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
<draft-morris-geopriv-location-object-issues-00.txt>
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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
2002:
(1) Should geopriv facilitate the misrepresentation of location
information?
(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
technologies).
(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
Representations"
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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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The use of Multiple Locations in the LO June 2002
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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The use of Multiple Locations in the LO June 2002
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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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
Germany
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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