SQL Server2000数据库实时备份

数据库备份是数据库安全的重要保证。但是,采用一般的数据库备份一旦数据库被破坏,上次数据库备份后对数据库进行的增删改数据均无法恢复。以SQL Server2000为平台,从应用实践角度提出SQL Server2000数据库实时备份的方案,主要讨论服务器端数据库实时备份,分析它的并发性、安全性、可靠性和动态切换,以及对应用程序透明。     

Technology for testing nondeterministic client/server database applications

The execution of a client/server application involving database access requires a sequence of database transaction events (or, T-events), called a transaction sequence (or, T-sequence). A client/server database application may have nondeterministic behavior in that multiple executions thereof with the same input may produce different T-sequences. We present a framework for testing all possible T-sequences of a client/server database application. We first show how to define a T-sequence in order to provide sufficient information to detect race conditions between T-events. Second, we design algorithms to change the outcomes of race conditions in order to derive race variants, which are prefixes of other T-sequences. Third, we develop a prefix-based replay technique for race variants derived from T-sequences. We prove that our framework can derive all the possible T-sequences in cases where every execution of the application terminates. A formal proof and an analysis of the proposed framework are given. We describe a prototype implementation of the framework and present experimental results obtained from it.     

分布式数据库服务器的可信性研究

主要介绍了分布式数据库服务器系统中的可信研究,并讨论了其中有关可信授权的实现、权限的管理逻辑以及授权机的具体运行过程,给出了可信分布式数据库服务器系统的模型。系统中采用了信任链机制、基于角色的访问控制模型、两级日志、可信认证等技术,同时给出了可信在分布式计算机系统中的实现技术和途径。     

Strategic agents for multi-resource negotiation

In electronic commerce markets where selfish agents behave individually, agents often have to acquire multiple resources in order to accomplish a high level task with each resource acquisition requiring negotiations with multiple resource providers. Thus, it is crucial to efficiently coordinate these interrelated negotiations. This paper presents the design and implementation of agents that concurrently negotiate with other entities for acquiring multiple resources. Negotiation agents in this paper are designed to adjust (1) the number of tentative agreements for each resource and (2) the amount of concession they are willing to make in response to changing market conditions and negotiation situations. In our approach, agents utilize a time-dependent negotiation strategy in which the reserve price of each resource is dynamically determined by (1) the likelihood that negotiation will not be successfully completed (conflict probability), (2) the expected agreement price of the resource, and (3) the expected number of final agreements. The negotiation deadline of each resource is determined by its relative scarcity. Agents are permitted to decommit from agreements by paying a time-dependent penalty, and a buyer can make more than one tentative agreement for each resource. The maximum number of tentative agreements for each resource made by an agent is constrained by the market situation. Experimental results show that our negotiation strategy achieved significantly more utilities than simpler strategies.     

SQL Server数据库应用程序中数据库安全性研究

为了实现SQL Server数据库应用程序中数据库的安全性,从SQL Server数据库自身的安全访问机制、SQL Server数据库视图、存储过程、应用程序角色及应用程序服务器连接到Internet网络上实现数据库安全性进行分析,说明了SQL Server数据库应用程序中数据库安全管理策略.     

基于Webaccess平台的SQL server数据库的应用

介绍了采用SQL数据库,分别在Webaccess脚本、VB采集程序和Delphi的检测程序中调用,解决大量数据的流通及存储的问题.     

SQL Server数据库应用程序性能优化方法

为提高基于SQL Server数据库应用程序的执行效率,分析了SQL Server数据库系统自身的查询优化处理技术,总结出多种基于SQL Server数据库的应用程序性能优化方法：选择性能优越的服务器;优化数据库设计;使用查询效率较高的查询语句;使用存储过程;有效的使用事务和批处理;避免阻塞;选择合适的开发工具和采用有效的数据库访问技术。     

Microsoft SQL Server数据库的安全策略及实现方法

结合正虹集团管理信息系统的开发,探讨了Microsoft SQL Server基于客户机／服务器结构的大型关系数据库系统中的安全管理策略一一安全帐户认证,访问许可确认,许可设置,根据信息系统开发过程中遇到的安全问题,从应用系统安全设计角度,给出了以下实现管理信息系统数据库安全方法的设计及实现过程一一身份验证,存取控制,隔离控制,审计和数据加密。     

