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In mobile real-time database systems, the objects of concurrency control should take saving system resources and supporting disconnection into consideration, besides ensuring database consistency, reducing the number of expired transactions and avoiding "priority inversion". In the paper, a nested transaction model for mobile real-time transactions is discussed. Then a divergence control lock model based on prudent ordered sharing and a check-out/check-in protocol supporting disconnections are given. DC/POS-PAI-2PL is a two-phase lock strategy integrating these methods for mobile real-time transactions. The performances of DC/POS-PAI-2PL are analyzed in the end. It is shown that the suggested transaction model and DC/POS-PAI-2PL can improve system performances.