Network Working Group M. Thomson Request for Comments: 5139 J. Winterbottom Updates: 4119 Andrew Category: Standards Track February 2008
Revised Civic Location Format for Presence Information Data Format Location Object (PIDF-LO)
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.
This document defines an XML format for the representation of civic location. This format is designed for use with Presence Information Data Format Location Object (PIDF-LO) documents and replaces the civic location format in RFC 4119. The format is based on the civic address definition in PIDF-LO, but adds several new elements based on the civic types defined for Dynamic Host Configuration Protocol (DHCP), and adds a hierarchy to address complex road identity schemes. The format also includes support for the xml:lang language tag and restricts the types of elements where appropriate.
Since the publication of the original PIDF-LO civic specification, in [RFC4119], it has been found that the specification is lacking a number of additional parameters that can be used to more precisely specify a civic location. These additional parameters have been largely captured in [RFC4776].
This document revises the GEOPRIV civic form to include the additional civic parameters captured in [RFC4776]. The document also introduces a hierarchical structure for thoroughfare (road) identification, which is employed in some countries. New elements are defined to allow for even more precision in specifying a civic location.
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].
The term "thoroughfare" is used in this document to describe a road or part of a road or other access route along which a final point is identified. This is consistent with the definition used in [UPU-S42].
[RFC4776] provides a full set of parameters that may be used to describe a civic location. Specifically, [RFC4776] lists several civic address types (CAtypes) that require support in the formal PIDF-LO definition that are not in [RFC4119].
These changes include new elements that are required to support more complex structures for naming street addresses. This is described in more detail in Section 3.2.
In some countries, a thoroughfare can be broken up into sections, and it is not uncommon for street numbers to be repeated between sections. A road section identifier is required to ensure that an address is unique. For example, "West Alice Parade" in the figure below has 5 sections, each numbered from 1; unless the section is specified, "7 West Alice Parade" could exist in 5 different places. The "RDSEC" element is used to specify the section.
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Minor streets can share the same name, so that they can only be distinguished by the major thoroughfare with which they intersect. For example, both "West Alice Parade, Section 3" and "Bob Street" could both be intersected by a "Carol Lane". The "RDBR" element is used to specify a road branch where the name of the branch does not uniquely identify the road. Road branches MAY also be used where a major thoroughfare is split into sections.
Similar to the way that a road branch is associated with a road, a road sub-branch is associated with a road branch. The "RDSUBBR" element is used to identify road sub-branches.
The "A6" element is retained for use in those countries that require this level of detail. Where "A6" was previously used for street names in [RFC4119], it MUST NOT be used; the "RD" element MUST be used for thoroughfare data.
The following figure shows a fictional arrangement of roads where these new thoroughfare elements are applicable.
| || | ---------------|| | Carol La. Carol La. || Bob | || St. | West Alice Pde. || ==========/=================/===============/==========||=========== Sec.1 Sec.2 Sec.3 | Sec.4 || Sec.5 | || ----------| Carol || Alley 2 | La. || | ||
The introduction of new thoroughfare elements affects the interpretation of several aspects of more specific civic address data. In particular, street numbering (the "HNO" element) applies to the most specific road element specified, that is, the first specified element from "RDSUBBR", "RDBR", "RDSEC", or "RD".
The "PRM", "POM", "PRD", "POD", and "STS" elements always apply to the value of the "RD" element only. If road branches or sub-branches require street suffixes or qualifiers, they MUST be included in the "RDBR" or "RDSUBBR" element text.
The "A1" element is used for the top-level subdivision within a country. In the absence of a country-specific guide on how to use the A-series of elements, the second part of the ISO 3166-2 code [ISO.3166-2] for a country subdivision SHOULD be used. The ISO 3166-2 code is formed of a country code and hyphen plus a code of one, two, or three characters or numerals. For the "A1" element, the leading country code and hyphen are omitted and only the subdivision code is included.
