美國總統柯林頓在1997年七月一日發佈了『全球電子商業綱
要』，而同時德國國會也在同年七月四日通過了『資訊及通信服務
法』，這兩項舉世矚目的規範已宣告網路社會的到來。因此，若想在
開放式網路上達成安全且隱秘的電子資料交換，勢必要針對各種的
威脅加以考量。所以將目前的資訊電子化後，各公司機關之間透過
網路交換各種電子黃訊，如果要達到來源鑑別、存取控制、機密性、
真確性及存證等安全需求，必須運用密碼學的各種技巧來達成。
目前大部分將資訊電子化後的資料存放在資料庫系統中，而負
責建構資料庫安全模組的安全子系統將成為資料庫管理系統(DBMS)
的一部份，適合使用在許多階級組織普及的資料環境上的多層次安
全(Multi-Level Secure, MLS)關聯資料模組就是其中的一種模組，也
就是本論文討論的一個重點；在現行MLS模組中，詮釋所有可以看
見的元組涵義是很難達成，例如某些可見元組的涵義被正確地詮釋
是需要和其他元組做比較，而某些可見元組的涵義是模糊不清地被
詮釋著，因此，我們便在此論文中詳細描述一個使用者如何對了解
較低安全層級使用者對元組的詮釋。
一個完善的資訊存取控制系統，必須包含防範經由系統安全上
之漏洞而達成侵入事件的機制，這類防範機制是用電腦稽核的方式
來對整個資訊系統與安全有關的事件做記錄、檢查與分析。而在論
文中我們加入了使用兩個時間維度的觀念用在稽核機制上，使整個
安全機制系統除了補足存取控制機制所無法達成的任務外，更使得
整個稽核機制更顯得完整。

Access control policies state if, and how, system subjects and objects can be grouped, in order to share access modes according to given authorizations and rules. Moreover, the policies state if, and how, access right can be transferred. This paper studies various access control policies, and application on public key infrastructure.
Membership is implemented by default in various systems to simplify design and enforcement problems. Classification in hierarchical levels (totally or partially ordered) for groups of subjects and groups of objects is a widespread procedure; access controls map into controls of information flow among the different levels. This procedure is largely used in multilevel security systems for military environments, where access control policies are essentially control policies for information flow.
Multilevel relations, based on the current multilevel security (MLS) relational data models, can present a user with information that is difficult to interpret and may display an inconsistent outlook about the views of other users. Such ambiguity is due to the lack of a comprehensive method for asserting and interpreting beliefs about lower level information. In this paper we identify different beliefs that can be held by higher level users about lower level information, and we introduce various concept of interpreting beliefs.
And we introduce finally audit machine. Auditing is useful deterrent tools for data physical integrity, as well as for subsequent analysis of access sequences to a database.