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Addressing Concepts for Mobile Location-Based Information Services Wolfgang Narzt, Gustav Pomberger, Alois Ferscha, Dieter Kolb, Reiner Müller, Horst Hörtner, and Ronald Haring Johannes Kepler University Linz, Altenbergerstr. 69, A-4040 Linz, Austria Siemens Corporate Technology, Otto-Hahn Ring 6, D-81730 Munich, Germany Ars Electronica Futurelab, Hauptstr. 2, A-4040 Linz, Austria {wolfgang.narzt, gustav.pomberger, alois.ferscha}@jku.at, {kolb.dieter, reiner.e.mueller, jan.wieghardt}@siemens.com, {horst.hoertner, roland.haring}@aec.at
Abstract. Emerging mobile location-based information services enable people to place digital content into the physical world. Based on three technical components (1) mobile devices, (2) wireless networking and (3) location-sensing the implementation of location-based services can be considered state of the art. In contrast, we observe a lack of conceptual work in terms of user interface issues, like designing indirect (one-to-any) addressing models, handling information overflow and avoiding spam. Every user is able to arbitrarily place information anywhere without structure or restrictions, and is confronted with an information mess in return. The focus of this paper concentrates on a novel addressing concept for mobile location-based information services, which systematically structures both direct and indirect addressing methods and supports the users in finding or filtering the information they are interested in. Keywords: Mobile Location-Based Services, Spam, Addressing Concepts.
1 Introduction A heterogeneous manifold of mobile devices and wireless networking technology satisfy the rapidly rising need for mobility and autonomy concerning unbounded world wide information exchange. Whereas laptop computers, personal digital assistants and mobile phones can be regarded as mature mobile device technology, the next generation of transportable perception units is close to be released from the research labs (i.e., wearable computers, head-mounted see-through displays and even tangible objects). Combined with various wireless transmission technologies, like GSM, GPRS, UMTS and WLAN these mobile devices are commonly used for synchronous (e.g., voice and video telephony) and asynchronous communication (e.g., SMS and MMS). Recently, miscellaneous location sensors (e.g., GPS, cellular triangulation, ultrasonic sensors, etc.) extend such services and enable users to annex position coordinates to messages and consequently to store information at a desired place 1611. C. Stephanidis (Ed.): Universal Access in HCI, Part II, HCII 2007, LNCS 4555, pp. 507–516, 2007. © Springer-Verlag Berlin Heidelberg 2007
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Neglecting uncertainty issues concerning positioning accuracy, limited field coverage, fragmentary wireless connectivity and power consumption, the three components mobile devices, wireless networking and location-sensing are regarded as the enabling core technologies for mobile location-based services 2. However, based upon these technical prerequisites it is necessary to develop concepts and user interaction paradigms for organizational issues concerning such services, in order to make the perception of information adequate for the users 11:
2 Organizational Issues Basically, we can identify four different organizational issues which extend or structure the pure functionality of mobile location-based information services: First, the type of addressing inevitably differs in location-based services: Information is not only delivered to a set of selected predefined phone numbers but to any receivers (e.g., distinguished by their group memberships) who locally pass by the information. Thus primarily, the type of addressing is indirect (one-to-any) implicating that the number and identity of the recipients is unknown to the author of information. Second, the context a recipient is associated with when examining information may affect his perception, meaning that e.g., information is only relevant on certain conditions or that the content of information is presented differently to the user 5. Context can be regarded as a diversified term, representing any identifiable state due to sensory input. To rise above or fall below a threshold of any technically measurable quantity may change a potential context 19. Time is a simple example of a quantifiable value allowing recipients e.g., to perceive information only during a period. Third, and closely related to the feature of context-sensitivity of mobile locationbased information services is the term smartness 16: Information is not always supposed to present static content – it can also dynamically adapt content or provide executable content for active manipulation. Basically, we distinguish three different types of smartness: (1) Information contains self-changing elements, like a ticker showing the consecutive progress of time (dynamic content). (2) The recipient himself is able to influence the content of information, e.g., by a click on a button, like in a poll where he changes statistical content by his vote (influenced content). (3) Users are able to trigger actions through interactive elements or the information itself executes code when it is perceived (executable content). Bringing smart elements to mobile location-based information services opens up the door for developing an unlimited variety of distinctive content. Consequently, the service needs an extension concept for the core functionality, which appears to be the fourth organizational issue in mobile location-based information services. An extension concept must enable third-party developers to easily design their own (smart) elements, and it has to provide a mechanism to make these self-developed elements accessible to all users without forcing them to download new software versions or to restart their system. Users should not recognize if an element has just recently been developed by a third party or if it is a basic element like plain text. These four issues addressing, context, smartness and extensibility enrich the functionality of mobile location-based information services. They are considered to represent the organizational layer, a more focused layer above the technical layer as illustrated in Fig. 1.
