244 7 Navigation AT: Context-aware Computing

In order to make accurate inferences regarding a user’s context, acquired contextual information will need to be effectively interpreted, consolidated and managed. This particular aspect of design is termed middleware design, which aims to provide toolkits and services to facilitate the discovery and delivery of context data in an efficient manner. Dey and Abowd (2000b), for instance, developed a component-based framework, called the Context Toolkit, which is centred on three main abstractions. First, ‘context widgets’ wrap around underlying sensors and deliver information to interested components/services, such as a change in GPS location delivered to an application that works out the user’s distance from their destination. Second, ‘context aggregators’ store low-level logically related sensed data (such as a person or location) for relevant application entities, and, third, ‘context interpreters’ are responsible for abstracting low-level data to higher-level information. Some of the technological issues associated to this challenging area of research and development, will be discussed in Section 7.4.5.

7.4.3 Capabilities of Context-awareness

The capabilities of a context-aware system are dependent on both the technologies of the system itself, and the dissemination of, and level of communication with, other computers within a ubiquitous computing environment. For instance, a greater density and variety of computers embedded within everyday objects may result in (i) a greater exchange of contextual information, (ii) a greater awareness of the environment, and (iii) a more robust level of service for the user. Four categories of context-aware capabilities are described below (Pascoe 1998):

•Contextual sensing. Application senses environmental states and presents them to the user. For instance, a GPS receiver takes in a location, compares it to a digital map, and then informs the user of their location.

•Contextual adaptation. Application leverages contextual knowledge by adapting its behaviour to integrate more seamlessly with the user’s environment. The application, for instance, could automatically re-route a visually impaired traveller to avert hazardous excavation work on a pavement.

•Contextual resource discovery. Application discovers other resources within the same context as itself and exploits these resources while the user remains in the same context. For instance, when people travel abroad, local mobile phone networks often send text messages to inform people of where they can find useful information about the immediate environment. A context-aware device could automatically acquire this information on behalf of the user, such as downloading train timetables.

•Contextual augmentation. Application allows the user to augment the environment with information at a specific location for other users. For instance, a visually impaired traveller could leave a location-specific electronic message about a hazard. Other visually impaired travellers would only receive this message if the same location were visited.

As mentioned earlier, existing GPS-based systems for visually impaired people offer limited contextual detail since most are based only upon contextual sensing. Context-aware computing could therefore extends the visually impaired person’s spatial awareness and knowledge, and provides more support, flexibility and opportunities for independent mobility involving a wide-range of activities.

7.4.4 Application of Context-aware Principles

The purpose of this section is to illustrate, using three case studies, the application of context-awareness in research and development. Currently, only one prototype that explicitly draws upon context-awareness has been developed to assist the distant navigation requirements of visually impaired people. For this reason, we will describe two other prototypes, namely, a context-aware mobile tourist guide, and a location messaging system.

Case study 7.1: The Drishti System

The Drishti wireless navigation system, which is being developed by researchers at University of Florida, transmits route information to visually impaired and disabled people in order to assist navigation through dynamic outdoor environments (Helal et al. 2001). Drishti is designed to generate optimised routes based upon user preferences, temporal constraints such as traffic congestion, and dynamic obstacles such as ongoing ground work, e.g. routes involving fewer hazards may be chosen over the shortest route. Re-routing is supported if unexpected events occur, and travellers can also add notes about certain conditions or problems encountered as a reminder if the route is revisited (such as a pothole on the road).

Drishti integrates several hardware components including a wearable computer, an integrated GPS/Beacon/Satellite receiver, an electronic compass, and components for various wireless networks. Software components include a spatial database called ArcSDE to manage GIS datasets; a route store called NetEngine to define, traverse and analyse complex geographic networks; and a mapserver called ArcIMS to serve the GIS datasets over the Internet. Communication between the user and interface is accomplished using ViaVoice which transmits detailed explanatory cues using text-speech software and also executes verbal commands of the user using voice recognition.

While the Drishti system provides many useful levels of functionality, the system is limited to outdoor environments and was tested using a very precise task and scenario, i.e. through a university campus. Testing this system in more contexts, such as indoor, and for other mobile tasks and visually impaired user groups would be more challenging and would involve acquiring far more contextual information; a technological issue discussed in Section 7.4.5. Other capabilities of contextawareness could also be explored such as allowing visually impaired travellers to disseminate notes to others, e.g. warning others of potholes in the environment. This capability is discussed in case study 7.3.

by people from different demographic and cultural backgrounds. Tourists visiting a city would have contrasting expectations of supported activities, levels of functionality, and methods of user-interface interaction. The versatility of the system is also critical, as there are likely to be (i) vast differences in how tourists would wish to experience a city, and (ii) situations where tourists make unpredictable/incidental decisions regarding future activities. Additionally, the tourist’s dependency on the system would need to be measured against actual city experience.

Case study 7.3: Location messaging systems

Both previous case studies concern systems that transmit localised and personalised information to the user, either prior to a tour/journey, or as a route is experienced. The third case study, however, describes a system which is centred on an entirely different capability of context-aware computing; that of contextual augmentation (described in Section 7.4.3).

The stick-e document, described by Brown (1996), is a framework for representing this capability in the design of a wide variety of context-aware applications. It is described how the user, who would possess a location-aware mobile device, can leave stick-e notes (which are the electronic equivalent of a Post-It™ note) at specific locations in space. When the user revisits this location, the message is triggered and displayed to the user. These notes can also be broadcast and exchanged to a wider audience, if this is considered to be a desirable design feature. In this example only the location is used to determine when a note is triggered, though Brown also describes how other elements of context can be included to make the presentation of notes more useful. Triggering events could be dependent on (i) the adjacency of other objects or people, e.g. when the user is in the presence of a particular friend, (ii) critical states, such as temperature thresholds, and (iii) time ranges, e.g. only display a note about a tourist attraction during opening hours.

The exchange of notes between users would not normally be done singularly, i.e. one note at a time; rather, a stick-e document would be exchanged containing a group of notes that have a logical relationship, such as notes relating to a particular activity or tourist trail. The dissemination of documents could be (i) downloaded to the mobile device using the Internet, (ii) exchanged between two devices using beaming, such as Bluetooth, or (iii) loaded into the mobile device via a wireless link (in this method, notes within the document could be updated regularly in order to reflect environmental change).

The stick-e document would have obvious benefits for communities of visually impaired people, who could share experiences about different situations and environments, e.g. alerting others of hazards. The management, dissemination, and presentation of documents and notes are critical technological, human and social issues. Large amounts of notes would need to be managed, some of which may be irrelevant, inappropriate, or out of date. Adequate controls would need to be put in place in order to ensure notes are not displayed repeatedly if the user decides to revisit a location for the second or third time. Much of the triggering states may have to be customised by the user, requiring considerable time and knowledge of how the system is likely to respond. Lastly, sharing notes with others has the potential to get obtrusive and tedious, especially where there are conflicts of interest.