SmoS: A Scalable Mobility Server

Mobile information systems are often distinguished as traditional information systems with additional support for mobile devices. This idea is based on the mostly used cellular network architecture. Mobile units have to be wirelessly connected via a base station to a server integrated in a fixed network if their users want to use the capabilities of the information system which are provided by this server. Due to the increasing distribution and use of small footprinted hardware like mobile phones or PDAs such solutions have to consider a new requirement, the great number of involved mobile units. In this contribution we present SMoS, a scalable mobility server, we are currently developing. Our approach to handle a great number of clients is based on the subsumption of semantically related data to logical fragments which are computed on an integrated global view over heterogeneous data sources. Mobile database clients replicate data via this mobility server (MS). Therefore, they register queries on the server. These queries are used for sending the current answer and upcoming updates to the according mobile clients. Furthermore, context information1 like location of the mobile device or time are used for the annotation of the fragments. A new query that uses a known context can be executed on fragments according to this context. We assume that mobile clients can be uniquely identified. So the server stores the queries (including the context), that reflect the area of interests of the users of the mobile clients, and the IDs of the clients which have performed these queries already. That means, for each mobile client the partially replicated fragments are known. So, updates and inserts which are performed on the database server by the data sources as well as by the mobile clients have to be propagated only to mobile clients that queried semantically related data before. These characteristics have to be reflected in every step of the replication process [?]. Thus, the following three challenges for a mobility server appear: