedures in [RFC3688]. URI: urn:ietf:params:xml:schema:pidf:geopriv10:civicAddr:ext Registrant Contact: IETF, GEOPRIV working group, (geopriv@ietf.org), James Winterbottom (james.Winterbottom@andrew.com). The XML for this schema can be found as the entirety of Section 4.5 of this document. 6.5. Registration Template New registrations in the "CAtypes" registry require the following information: CAtype: The assigned numeric CAtype. All new registrations use the value XX. [[IANA/RFC-Editor: update XX] Existing registrations use their assigned value. Winterbottom, et al. Expires September 8, 2011 [Page 12] Internet-Draft Civic Extensions March 2011 Namespace URI: A unique identifier for the XML namespace used for the extension element. Local Name: The local name of an XML element that carries the civic address element. Description: A brief description of the semantics of the civic address element. (Optional) Example: One or more simple examples of the element. Contact: Contact details for the person providing the extension. (Optional) Specification: A reference to a specification for the civic address element. (Optional) Schema: A reference to a formal schema (XML schema, RelaxNG, or other form) that defines the extension. Registrations from [RFC4776] and [RFC5139] are registered with the following form: CAtype: (The existing CAtype.) Namespace URI: urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr Local Name: (The contents of the PIDF column.) Description: (The existing description for the element, including a note about the equivalent NENA field, if present.) Contact: The IESG (iesg@ietf.org); the GEOPRIV working group (geopriv@ietf.org). Specification: RFC4776 and RFC5139 Schema: urn:ietf:params:xml:schema:pidf:geopriv10:civicAddr Registration of the schema defined in this document in Section 4.5. CAtype: The assigned numeric CAtype value is XX. [[IANA/RFC-Editor: update XX] Namespace URI: urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr:ext Winterbottom, et al. Expires September 8, 2011 [Page 13] Internet-Draft Civic Extensions March 2011 Local Name: PN, MP, STP, HNP Description: PN: Post number that is attributed to a lamp post or utility pole. Description: MP: Mile Post a marker indicating distance to or from a place (often a town). Description: STP: Street Type Prefix. Description: HNP: House Number Prefix. Contact: The IESG (iesg@ietf.org); the GEOPRIV working group (geopriv@ietf.org). Specification: RFCXXXX [[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX with the RFC number for this specification.]] Schema: urn:ietf:params:xml:schema:pidf:geopriv10:civicAddr:ext 6.6. Registration Policy and Expert Guidance The "CAtypes" registry is altered to operate on a registration policy of "Expert Review", and optionally "Specification Required" [RFC5226]. The registration rules for "Specification Required" are followed only if a registration includes a reference to a specification. Registrations can be made without a specification reference. All registrations are reviewed to identify potential duplication between registered elements. Duplicated semantics are not prohibited in the registry, though it is preferred if existing elements are used. The expert review is advised to recommend the use of existing elements following the guidance in [RFC5774]. Any registration that is a duplicate or could be considered a close match for the semantics of an existing element SHOULD include a discussion of the reasons that the existing element was not reused. 7. Acknowledgements Thanks to anyone who has tried to extend the civic schema and found it a little unintuitive. 8. References Winterbottom, et al. Expires September 8, 2011 [Page 14] Internet-Draft Civic Extensions March 2011 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. [RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration Information", RFC 4776, November 2006. [RFC5139] Thomson, M. and J. Winterbottom, "Revised Civic Location Format for Presence Information Data Format Location Object (PIDF-LO)", RFC 5139, February 2008. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [XMLNS] Hollander, D., Layman, A., Tobin, R., and T. Bray, "Namespaces in XML 1.1 (Second Edition)", World Wide Web Consortium Recommendation REC-xml-names11-20060816, August 2006,