多级安全数据库管理系统查询处理器的设计

多级安全数据库与传统的数据库最大的不同就在于它引入了安全级的概念，访问数据库的主体和数据库中的客体都被赋予了安全级，主体对客体的访问遵循强制存取控制规则．多级安全查询处理器是多级安全数据库的核心部分，它提供对安全级查询的支持．多级安全查询处理器必须保证用户的查询不违反数据库系统安全性的要求．分析了多级安全查询处理的执行过程，定义了多级安全查询语言的语法，利用编译器生成工具Yacc设计了一个多级安全查询处理器，并对其进行了分析．

Design of multilevel secure query-processor

The main difference between multilevel secure database and conventional relational database is that the former brings the concept of security level. Subjects accessing the database and objects stored in the database are assigned security labels. Accessing of subjects to objects obeys the mandatory access control rule. Multilevel secure query processor is the core component of multilevel secure database. It supports querying by security level and must ensure that user's querying will not violate the security requirements of database. This paper analyzes the process of multilevel secure query processing, defines the syntax of the multilevel secure query language, designs and analyzes a multilevel secure query processor by Yacc-a complier generator.