For example, the codes for Canada include CA-BC, CA-ON, CA-QC; Luxembourg has just three single-character codes, LU-D, LU-G, and LU-L; Australia uses both two- and three-character codes, AU-ACT, AU-NSW, AU-NT; and France uses numerical codes for mainland France and letters for territories, FR-75, FR-NC. This results in the following fragments:
The XML schema defined for civic addresses allows for the addition of the "xml:lang" attribute to all elements except "country" and "PLC", which both contain language-neutral values. The range of allowed values for "country" is defined in [ISO.3166-1]; the range of allowed values for "PLC" is described in the IANA registry defined by [RFC4589].
The "script" field defined in [RFC4776] is omitted in favor of using the "xml:lang" attribute with a script subtag [RFC4646].
It is RECOMMENDED that each "civicAddress" element use one language only, or a combination of languages that is consistent. Where a civic location is represented in multiple languages, multiple "civicAddress" elements SHOULD be included in the PIDF-LO document.
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For civic addresses that form a complex to describe the same location, these SHOULD be inserted into the same tuple.
The DHCP format for civic addresses [RFC4776] permits the inclusion of an element multiple times with different languages or scripts. However, this XML form only permits a single instance of each element. Multiple "civicAddress" elements are required if any element is duplicated with different languages. If the same language and script are used for all elements, or no elements are duplicated, the format can be converted into a single civic address.
Where there are duplicated elements in different languages, a "civicAddress" element is created for each language that is present. All elements that are in that language are included. Elements that are language independent, like the "country" and "PLC" elements, are added to all "civicAddress" elements.
3.5.2. Combining Multiple Elements Based on Language Preferences
If the receiver of the XML representation is known, and that receiver has indicated language preferences, a single XML format can be constructed using those preferences. For example, language preferences can be indicated by the "Accept-Language" header in the SIP or HTTP protocols.
All elements that have only one value, irrespective of language, are used. Where multiple values exist, each value is assigned a weighting based on the language preferences. The value with the highest weighting is selected. An arbitrary value is selected if two values have the same preference, if there is no preference for the available languages, or if there are conflicting values with the same language.
The XML schema [W3C.REC-xmlschema-2-20041028] defined in Section 4 uses a base type of "token" instead of "string" as used in [RFC4119].
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The "token" type ensures that whitespace within instance documents is normalized and collapsed before being passed to a processor. This ensures that the following fragments are considered equivalent by XML processors:
<A1> North Wollongong </A1>
Whitespace may still be included in values by using character references, such as " ".
The XML representation described in this document is designed for inclusion in a PIDF-LO document. As such, it is subject to the same security considerations as are described in [RFC4119]. Considerations relating to the inclusion of this representation in other XML documents are outside the scope of this document.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object Format", RFC 4119, December 2005.
[RFC4589] Schulzrinne, H. and H. Tschofenig, "Location Types Registry", RFC 4589, July 2006.
[RFC4646] Phillips, A. and M. Davis, "Tags for Identifying Languages", BCP 47, RFC 4646, September 2006.
[RFC4776] Schulzrinne, H., "Dynamic Host Configuration Protocol (DHCPv4 and DHCPv6) Option for Civic Addresses Configuration Information", RFC 4776, November 2006.
[ISO.3166-1] International Organization for Standardization, "Codes for the representation of names of countries and their subdivisions - Part 1: Country codes", ISO Standard 3166- 1:1997, 1997.
[ISO.3166-2] International Organization for Standardization, "Codes for the representation of names of countries and their subdivisions - Part 2: Country subdivision code", ISO Standard 3166-2:1998, 1998.
The authors would like to thank Henning Schulzrinne for his assistance in defining the additional civic address types, particularly his research into different addressing schemes that led to the introduction of the thoroughfare elements. Rohan Mahy suggested the ISO 3166-2 recommendation for A1. In addition, we would like to thank Jon Peterson for his work in defining the PIDF-LO.
Martin Thomson Andrew PO Box U40 Wollongong University Campus, NSW 2500 AU
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