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Fig. 1. Layer Model
The top layer contains presentation and interaction paradigms. It uses the technical components and concepts of the layers below to adequately present information. Generally, location information can be shown in a bird’s eye view on a 2D-map, in a simple list showing only the information the user is close to or even in an augmented reality (AR) view 15. Future scenarios even dismiss conventional display metaphors. They supersede the device screen for perception and present information in an alternative manner: Text may e.g., appear acoustically or a door may open when the user approaches information without forcing the user to peer at a display. However, this paper focuses on addressing concepts in the organizational layer and gives an idea how information can be filtered by the user in the top layer.
3 Addressing Concept The classical sender-receiver model for dispatching information does not meet the requirements in mobile location-based information services, anymore. Information is enriched by location and is predominantly designated to all passers-by within a defined radius. However, if everybody is capable of placing information to any location the service will predictably become unusable due to information overflow. An exaggerated use of this service leaves the users stuck in an unstructured information mess where the entropy of most messages is null. Thus, mobile locationbased information services urgently need a flexible and structured addressing concept for avoiding scenarios like this. • An addressing concept must be capable of dealing with distinctive user communities or groups of interest for constricting the set of recipients and for avoiding spam. Users must be capable of joining communities or selecting terms of interest in order to find or filter the required information. • Self-evidently, the concept must be scalable to millions of simultaneously online users. And it must be globally expandable all over the world, in contrast to locally bordered, non-interoperable isolated solutions. The possibility for building autonomous applications should be preserved, though. • The use of smart elements enforces an extended model for access control. Information is not only characterized by read- and write-privileges, it can also define execution rights for selected users or groups.
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• Finally, the handling of the user interface must comply with simplicity paradigms. Users should not run through registration procedures to join groups or communities (although registration is sometimes inevitable for access control). Interaction should be intuitive and answer the following two requests a user might make: “I am interested in …” and “What kind of information is available here?” We first introduce the basic principles for an addressing concept that meet all the requirements stated above on the example of direct addressing, where users select one or more recipients from their private address book. Afterwards, we extend this concept to indirect one-to-any addressing based on the principles of direct addressing. 3.1 Direct Addressing Similar to mobile telecommunication services we propose a distributed provider model where users can join the provider of their choice. This proven model guarantees scalability of the service as each provider only handles a limited number of clients. Every user carries a world-wide exclusive identification number which consists of the unique identification of the provider plus an internal number: = .
The identification number grants independence from the used mobile devices and transport technology. It is the task of the provider to map this abstract number to a specific IP-address, MAC-address or phone number. The identification number is also used to mark location-based information. Messages stored at a particular provider also obtain this tuple for unambiguous identification, whereupon the second part has to be disjoint from that of the registered users: = .
A user who wants to position directly addressed information – no matter where on the earth – sends a message with an associated geo-position and the list of recipients to his provider. The provider assigns a new ID to this message and separates the message into a small header and a body. The header contains the new message ID, the location and the list of recipients. The rest (i.e., the main part of a message including text, pictures, video, sound and smart elements) is part of the body. Header and body are separately stored at the provider, and the header information is delegated to all those providers that can be identified in the tuple numbers of the recipients list. So, all involved providers of the recipients are aware of the location-based message but only the provider of the creator stores the whole content (see Fig. 2).
