Semantic Location
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semantic location




Salil Pradhan, Glenn Steiner
Internet and Mobile Systems Laboratory
Hewlett-Packard Laboratories
1501 Page Mill Road
Palo Alto, CA 94304, USA


Mobile web-services often use location information for service customization. Most such services operate on the user's physical/geographical location. Unfortunately, such common forms of location carry little context information. In the CoolTown project at HP labs, we have addressed this deficiency by defined an orthogonal form of location - Semantic location. Use of this form of location can also help lower the risk of invasion of privacy.


Semantic location, semantic web, Pervasive Computing, location awareness, privacy, Ubiquitous Computing.

1 Introduction

Location information is an important service customization parameter for mobile web-services. The most common forms of representing location information are physical and geographical. In particular, absolute physical location is the form of choice for most positioning devices such as GPS receivers. However, it is not easy for humans to express and comprehend1 a <latitude, longitude> pair. Even with an accurate absolute physical location of a passenger traveling on a public transport bus, a service may not be able to conclusively determine the bus's route number. As a result, the service cannot offer richer services like estimating the time-of-arrival at the passenger's destination.

The city of Palo Alto will be recognized by those interested in technology as an important city in the San Francisco bay area. However, a person who has never heard of that city won't know where it is. City and other common location descriptions such as zip codes and postal addresses convey physical location as well as certain implicit semantics. Such geographical location representations are useful for services requiring explicit user input, as they are easier for people to remember and communicate. However, this representation format can be ambiguous, difficult to sense with devices and too coarse for many applications. Geographic location representation carries more semantic information than physical but there is still not enough information in either representation to determine the nature or purpose of a place.

To address these issues, we have defined an orthogonal form of location - Semantic location.

2 Semantic location

Physical locations specify the position of places [2] or points based on a global coordinate system. Geographical locations are organized hierarchically. E.g., Palo-Alto is contained in California, which in turn is part of the United States. Among other things, they signify an area or boundary usually governed by a common law. However, it's not easy to extend or define a new location, especially if it is just for e-commerce.

Figure 1

Figure 1(from left to right) Physical location - grid based, Geographical - hierarchical, Semantic - web like

Semantic location is an orthogonal form of location representation, in which a place is represented by a URI [5]. Besides a URI, links to a place can have other attributes, perhaps even the physical/geographical location of the place. The relationship between semantic locations is best described as "web-like".

Figure 2Semantic locations are unambiguous (URIs are by definition unique), user definable, extendable, and machine as well as human readable.

This approach of associating semantic attributes to a link is similar to the approach taken by the Resource Description Framework [8] and the Semantic Web [9] projects at the WWW Consortium. According to Tim Berners-Lee, most information on the Web is designed for human consumption. The Semantic Web approach is to develop languages for expressing information on the web in a machine processable form.




Annotating places with semantics

In their paper, Scalable and Flexible Location-Based Services for Ubiquitous Information Access [3], Jose and Davies from University of Minho and Lancaster University respectively present a generic architecture for building location-based applications. The emphasis of this work is on translating a physical location into semantic information. Using their location-based service infrastructure Jose and Davies have built a tourist guide application.

While building similar applications like the CoolTown WebBus, [4] we realized that this approach of mapping semantics to a physical location is particularly suitable for open areas that are covered by cellular, GPS and other physical positioning technologies. GPS usually does not work indoor and besides the positioning accuracy may not be sufficient for many applications2. Proximity sensing technologies are of great value indoors but may be impractical in a large open area.

In the CoolTown project, our approach is to label places with URLs [5] and to use standard web infrastructure to link and access them. This also allows us to use a diverse set of technologies to annotate places with URLs and sense them. Some of the technologies we have explored include:

Beacons: A CoolTown beacon broadcasts a semantic location. Typically, the range of the broadcast is determined by the Beacon's physical network technology. General, this range should be short enough to confine the overlap between places. Short-range wireless technologies such as Infrared or Bluetooth [7] are suitable physical network technologies for implementing Beacons. CoolTown beacons are configured to transmit an XML string to any sensor that comes within range. The XML string includes the relevant semantic attributes and a URL representing the associated place.

