Currently, the context management solutions for the Internet of Things are the subject of numerous studies which are achieved through the expansion of the context manager for ambient environments. In literature, there are different approaches enabling the context management for internet of things (IoT). This paper studies these approaches, which are well known according to our defined criteria such as heterogeneity, mobility, the influence of the physical world, scalability, security, privacy, quality of context, autonomous deployment of entities, characterization multi scales, and interoperability.

• This paper describes an algorithm for reformulation of XQuery queries. The mediation is based on an essential component called mediator. The main role of the mediator is to reformulate a user query, written in terms of global schema, in queries written in terms of sources schemas. Our algorithm is based on the principle of logical equivalence, simple and complex unification, to obtain a better reformulation. It takes as parameter the query XQuery, the global schema (written in XMLSchema), mappings GLAV and gives as a result a query written in terms of sources schemas. The results of implementation show the proper functioning of the algorithm.
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