Study And Implementation On Distributed Directory Service Based On CORBA

With the accelerated development of Internet and wide introduction of distributed computation, more and more distributed application systems, by means of the Internet, exchange, share and coordinate the information resource. And the primary problem is how to fulfill the information publishing and lookup. The directory service technology is born to be the key at this moment. In 1988, after series of development, ITU and ISO, the two biggest standardization organization, united together to draw up the current directory service of international standard. That is well-known X.500 series of protocol (ISO/IEC9594), which include: the model of directory service, abstract service definition, the process of distributed operation, protocol regulation, attribute type, object regulation, frame certification as well as the directory duplication mechanism etc. The widely accepted directory service standard is LDAP (Lightweight Directory Access Protocol), which inherits most of X500, particularly in description and frame of the directory service, but more flexible and easily extended in protocol design.This dissertation studies the system structure of the distributed directory service. To address the efficiency issue on resolution and operation of the large-scaled distributed directory service system, this research promotes shadow propagation and synchronized controlling system. And the work can be summaried from the followed aspects:1. The research prensents a new DSA (Directory System Agent) system frame, which follows to all the rules of Standard X500 and accretes shadow support;2. The research promotes directory shadow system. On the basis that most of the directory service operations are statistically directory resolution, we can use the shadow to efficiently control the network bandwidth consumption as a result of the distant directory resolution. Precise and perfect shadow synchronization strategy can insure the correctness of the information resolution.3. The research designs a directory resolution algorithm based on above directory Shadow system. By using this algorithm, the directory resolution operation and efficiency of service consumption can be greatly improved. Besides, by directory shadow system, it can insure successful resolution under the condition of forfeiture of node.4. The research designs a restored algorithm of directory node forfeiture, which can restore the data using Shadow system to improve the anti-destroyed ability of whole directory system.