Bar Codes: We [6] are also exploring the notion of encoding URLs in variable length barcodes. Such URL could be extracted by directly scanning the barcode. Of course, existing barcodes such as UPC will need to be scanned and then resolved in the network before a URL can be obtained.

Mapping from Physical location: This approach is similar to [3]. A trusted mapping service translates a nomadic user's physical location into a URL. This service will be described in a separate paper.


While on-board a public transport bus, John uses his PDA to receive a URL from a beacon and browses the site. Figure 3This URL includes the bus route and a snapshot of the bus' current physical location. With this information, the service offers richer services like estimating the time-of-arrival at San Jose bus terminal.

3 Privacy and Safety

With popular service models, a mobile user's physical location and unique identifier are criterion used to provide personalized service. While at a bus stop, if a commuter equipped with a WAP enabled cellular phone wanted to search for the nearest starbucks, she would have to provide her current physical location (positioned using cellular triangulation or GPS) to a location based search engine. Along with privacy concerns, this also raises safety concerns. Unscrupulous services may sell not only her online-profile but also her physical whereabouts tracked through the day. With the CoolTown approach, the commuter's phone could receive a URL emitted by a bus stop beacon and browse the site. The web service at that URL is aware of the physical location of the bus stop and can assist the user in her quest for the nearest starbucks without asking for her current physical location. The web service cannot conclusively pinpoint her physical location; using the web site does not imply that she is at the bus stop.

It is not always possible to populate all places with beacons and therefore mapping from a physical location to a URL may be required. Again, the CoolTown approach is useful; a trusted vendor can provide the mapping while the resulting semantic location could be handled by other services. Since a] a reverse mapping from semantic location to physical location is not always guaranteed to result in a unique result and b] use of a semantic location does not imply presence at a particular physical location, potentially unscrupulous web services cannot conclusively track their user's physical movements.

4 Summary

A user's location is an important service customization criterion. The most common forms of location representation are physical and geographical. In CoolTown, we have explored another form, semantic location.

Semantic locations are globally uniform, unambiguous (URIs are by definition unique) and links to them can carry as much semantic information as required. They are represented by URLs, and are linked and accessed using standard web infrastructure. This is a highly scalable approach as there is no central control point. Depending on the application, the place, and the desired accuracy, one of the many URL sensing technologies can be selected. Even at a single place, a heterogeneous set of technologies can be deployed.

Visiting a semantic location does not imply physical presence at the associated place. This impedes the ability of mobile e-services to conclusively track the physical movements of nomadic users, without restricting their ability to provide localized service.

The CoolTown project includes a number of people at HP Labs. The people working on location based services include Salil Pradhan, Venky Krishnan, Gene Becker, Debbie Caswell, Philippe Debaty, Gita Gopal, Glenn Steiner, Tim Kindberg, John Barton, Steve Loughran, Jeff Morgan, Wei-Ying Ma, Miranda Mowbray, Mirjana Spasojevic, Mike Spratt, Ed MacDonald & Steve Wright.


[1] The US postal service doesn't deliver letters marked with just a latitude and longitude.
[2] For Example, sensing that a visitor is viewing a particular exhibit in the Smithsonian Museum.


[1] Venky Krishnan et al. Location Awareness in HP's CoolTown.
[2] Debbie Caswell. Creating a web representation for Places.
[3] Jose, R. and N. Davies. Scalable and Flexible Location-Based Service for Ubiquitous Information Access, Handheld and Ubiquitous Computing; Proceeding from the First International Symposium, HUC'99, Karlsruhe, Germany, September 1999.
[4] CoolTown home page.
[5] WWW Names and Addresses: URIs, URLs, ...
[6] Tim Kindberg and John Barton. Private Communication. HP Laboratories.
[7] Bluetooth home page.
[8] Resource Description Framework. [9] Tim Berners-Lee. Semantic Web.






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