User defined prewrites for increasing concurrency in design databases

We introduce a prewrite operation before a write operation is performed on design databases, a database that consists of objects as engineering designs. A prewrite operation does not actually make a design but it only makes available the model of the design that the transaction will produce in future. Once the prewrite design by a transaction is announced, the transaction executes a pre-commit operation. After the pre-commit, read operations can access the prewrite design even before the pre-committed transaction has finally made the design and committed. Therefore, our algorithm increases the potential concurrency as compared to the algorithms that permit only read and write operations on the design objects. In our algorithm, a user explicitly makes available a prewrite model of the design to be finally produced. Similarly, a read transaction also mentions whether it wants to read a prewrite version or the final version of the design. Locking protocols using two phase locking are given to control concurrent operations