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Internet Draft                                      John B.  Morris, Jr.
                                     Center for Democracy and Technology

                                                             J.  Cuellar
                                                              Siemens AG

                                                               A.  Gogic
                                                          QUALCOMM, Inc.

                                                            D.  Mulligan
                                                            A.  Burstein
                     Samuelson Law, Technology, and Public Policy Clinic

Expires: Dec. 2002                                             June 2002

          The use of Multiple Locations in the Location Object


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

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               The use of Multiple Locations in the LO      June 2002

                             Table of Contents

   1. Abstract.......................................................2
   2. Summary........................................................2
   3. Conventions Used in This Document..............................3
   4. Underlying Assumptions.........................................3
      4.1. Location Representation in the Location Object............4
      4.2. Location Representation Format............................4
      4.3. Provisions for Precision and Confidence...................4
      4.4. Multiple Representations of a Single Location.............5
   5. User-controlled Precision of Location Representation...........5
   6. Misstatement of Location Information...........................5
   7. Multiple Locations.............................................6
      7.1. General Principles........................................6
      7.2. The Semantics of Multiple Locations within a Single Object 6
   8. Acknowledgements...............................................7
   9. References.....................................................7
   10. Author's Addresses............................................7
   11. Full Copyright Statement......................................7

1. Abstract

   This document discusses three major questions that were posed and
   discussed at some length at the interim meeting in San Diego, June

   (1) Should geopriv facilitate the misrepresentation of location

   (2) Should the geopriv Location Object (LO) accommodate multiple
   locations as part of a single positioning transaction?

   (3) If so, should the Location Object hold multiple locations in a
   single object, or should the multiple locations be contained in
   multiple objects?

   In this paper we propose an answer to those questions.

2. Summary

   In this paper we propose the following:

   (1) Geopriv should not facilitate the misrepresentation of location
   information (but it should also not try to prohibit it).

   (2) The protocol should allow multiple Locations within one Location
   Object, meaning that the intended location is one of the Locations
   included in the LO.

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               The use of Multiple Locations in the LO      June 2002

   (3) Further each Location may contain different representations of
   the location (for instance, the results of different measuring

   (4) An application may use multiple locations contained in multiple
   objects if desired.

   The relationship between LO, Locations and Location Representations
   may be seen schematically as follows: The Location Object MAY contain
   zero, one, or several Locations (= Location Fields) L1, L2, etc:

   LO =
   |  ID  | Cred |  ..  |  L1  |  ..  |  Li  |  ..    |  Ln  |
                        \_______________  ___________________/
                                Location Information

   The intended semantics of the Location Information is then that one
   of the Li is

     Location Information = L1 or L2 or ... Ln

   in the sense that the Location Information "holds" (for whatever
   purpose the using protocol uses the location) exactly if one location
   Li "holds".

   Further, a Location (field) Li is MAY contain different "Location

   Li (i=1,.., n)  =
   |  LRi1  |  LRi2  |   LRi3 |  ..    |   LRim |

   The intended semantics of a Location Li is

     Li = LRi1 and LRi2 and ... LRim

   in the sense that location Li "holds" (for whatever purpose the using
   protocol uses the location) exactly if all location representations
   LRij "hold".

3. Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [KEYWORDS].

4. Underlying Assumptions

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   The following are are assumptions on which the later questions are in
   part based.

4.1. Location Representation in the Location Object

   Each Location Object (LO) MAY contain one or several representations
   of location in a single specified format. But a LO does not have to
   contain one Location. For instance it may be just a query for a
   Location or an Authorization Credential or for some negotiation.

4.2. Location Representation Format

   To ensure interoperability at least one specific format (to be
   determined by the group) will be selected to express a location
   representation. Any geopriv conformant implementation MUST support
   this format. (Probably this specific format will support different
   levels of precision.) The geopriv specification MAY define other
   formats that the implementations SHOULD support. One possible common
   format could be latitude, longitude, altitude triplet (LAT, LON,
   ALT).  This format is quite universal and independent of potentially
   elaborate and dynamic databases.  Perhaps another choice of format,
   for instance one of the formats developed by LIF, OpenGIS, 3GPP, or
   another organization should be adopted.

4.3. Provisions for Precision and Confidence

   Each location representation contained in the LO MAY include elements
   for precision and confidence.  But the precision (accuracy) is
   perhaps part of the format itself, not an extra field in the LO.  On
   the other hand, confidence is not usually a parameter of the format
   itself.  Thus, while precision will be probably not an extra field in
   the LO, confidence will be out of scope or a field associated with a
   representation in a LO.
   The "precision" of a location measurement indicates an area within
   which a target is located, with a given degree of confidence.  For
   example, if the location of a target is known with certainty to be
   within a rectangular region that is five kilometers wide and 10
   kilometers long, then 50 square kilometers gives a measure of the
   precision with which the target's location is known.  "Confidence,"
   on the other hand, indicates the level of reliability given to each
   location indication.  The confidence level of a given location
   measurement indicates the probability that the target is actually
   located within a certain area around a specific point.

   As seen from this example, precision may in principle be indicated by
   any arbitrarily shaped area.  A commonly used undiluted precision
   indication is a circle, and is conveyed by linear distance (expressed
   in meters) from the location datum in which measurement confidence
   reaches its peak.  Thus, as an example, it may be said that the LO is
   at (LAT = 47 deg 15 min 29 sec, LON = 15 deg 39 min 53 sec), with
   precision of 25 meters, and confidence of 67%.  Other simple commonly
   used areas are ellipses.

