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Top1. Introduction
The ubiquitous computing Mark Weiser (Weiser, 1991) main objective is to incorporate technology into the user’s environment by making it so easy to use that it would become invisible to users. They will be able to focus on their goals instead of thinking on the tools the environment offers. This ubiquitous computing world, as dreamt by Mark Weiser, is now becoming a reality with the increasing on the amount of devices and information available everywhere. People is more and more habituated to receive information according to their location and preferences (Garlan, Siewiorek, Smailagic, & Steenkiste, 2002). Service- Oriented Architecture (SOA) has been widely applied for integrating devices, sensors, actuators and software applications (Web Services for Devices Initiative, n.d.; Timmermann & Golatowski, 2011). State of the art service discovery approaches in pervasive environments use techniques from the traditional SOA field, where explicit user requests are the driving factors of service discovery.
In pervasive environments, user context and user preferences become essential aspects when deciding, which of the available services are of most interest to the user in a given situation.
The user context is rich and ever-changing; it covers aspects such as user location, current time and environmental information. These continuously changing aspects pose a significant challenge to state of the art discovery mechanisms (Zhu, Mutka, & Ni, 2005). We argue that most service discovery requests in pervasive environments are implicit. The system should discover and select services in response to changes in the user context (Rasch K. et al. 2011), even if the user did not issue an explicit service discovery request to the system.
Web Services for Devices (Web Services for Devices Initiative, n.d.) specially aim at permitting interoperability, since they do not rely on any specific programming language or hardware architecture (Ferry, Hourdin, Lavirotte, Rey, Riveill, & Tigli, n.d.). Service for Devices also suffers constraints related to devices’ resource dependencies: frequent disconnections, memory limitation, narrow network bandwidth, limited power, processing capacities, etc. Therefore, the description of Service for Device must include these limitations to inform of specific constraints associated to the provided service.
To go further, more specific works on the description of ontological devices and services such as are thus necessary to give a complete Service for Device description. We use SWRL (Semantic Web Rule Language); it can express Horn-Logic Rules, which the OWL cannot express because it is based on DL (Description-Logic). So, we can offer inference service to users, with a wide range of expressions.
Devices being most often connected to the real environment of applications, associated services need to offer mechanisms which take into account applications’ proactivity to environmental variations. Web services for devices thus define communication protocols using events (subscription, notification) in an asynchronous execution context and include concepts of services and event frameworks, as well as decentralized and dynamic discovery.