We propose a new transaction execution model in a mobile environment where a subset of data items is cached by each mobile host. This execution model allows each mobile host to execute transactions locally and, before their commits, to request certification from the database server on the wired network. The database server certifies a commit request only when the execution of its pertaining transaction was consistent. This protocol behaves like the optimistic concurrency control mechanisms in traditional transaction processing systems. However, traditional optimistic algorithms cannot be applied directly to mobile environments. We propose three strategies for validation of commit requests by the database server. These strategies aim to minimize both the processing overhead and transaction abort ratio. We compare the performance of the proposed strategies via both complexity analysis and simulation and suggest guidelines for choosing the best algorithm for different operating regions.