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   As we shall see from a later discussion, precision with which
   location is conveyed to a client may be intentionally diluted by
   broadening the precision area, which then is termed "granularity".

4.4. Multiple Representations of a Single Location

   A LO MAY contain multiple representations of the same location.  A
   single location can be expressed within the LO in more than one
   format, such as a latitude-longitude pair, a postal address, or a
   political entity, such as a province or country.

   Multiple representations fulfill several purposes.  First, multiple
   representations can provide more useful or understandable forms of
   location information to applications or Location Recipients.
   Multiple representations can also provide guidance for user-supplied
   location information.  Finally, multiple representations of a single
   location can reflect multiple measurements of the same location.
   These differences might arise from discrepancies among different
   measuring devices or technologies.  Thus, for a given location, a LO
   might include the results of a GPS calculation and a triangulation
   off of cellular transmitter towers.  Results of two measurements in
   most cases will not be precisely the same, but the LO will view them
   as multiple representations of the same location and allow the
   application to determine how best to handle the two representations.

5. User-controlled Precision of Location Representation

   The geopriv protocol MUST allow a user to control the precision of
   location information.  There are many reasons that this control is
   desirable or necessary, and the LO cannot permit some representations
   while refusing others.  To distinguish between user controlled
   precision and measurement precision, it is advised that the former be
   named "granularity".

   If location information is provided with diluted granularity, it MUST
   contain the optional precision parameter discussed earlier.

6. Misstatement of Location Information

   The geopriv protocol MUST not create the assumption that the location
   returned to a requester is either truthful or deceptive.  Although
   the geopriv protocol should not explicitly facilitate the
   misstatement of location information, it should also not prohibit it.
   This neutrality would provide utility for many kinds of uses, and
   would preclude the need for elaborate technology to distinguish
   misstated locations from truthful ones.  This implicitly means that
   optional precision and confidence parameters may also be misstated.
   The issue may be a subject for further discussion.

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   Providing misstated (deceptive) information may be one of the
   available tools to guard LO owner's privacy.  However, use of
   misstated location information is not endorsed as a preferred means
   for guarding privacy, and providers of misstated information should
   be warned of potential pitfalls.  We suggest that control of
   precision (granularity) of location should be viewed as a primary
   tool for guarding privacy.

7. Multiple Locations

7.1. General Principle

   Geopriv should support the expression of multiple locations within a
   single transaction.

7.2. The Semantics of Multiple Locations within a Single Object

   The geopriv object cannot be confined to have only one meaning --in
   many cases it may be the representation of the actual position of the
   target at the time of transmission.  There are other possible
   meanings, such as planned trajectory of travel, beginning and end of
   a vehicle (such as train) where target is located, etc.

   "If multiple location within a single objects are used, there should
   be implied semantics that the object's location is in one of the
   following locations, i.e. they are connected with an OR".

   At the interim meeting the following four approaches were discussed:

      o The geopriv protocol should not handle multiple locations at
         all.  A transaction may involve only one LO, and that LO
         contains only one location.  Note that it is still feasible
         with this approach to define a more complex semantics around
         an object by means of a higher layer protocol.

      o The geopriv LO may contain multiple locations, with the
         required interpretation that multiple locations mean "the
         intended location is at most one of the following locations."

      o Same as above, but the LO will permit a field to specify how
         the multiple locations are to be related, that is, with ORs,
         ANDs, etc.  This approach, although theoretically possible,
         may be too difficult to implement, since possible
         relationships can be too complex to convey in a single field.

      o The LO must contain only one location, but may contain a flag
         that signifies that the LO does not completely specify the
         intended location.

   We propose that geopriv should use the second approach to allowing
   multiple locations.

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               The use of Multiple Locations in the LO      June 2002

8. Acknowledgements

   We wish to thank the members of the IETF geopriv WG for their
   comments and suggestions.  Detailed comments or text were provided by
   Randall Gellens and other the participants of the geopriv interim
   meeting in San Diego.

9. References

   [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
          Levels", BCP 14, RFC 2119, March 1997.

10. Author's Addresses

   Jorge R Cuellar
   Siemens AG
   Corporate Technology
   CT IC 3
   81730 Munich                   Email:  Jorge.Cuellar@mchp.siemens.de

   John B.  Morris, Jr.
   Director, Internet Standards, Technology & Policy Project
   Center for Democracy and Technology
   1634 I Street NW, Suite 1100
   Washington, DC 20006                         Email:  jmorris@cdt.org
   USA                                               http://www.cdt.org

   Aleksandar M. Gogic
   QUALCOMM, Incorporated
   5775 Morehouse Drive
   San Diego, CA 92121-1714
   USA                                      Email:  agogic@qualcomm.com

   Aaron Burstein
   Samuelson Law, Technology and Public Policy Clinic
   Boalt Hall School of Law
   University of California
   Berkeley, CA 94720-7          Email:  burstein@boalthall.berkeley.edu

   Deirdre K.  Mulligan
   Samuelson Law, Technology and Public Policy Clinic
   Boalt Hall School of Law
   University of California
   Berkeley, CA 94720-7              Email:  dmulligan@law.berkeley.edu

11. Full Copyright Statement

   Copyright (C) The Internet Society (date).  All Rights Reserved.

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               The use of Multiple Locations in the LO      June 2002

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   This document and the information contained herein is provided on an

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