Location based Services in Mobile Environments

Location-based services (LBS) are services that utilize their ability of locationawareness to simplify user interactions and adapt to the specific context. With advances in automatic position sensing and wireless connectivity, the application range of mobile LBS is rapidly developing, particularly in the field of geographic, telematic, touristic, and logistic information systems. However, present LBS are to a large extent incompatible with each other and unable to interoperate on location semantics. They are mostly bound to a specific technology reflecting the preferences of the service provider. Typically, proprietary protocols and interfaces are employed to aggregate the different system components for positioning, networking, content, or payment services. In many cases, these components are glued together to form a monolithic and inflexible system. If such a system has to be adapted to another technology, e.g., the change from GPS positioning to inhouse WLAN or Bluetooth positioning, it has to be entirely reengineered. Due to the dynamic nature of mobile environments, available resources as well as achievable quality of service levels are incessantly changing. Thus, adaptivity – the ability of steady interoperation of variable resources under changeable connection conditions – becomes crucial for service end-to-end availability in mobile environments.
Let us consider a position sensing service, for example, a satellite-based GPS. If a mobile device moves from outdoor to indoor environments, the signal will likely become unavailable and position sensing will fail. Without the location information expected from this subservice, composite services depending on it will become unavailable as well. To arrive at seamless operation, on-the-fly switchover to an alternative position sensing service using a different technology is required. To choose from multiple possible position sensing services, the decision has to consider service availability, quality of service properties, and costs. In the near future, most mobile and wearable devices are expected to have multiple position sensing technologies at disposal, e.g., GPS, GSM, WLAN, and Bluetooth. Nevertheless, new technologies, like at present WiMax or RFID, are continuously emerging. Thus hardware devices and software components, their interfaces and architecture have to be able to deal with changing conditions to make mobile location-based services highly available.
We show how to use Web Services standards for propagation, discovery, and composition of location-based services in mobile environments. To achieve semantic interoperability we express location information in XML using context-specific ontologies. The achieved interoperability allows for context- aware on-demand service composition making the composite service highly available and resilient to environmental dynamics and uncertainties.

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