Fig. 2. Direct Addressing Concept
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Once, the recipient is logged in at his provider and repetitively transmits his current geo-position he continuously (but only once per message) receives header information for messages with local proximity from his provider. Being aware of nearby information now, the recipient can request his provider to retrieve the whole content. Due to the tuple of the message ID the provider knows where the matching body is stored and indirectly transmits the content to the requesting user. 3.2 Indirect Addressing Indirect addressing betokens the assignment of location-based information to one or more publicly accessible user groups. The creator of a message is consequently unable to anticipate the identity or even the quantity of the recipients. Indirect addressing therefore enables users to widely spread information to a large audience, which imposes mechanisms to prevent unregulated penetration (spam!). Different from direct addressing where a provider model and a distribution mechanism of header information establishes a world-wide mobile location-based information service in an easy way, indirect addressing appears to be more complex. The propagation of header information does no longer seem to be applicable for messages that are addressed to different types of potential groups rather than to registered individuals, thus requiring a more elaborate concept for indirect addressing. Let us have a look at the groups: Basically, we distinguish global and local groups. • Global groups are applicable all over the planet. They are typically kept general (e.g., tourism, traffic, etc.) and are uniquely identified. For more flexibility global groups can be structured hierarchically. • Local groups are only valid within a restricted region. They are typically exclusive (e.g., students on a campus) but are also uniquely numbered. It is absolutely possible that different regions with different local groups overlap. The concept now works as follows: Every region is represented by an appropriate server (region server) the virtual regional boundaries of which are registered centrally, so that a region server can quickly be found due to its geographical extent. (This look-up mechanism operates similar to the well known domain name service DNS where IP addresses can be found due to a network name.) Providers – which continuously receive geo-positions from their connected clients – can consequently identify one or more region servers that cover the area a client is currently residing in. As clients are only connected to their providers the information about the local groups is indirectly passed to the clients via their providers (see Fig. 3). So, as the client moves around he is continuously kept informed about regional services and available local groups. Generally, it is not necessary to join a local group via a registration mechanism – everybody (neglecting special privileges for the time being) may automatically perceive the messages addressed to local groups. In this spirit, local groups are primarily used to logically structure information. Users are just required to filter the provided information they are interested in, which in a first simple attempt refers to the previously inflicted requirement where users may ask: “What kind of information is available here?” Global groups cannot be stored using the same mechanism as local groups do. A world-wide region server for global groups would have no boundaries and would
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have to serve every single connected client in the world. Instead, the local region servers provide information for global groups. They simply integrate selected global groups into their group hierarchy and declare thereby that information for global groups can be found at their covered area. This concept now satisfies the user request: “I am interested in …” meaning that a user just once declares his global interest (by selecting a global group) and automatically receives appropriate location-based messages from every region server which supports the selected global group. Users do not have to permanently check for a suitable group when crossing region borders. Having this concept of global and local groups, let us now examine the creation-, storage- and propagation mechanism for messages addressed to these groups: The appealing fact is that the mechanism for indirect addressing works very similar to the one for direct addressing, presuming that region servers can store information separated into a header and a body in the same way as providers do. Even the used data structures and storage models remain unchanged for indirect addressing.
Fig. 3. Region Server Concept
Fig. 4. Indirect Addressing Concept
Like in direct addressing, messages to local or global groups are stored at the provider of the creator. The message is separated into a header and a body with the difference that the recipient is no longer a single user but one or more local or global groups. Nevertheless, the recipient is a sequence of dot-separated numbers with a prefix denoting the destination server to which the header has to be transmitted no matter if this is a provider or a region server, thus letting the original mechanism for storing directly addressed messages also work for indirectly addressed ones (see Fig. 4). An approaching user of a different provider is indirectly informed via his provider about an active region server and the local and global groups available. A selection of one or more of these groups is forwarded to the region server which resends all appropriate message headers. Hereby, the provider itself does not store any data as Fig. 4 shows. Again, the prefix of the message id reveals the server holding the body.
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Fig. 5. Editorial Content on Region Server
The main purpose of a region server, however, is not to handle messages created by users of the system. As the succeeding section will show users should usually be hindered from creating indirectly addressed messages in order to prevent spam. Moreover, region servers should provide editorial content for its local and global groups for reading and execution. Therefore, messages are directly stored at the region server, without the need for propagating their headers. Message retrieval as shown in Fig. 2 remains unchanged (see Fig. 5).
4 User Interaction Regardless, what kind of visualization method is used for perceiving location-based messages (be it a two-dimensional geographical map, a simple list view or an augmented reality scene) the search and filtering interfaces are detached from these methods and can be applied equally. We suggest an interaction paradigm that reflects the two user requests initially stated: “I am interested in …” and “What kind of information is available here?” The first request can be handled by providing a selectable folding tree containing all global groups (see Fig. 6a). By default, nothing is selected in order not to confront the user with the load of globally addressed information. A selection within this tree enables users to automatically perceive the requested information type all over the world. Even when crossing region borders these settings guarantee the reception of equally grouped messages without requiring any further user interaction. Users are not supposed to pay attention when crossing region boundaries and to repetitively search for suitable topics of interest (groups) when entering a new region. With this mechanism users may e.g., express their interest in traffic messages, travel around and automatically receive all regional traffic messages no matter which local traffic management (region server) provides them.
