Web Services Integration Strategy with Minimum Hops Constraint in Wireless Sensor Networks

Both wireless sensor networks and service-oriented architectures (SOA) are very popular distributed computing paradigm. Web service is a widely accepted implementation of SOA. However, web service is based on Internet protocols and requires adaptation to suit the restrictions posed by WSNs. The development of Internet of Things has triggered research of web services of WSNs which made the consolidation of these technologies possible. At the same time, web service integration enables the support of more functionalities since many applications rely on not just one web service, but a whole school of them. Thus, how to compose and integrate different web services efficiently to provide complicated services becomes an essential topic. This paper investigates a problem which minimizes the number of hops of web services while integrating these web services to finish a set of tasks. We call this problem Minimum Hops of Service Integration Problem. It is proved that, when there are no precedence relationships between the tasks, the decision problem is NP-complete. This implies that this web services integration problem is NP-hard. For the case when the relationships between the tasks are in linear order, a polynomial-time, optimal web service integration algorithm, using greedy strategy, is provided. 1. Introduction Wireless sensor networks (WSNs) are used to monitor the concerned events through the collaboration between sensor nodes via wireless communication [1–3]. Recently WSN technologies have been recognized as one of the most important technologies that will seriously impact the world. Due to the advancement of the manufacturing technologies, especially on the communication and battery productions, tiny size of sensors can be equipped with the capabilities of sensing, wireless communication, and data processing. These types of sensors can not only sense and detect targets and changes in their environments but also process the collected data and transmit the data back to the data collection center or base station via wireless communication. The users can thus retrieve the status of the environments and develop interesting application accordingly. WSNs are to deploy massive amount of sensors in the sensing region to collect all kinds of environmental information and then pass the information via wireless network to the base station (sink) and then to the back-end user or manager via the Internet or satellites. WSN has gained much popularity because of the advanced development of microelectromechanical systems (MEMS) and its wide range of monitoring/tracking