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INTRODUCTIONHowtoprotectthedatabase ,thekernelre sourcesofinformationwarfare,isbecomingmoreandmoreimportantsincetherapiddevelopmentofcomputerandcommunicationtechnology .TheArtificialIntelligenceInstituteofZhejiangUni versityhasprototypedaDatabaseSecuritya… 相似文献
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This paper presents an efficient way to preserve the volume of implicit surfaces generated by skeletons. Recursive subdivision is used to efficiently calculate the volume. The criterion for subdivision is obtained by using the property of density functions and treating different types of skeletons respectively to get accurate minimum and maximum distances from a cube to a skeleton. Compared with the criterion generated by other ways such as using traditional Interval Analysis, Affine Arithmetic, or Lipschitz condition, our approach is much better both in speed and accuracy. 相似文献
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INTRODUCTIONTheOSSI(OffsetSurface/SurfaceIntersection)problemisasub-problemofgeneralSSI.AlthoughtheOSSIproblemcanberesolvedbyapplyinggeneralSSIalgorithm,itiscomputationallyexpensiveandexhaustive.Inrecentdecades,effortshavebeenfocusedoncomputingSSIexactly,efficiently,androbustlyinageneralsetting(Abdel-MalekandYeh,1997;Changetal.,1994;BurkeandSabharwal,1996;Mullenheim,1991).Thesetechniquescanbeclassifiedmainlyintofivecategories:algebraic,latticeevaluation,marching(tracing)method,… 相似文献
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INTRODUCTION Computer Supported Collaborative Work(CSCW) refers to technologies that use computertechnologies, multimedia technologies and networkcommunication technologies to support geogra-phically distributed users to collaborate with designtasks under shared environments. It is argued thatthe product development period may be shortenedgreatly when users independently and collabora-tively join in the designing, planning and assemblyprocess with the same product under a distributedenv… 相似文献
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Conventional methods for solving intersections between two offset parametric surfaces often include iteratively using computationally
expensive SSI (surface/surface intersections) algorithm. In addition, these methods ignore the relations between the intersection
curves of parametric surfaces with different offset distances. The algorithm presented in this paper, makes full use of the
topological relations between different intersection loops and calculates intersection loops with the help of previously calculated
intersection loops. It first pre-processes two parametric surfaces to obtain the characteristic points, called topology transition
points (TTPs), which can help in the subsequent finding of the topologies of the intersection curves. Then these points are
categorized into several distinct groups, and we can determine the calculation strategy for searching initial points by analyzing
the properties of these TTPs on the surfaces. Hence, all intersection curves can be marched from initial points by the tracing
algorithm. The proposed algorithm could calculate intersection curves robustly and effectively, and has been tested to be
capable of overcoming the degenerate conditions such as loop and singularities leaking that occur frequently in conventional
algorithms.
Project supported by the National Research Foundation for the Doctoral Program (No. 2000033554) of Higher Education of China
and the Natural Science Foundation of Zhejiang Province, China (No. 6001107) 相似文献
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This paper applies genetic simulated annealing algorithm (SAGA) to solving geometric constraint problems. This method makes
full use of the advantages of SAGA and can handle under-/over-constraint problems naturally. It has advantages (due to its
not being sensitive to the initial values) over the Newton-Raphson method, and its yielding of multiple solutions, is an advantage
over other optimal methods for multisolution constraint system. Our experiments have proved the robustness and efficiency
of this method.
Project (No. 6001107) supported by the National Science Foundation of Zhejiang Province 相似文献
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Constraint is an important aspect of role-based access control and is sometimes argued to be the principal motivation for role-based access control (RBAC). But so far few authors have discussed consistency maintenance for constraint in RBAC model. Based on researches of constraints among roles and types of inconsistency among constraints, this paper introduces corresponding formal rules, rule-based reasoning and corresponding methods to detect, avoid and resolve these inconsistencies. Finally, the paper introduces briefly the application of consistency maintenance in ZD-PDM, an enterprise-oriented product data management (PDM) system. 相似文献
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INTRODUCTION Image segmentation plays an essential role in jacquard image analysis. A jacquard image consists of many complex patterns which contain detailed, in- tricate topological curves. An accurate extraction of pattern features from jacquard images promises reli- ability for jacquard fabric CAD. Although, many algorithms have been proposed for the segmentation problem, they have difficulty in capturing the com- plex structure of the visual features, such as complex contours of a ja… 相似文献
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Database Security and Protection System (DSPS) is a security platform for fighting malicious DBMS. The security and performance
are critical to DSPS. The authors suggested a key management scheme by combining the server group structure to improve availability
and the key distribution structure needed by proactive security. This paper detailed the implementation of proactive security
in DSPS. After thorough performance analysis, the authors concluded that the performance difference between the replicated
mechanism and proactive mechanism becomes smaller and smaller with increasing number of concurrent connections; and that proactive
security is very useful and practical for large, critical applications.
Project (No. 45.6.1-017) supported by the National Defense Pre-Research Fund of China 相似文献
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This paper presents a novel Web Service based distributed collaborative CAD system employing feature as its collaborative design element and uses XML to define feature operations and communication protocol between the server and the client. To reduce network load and increase response ability of the system, the feature information is updated incrementally on the client. The system supports collaborative designing on heterogeneous platforms. Its framework and communication protocols are analyzed in detail. The experimental results from the developed prototype system showed that it can effectively support collaborative design under the distributed environment. 相似文献