This paper deals with the data model for multimesha objects. which is one of the crucial problems ofmultimexha database systems First. the characteristics of multimesha data are discussed. the existing multimedia data models are mmlyzed and the schema architecture of a multimesha database system Is presented. which is based on cncept and presentation modeling Secondly, a fonnal concept model for inulttmedia objects is defined Finally. the problem of spatio-temporal composition of multimedia objects is discussed. and a presentation model for multimedia objects is denfined.

The existing heterogeneous distributed database management systems (HDVBMSs) which are businss-oiiented will not be able to adequnte for many new and developing information processing applications. The important objective of these applications include the processing of complex objects and intelligence. Our approach is integrating logic and object paredigm to provide knowledge representation and infererence echanism in HDDBMS. This paper decribes the knowledge representetion in object-oriented heterogeneous distributed database system with semuntic association--OHDDB-DGI, presents the method of processing consltaints and rules in the global language OSAL which is Object-orientcd and of Semantic Association with bogic. and explains briefly the peculiarities of processjng inheritance and recursive inference.

安全策略模型是安全可信系统的基础。Bell-LaPadula模型是多级安全系统中广泛应用的安全策略模型，但它缺乏针对数据模型的完整性和一致性规则。以该模型为基础，针对数据库系统的数据模型，提出了一个以扩展客体层次结构为基础的安全策略模型。模型通过扩展客体层次结构使完整性成为模型的内在属性，并引入或重新定义了客体域、扩展安全公理和操作规则.模型更加适应多级安全数据库系统的要求，增强了策略模型与系统规格和高层模型的一致性。普遍性和通用性安全模型的扩展和增强，特别是安全性以外的特性的引入是安全策略模型向实际系统模型转化的必要步骤。

本文形式化地提出了一种适用于多媒体对象的概念模型OMCOM文中首先分析多了媒体数据模拟的特殊性，探讨了现有的多媒体数据模型的不足，从而提出了把多媒体数据模拟划分为慨念与表达两级模拟的思想概念级模拟多媒体对象的内容与结构；表达级模拟其表达，包括多媒体对象之间的时态关系和空间关系。OMCOM就是一种用于实现概念级模拟的模型。然后根据多媒体概念模拟的需求，形式化地定义了OMCOM的各个构成要素。最后根据OMCOM实例的格性质，建立了多媒体对象在概念级的运算体系——对象代数，形式化地定义了其中的各种运算以及对象代数表达式。

Currently, the popular DBMS products, for example Oracle、SQL Server、DB2、OpenBASE etc, offer highly efficient query function and complicated optimizing process. However in some circumstances, these successful DBMS query optimizer can not always make an optimal execution plan, even interfere performance. It is necessary to introduce the query hints as an query optimizing auxiliary measure. This paper analyzes the motivation and merit of the query hints, and the effection on the performance, finally describes the hints implementation in the OpenBASE