Research On Concurrency Of Collaborative CAD System

As computer technique is widely used in engineering design field in recent years, CAD technique is developing faster and faster. Collaborative CAD system is a typical branch of CSCW. It supports a group of designers from different sites to accomplish the same design by cooperating and communicating freely with each other, which meets the modern pattern of information technology and has become a promising research. Nowadays, collaborative CAD systems are not perfect because of some limitations. Therefore, the concurrency control mechanism of collaborative CAD system is carefully studied in this paper.In order to maintain the consistency of the models of collaborative designs, locked mechanism is used to prevent concurrency conflicts considering most concurrency control in the recent collaborative feature modeling, thus limiting the concurrency granularity to a large extent. To improve the concurrency granularity of collaborative design, this paper deeply studies the concurrency control of collaborative design, including the following main activities:1. The characteristics of shared objects are analyzed and the concurrency conflicts in collaborative design are classified. Based on the analyses, a concept of Feature Dependency is put forward and based on it, a new definition of concurrency conflict for collaborative design is presented.2. The relationship of feature dependency of collaborative model is re-organized into a hierarchical graph. An efficient and based on feature dependency concurrency conflict detection algorithm is proposed. It introduces the algorithm in detail and also makes a detailed analysis. And according to the results of the corresponding conflict detection, a role-based conflict resolution methods and multi-version mechanisms are put forward. 3. Considering the weakness of role-based access control modes, an advanced mode ERBAC is introduced. The roles'permissions become more flexible by defining workgroups'permission, and ERBAC also supports multiple roles dynamically assigned, inherited roles, negative permissions and inherited permissions, especially adapted to large collaborative systems. And at the same time, it strengthens the security of collaborative systems by integrating authentication and data encrypted technology.4. A collaborative HUST-CAID proto-system is built and improved in this paper, with the strategy of concurrency control and access control mechanisms used in the system. After detailed introduction of the framework and functional modes of the collaborative system, it proves the proposed concurrency control mechanism to be effective, feasible and successful.