Research On The Basic Platform For Replicated Collaborative CAD System

The development of computer network, grid computing, concurrent engineering and CAD/CAM technologies not only changes dramatically the model of production process, but also accelerates the demand and application of internet product design. This paper systematically presents theories and technologies related to the basic platform and propose a solution to the real-time designing of product.This dissertation starts with the background of the research about Collaborative CAD, and presents in details about the key technologies about the fundamental platform—concepts ,futures and the current situation around the world about data exchange,concurrency control,access control and late join mechanism. This is also the basis of the dissertation.Based on the research of real-time modeling, this dissertation also constructs the replicated Collaborative CAD network topology and its functional frame. In order to support Collaborative design, we did some special operations and optimizations about CAD platform, supporting environment of Data communication and multimedia communication. This research work provides theory support and evidence for how to build a Collaborative CAD System.Data exchanging is used to ensure the efficiency and user experience of the whole collaborative system. An implicit feature representation data exchange model is proposed based on a deep research about the virtues of data exchanging for replicated collaborative CAD system. In essence, instead of exchanging geometry and topology information, only parametric information of features is exchanged, and geometry and topology information are left to evaluate by CAD system internal environment. To accommodate Collaborative real-time modeling, object-oriented serializable class message encapsulation,semantic feature re-construction and geometric matching based on dynamic octree technology are used to make the internet transmit more efficient, and implicit model exchange based on features is implemented. This method is proved to be efficiency on improving the performance of Internet and enhancing the quality in real-time.Concurrency control is used to constrain users'operations and rule the time schedule of designing. A multi-level distributed concurrency control model is proposed for replicated collaborative CAD system based on understanding the effect of the complicated relationships among CAD features (e.g. dependent relationship, geometrical relationship) to the confliction of collaborative operations. Using feature as its basic control unit, this concurrency control mechanism settles four progressive confliction detect rules, including collaborative operations rules, collaborative logic rules, collaborative dependence rules and collaborative concept rules. It also constructs a self-compatible, conflict-meditation and third-lateral-judge multi-layer confliction mediation mechanism based on the distributed mutual exclusion algorithm, and the multi-level distributed concurrency control is implemented. This method is proved to be efficiency and feasibility on controlling collaborative operations.Access control is used to ensure the confidentiality and integrity of the collaborative design data. A multi-grained and dynamic security access control (MGDAC) model is proposed based on understanding about the characteristics of the CAD model hierarchy and role-based delegation for replicated collaborative CAD system. A multi-grained quantified privilege model is developed to simplify the process of permission assignment and calculation for enriching the expression ability and helping to realize fine-grained access control. The dependent relation of permission and the permission state migration are brought into MGDAC for dynamic authorization management based on the basic theory of workflow. The delegation attribute expression and delegation trustworthiness are brought into MGDAC for delegatee's qualification filtrating. Three types of delegation constraints are further studied and analyzed, including temporal, globalization and obligation. Using these constraints, delegation condition and constrained usage is described. Based on the practice, MGDAC model is more efficient to control collaborative operations. It meets the characters of design tasks, i.e. separate working ability, dependency and interactivity.Late join mechanism is used to keep the latecomers consistent with current working process. A distributed late join algorithm with fault-tolerance based on three multicast group (T-MDLJ) is proposed for replicated collaborative CAD system. The latecomers joining mechanism has been analyzed and key issues of late join algorithms are discussed in detail. The simulation test shows that the T-MDLJ algorithm reduces the initialization delay, network and application load efficiently. To the problem of digital support for internet-based collaborative design, Prototype system of Replicated Collaborative CAD System is designed, and CAD is implemented in network.