SQL Server数据库是当今信息管理系统中有代表性的大型网络数据库之一。文中讨论在SQL Server 2008中通过触发器技术实现数据完整性的机制,介绍触发器的概念、分类,重点论述DML触发器的实现过程,结合具体实例,设计DML触发器监督财务人员对资金的各种业务操作,包括插入、删除和更新记录,分析了触发器设计的基本步骤,并改进触发器设计,使审计表能够记录全部变化的数据,从而反映了触发器的应用在提高系统性能、维护数据库完整性、有效性等方面的强大功能。
Property path is the latest navigational extension of the standard query language SPARQL 1.1 for the Semantic Web.However,in the existing SPARQL query systems which support property path,the query efficiency is very low and does not support reasoning.This paper proposes a new existential semantics which has polynomial-time evaluation complexity and an equivalent relationship with the current semantics,and transforms the property path expressions to the extended nested regular expressions based on the existential semantics and proves the semantic equivalence after the transformation considering the RDFS semantics.The property path query engine is achieved by implementing the nested regular expressions algorithm and the transformation rules from the property path expressions to the nested regular expressions,which maintains the syntax simplicity of property path and the goal-oriented polynomial-time reasoning to avoid computing the RDF graph closure.The experiment results not only show the characteristics of query engine based on the existential semantics in efficiency and reasoning,but also further validate the equivalence between the results based on current semantics and those based on the existential semantics for property path after the removal of duplicate values.