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Fig. 6. a) “I am interested in …”, b) “What kind of information is available here?”
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The user selections within this tree are stored in the user’s profile at his provider, enabling him to keep his settings consistent even when changing devices. In the same way, the second request can be handled by providing an analogous selectable folding tree containing all currently available region servers and their (local and global) groups (see Fig. 6b). Global groups appear both in the first folding tree and in the second, with the difference that the second tree denotes all those groups that are actually available at the current location. The first tree always lists all global groups regardless if information for those groups is currently available or not. However, the selection mechanism is the same for both trees. These simple folding trees represent the interaction interface for users hiding the complex addressing concept presented in the previous sections and supporting them in finding or filtering the desired information.
5 Related Work Location-based services are emerging as the focal point of investigation for an increasing number of research labs and industry 3789101314172021: TagandScan 22 is a service for mobile phones that enables users to mark real physical locations with electronic tags. The tags contain a title, a description, the time and location when and where the tag was created. The position of the mobile phones is determined by triangulation of signal strengths within the GPRS network. The advantage of TagAndScan is based on the fact that the service works with conventional mobile phones without any additional hardware equipment. However, tracking is inaccurate. In cities tags can be positioned with an accuracy of about 100 meters whereas in rural areas a user has to consider several kilometers offset – too much for a detailed graphical representation. HotTown Geobots 12 is an approach of attaching context-aware services to objects or persons moving in a physical space. The software architecture provides locationbased information in a heterogeneous wireless network. The backbone of the architecture is a Geobot, a virtual representative of a physical object, which is aware of its current location and is additionally capable of serving information to other objects floating in a physical space. The Geobots do not exist as objects in the real world, instead they are modeled as software entities in a virtual world controlled by a location server. Users who physically enter this world (e.g. detected by GPS) must register at the location server and are consequently aware of where Geobots are located. The architecture enables parallel interaction in the physical and the virtual world. A new Geobot positioned in the virtual world immediately affects the real world because it becomes known to the users connected to the location server. Google Earth 7 provides location-based information and offers a rudimentary filtering mechanism for finding the desired information. However, this concept only considers global filtering attributes and does not refer to local peculiarities. All approaches have substantial similarity to the mobile location-based information service presented in this paper. However, our system offers a wide spectrum of features like extensibility, smartness, an elaborate plug-in mechanism enabling third
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party developers to dynamically throw in customer-dependent smart elements, and – most important – a scalable and world-wide applicable addressing concept, an attribute which cannot be found in any comparable communication service.
6 Future Work Due to the emerging field of location-based information services and the associated rising information mess and spam problem, addressing and filtering concepts inevitably gain in importance. Our future work primarily concentrates on a widespread user evaluation test in the first half of 2007 where numerous students will be granted access to this service on the university campus using notebooks, handhelds and cell phones in order to give us feedback concerning the usability of this service, especially the addressing concept. Furthermore, we plan to extend the addressing concept by contextual features. Groups (and the messages attached to these groups) may be conditionally restricted or extended, in order to prevent or grant access to messages. As an example, a group may be associated with the condition: “only for adults over 18 years”. Since the group is usually visible to every user, the providers (who are able to evaluate the attribute age) automatically prevent the contents to be transferred to the corresponding users.
7 Conclusion Now, that the technical basis for mobile location-based information services is established, concepts for higher level organizational issues have to be developed in order to successfully design accredited commercial applications. This paper has introduced one major higher level concept concerning addressing issues, meeting requirements such as scalability, global practicability, diminishing intrusiveness, handling distinctive user groups and employing access privileges. We have presented a flexible group system with local and global groups where users are able to automatically be member of or be incorporated via registration. We have shown the scalability of the addressing concept by outlining a provider and region server model with a header propagation mechanism as the key idea for distributing messages globally. And finally, we have given an idea of an interaction mechanism complying simplicity in finding or filtering information the users are interested in. This concept enriches mobile location-based services with great demand and high potential for the future indispensable in private and business fields.
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