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So sánh Dựa Hỗ trợ cho tính năng bổ sung CORBA Các CORBA Dịch vụ an ninh hỗ trợ việc xác định, xác thực, uỷ quyền, và kiểm soát truy cập của các nguyên tắc. Nó cũng cung cấp cho kiểm toán bảo mật. Phân phối thu gom rác thải không phải là quy định. | COMPARISON OF THE THREE PARADIGMS 145 Table 4.4 Comparison Based on Support for Additional Features RMI CORBA DCOM Enforces the creation of a RMISecurityManager object. This ensures that downloaded class code for any object passed to the client does not access the system resources. Distributed garbage collection is handled by the Java virtual machine. The CORBA Security Service supports the identification authentication authorization and access control of the principles. It also provides security auditing. Distributed garbage collection is not specified. Asynchronous call-back routines are supported where in a server can call back a method on any of its clients. Deferred synchronous calls allow clients to poll on a delayed response from the server. Event service allows consumers to either request events or be notified of events. DCOM supports robust security by allowing users to specify userlevel authentication and access-level rights through access control list over objects. Distributed garbage collection is activated by a pinging mechanism by which the server object detects whether clients are connected. Call-back interfaces are supported in DCOM. TABLE 4.5 Comparison Based on Performance Experiment Parameter Passing RMI ms CORBA ms DCOM ms Ping By value 25.792 163.823 135.545 Matrix-by-vector By reference 6781.155 1546.716 123 305.330 multiplication part of the overhead. Second the DCOM implementation uses the concept of moniker for obtaining object reference. This is achieved by converting the moniker into a string and writing the string into a moniker file which could later be read by the client program to obtain the reference. In the case of matrix-by-vector multiplication the client passes the matrix and vector objects by references to the central server. The central server then looks up the available processor objects by reading the moniker file corresponding to the processor object and then performs the computation. This reading of the moniker file is an I