In this thesis, We propose new validation schemes, COREV and R²COREV, for scheduling transactions optimistically in client-server based mobile database systems. In the mobile database systems environment, validation throughput could be seriously degraded due to waiting time in validation process resulting from various delay factors in data transfer through wireless channels. Unlike the previous approaches, our schemes remove the waiting time by rearranging commit order of transactions. R²COREV is devised to reduce about ratio by rearranging the serializable order of them. For preserving serializability corresponding to the substantial execution order, which could be perverted easily in mobile environments, we devised a new scheme for assigning transaction number, called serial-order restoration scheme for transaction numbering (SORT). It enables transactions to be executed in a serializable order and validated without any waiting time.