Mobile devices, communication systems andapplications increasingly become more complex. In orderto manage mobile distributed applications a middlewareis essential which simplifies and speeds up the applicationdevelopment. A mobile environment with its heterogeneityand mobility has different requirements compared to afixed environment. Thus, new concepts and mechanismsfor a middleware have to be developed to cope with thechallenge of these heterogeneous distributed systems.In this article, we introduce a Web Service based middlewarefor mobile devices, adapted to a mobile environmentwith special focus on context-awareness. The contextawarenesswill be realized by a rule based data monitoringin order to minimize the communication frequency over themobile links and, thus, to minimize the runtime costs of themobile application. Within this middleware mobile contextproviders are able to publish their context-data. This datacan be remotely monitored by subscribing to a service ofthe context-provider and receiving notifications from thecontext provider.The Web Service based mobile middleware will be describedin general, special focus is given to the rule baseddata monitoring for context-aware applications. In additiona discussion of the expected application runtime costsregarding the communication is given.
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