Concurrency control strategies for web-based collaborative assembly system

In this paper, the concurrency conflicts of collaborative assembly for complex products in the Web environment are studied. Five types of concurrency assembly conflicts are summarized according to the operation commands in the collaborative assembly process, which are the inconsistent results produced by multi-clients, multiclients grasping the wrong parts simultaneously, multi-clients assembling the same parts or subassembly in parallel, feasible concurrent subassembly operations being prevented and conflicts of assembly constraints in collaborative assembly process. A Hierarchical Hybrid Concurrency Conflicts Control Model is proposed firstly, which is composed of two control layers with four kinds of concurrency control strategies. The concurrency control strategy based on global assembly sequence of the upper control layer is to deliver the exact sequences from server to collaborating clients for checking the correctness of assembly operation and the two former concurrency conflicts are eliminated effectively. The rest three concurrency conflicts are resolved by the serialization strategy of assembly operations, serverlocked and client-unlocked strategy and strategy of designing assembly constraints library respectively which are integrated in the lower control layer. Finally, the concurrency control strategies are applied in a virtual collaborative assembly system (VCAS) and their validity and effectiveness are proved.. Copyright