| Database is an important part of CBTC system and act as a key point in the CBTC system secure operation. As dynamic data that describing line condition change frequently, so frequent maintenance operations are needed as to keep the real time character and correctness of data in the database. Thus, every subsystem can get real-time, efficient, secure and reliable data information from database. Database is a safety equipment in CBTC system. It is key problem in designing database and maintenance system that how to actualize database maintenance and how to ensure safety and reliability of data in the course of database maintenance.This paper is supported by the science and technology program of Beijing-studying and developing the system of communication based train control, thoroughly lucubrate the database maintenance system of CBTC system. This paper adopts real-time maintenance strategy which can ensure the data information is up to date when subsystems of CBTC system query and download data information from database.After analyzing and comparing the advantages and disadvantages of existing database architectures, multilevel secure database architecture based trusted subject architecture has been proposed. Then this paper analyzes the characteristic of access control in this architecture. Base on the multilevel secure database architecture, the emphases of this paper is to study thoroughly database maintenance mechanism. Special authority is assigned to maintenance administrators. Signing and identifying mechanism prevents that maintenance administrator's non-authorizing operation. Audit mechanism provides evidence for finding out system responsibility and reproducing maintenance operation, ensures database maintenance security on the other hand. |
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