Feedback control for optimal process operation

In chemical process operation, the purpose of control is to achieve optimal process operation despite the presence of significant uncertainty about the plant behavior and disturbances. Tracking of set-points is often required for lower-level control loops, but on the process level in most cases this is not the primary concern and may even be counterproductive. In this paper, different approaches how to realize optimal process operation by feedback control are reviewed. The emphasis is on direct optimizing control by optimizing an economic cost criterion online over a finite horizon where the usual control specifications in terms of, e.g., product purities enter as constraints and not as set-points. The potential of this approach is demonstrated by its application to a complex process which combines reaction with chromatographic separation. Issues for further research are outlined in the final section.     

Feedback control for non-linear singular systems

An invertible non-linear map is developed, which transforms a non-linear singular system into a regular one and preserves local properties under the application of specific feedback control laws. The presented algorithm is easily implementable on a digital computer, since it is of closed form. An application of the above algorithm is presented on an autonomous vehicle.     

Feedback equivalence for general control systems

We discuss the solution to the problem of local equivalence of control systems with n states and p controls in a neighbourhood of a generic point, under the Lie pseudo-group of local time independent feedback transformations. We have shown earlier that this problem is identical with the problem of simple equivalence of the time optimal variational problem. Here we indicate the way in which this identification may be used to obtain closed loop time critical controls for general systems. We show that the classification of general nonlinear systems depends on the classification of all n−p dimensional affine subspaces of the space of symmetric forms in p variables and that the case of control linear systems depends on the classification of all n−p dimensional affine subspaces of the space of skew forms in p variables. We show that in the latter case the G-structure is the prolongation of one determined by a state space transformation group. We give a complete list of normal forms for control linear systems in the case p=n−1.     

密码子用法数据库辅助工具CUDassist的开发

密码子用法的研究是遗传密码的进化、基因的水平转移、基因表达的调控和异源表达的优化等领域不可或缺的内容.2个重要的密码子用法在线服务密码子用法数据库(CUD)和图形化密码子用法分析器(GCUA)为研究者提供了有力的数据支持,但仍存在一些问题,如密码子用法数据库可接受的检索方式过于单一,在特定密码子用法表(CUT)中Fraction参数值显示有误,图形化密码子用法分析器仪提供2个密码子用法表的比对视图等.本文针对这些问题,研发了密码子用法数据库辅助工具"CUDassist",做出4个改进: (1)增加密码子用法数据库的可检索方式;(2)修正密码子用法数据库中Fraction值显示错误的问题;(3)在密码子用法表中直接给出相对适应度(RA)参数值;(4)提供多个密码子用法表的比对视图.从而为研究者提供更方便、准确和丰富的密码子用法的信息,并在一定程度上有效融合了密码子用法数据库和图形化密码子用法分析器的功能,实现一站式服务.     

Divergence control for distributed database systems

This paper presents distributed divergence control algorithms for epsilon serializability for both homogeneous and heterogeneous distributed databases. Epsilon serializability allows for more concurrency by permitting non-serializable interleavings of database operations among epsilon transactions. We first present a strict 2-phase locking divergence control algorithm and an optimistic divergence control algorithm for a homogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction are the same. In such an environment, the total inconsistency of a distributed epsilon transaction is simply the sum of those of all its sub-transactions. We then describe a divergence control algorithm for a heterogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction may not be the same and the total inconsistency of a distributed epsilon transaction may be greater than the sum of those of all its sub-transactions. As a result, in addition to executing a local divergence control algorithm in each site to maintain the local inconsistency, a global mechanism is needed to take into account the additional inconsistency Recommended by: Meichum Hsu     

基于语义的移动数据库同步服务器的设计

同步服务器在典型的三级复制移动数据库系统中扮演着重要的角色,也是整个移动数据库系统设计中的难点所在。在目前通用的数据复制副本模型的基础上,结合应用的语义信息,讨论了一种同步服务器的设计方法,并给出了具体的实现算法。     

多层Web服务器的准入控制研究

一般基于多层Web服务器的准入控制不能考虑到各层之间的相关性,且准入策略具有延迟性,极大地限制了系统吞吐量.针对这个问题,提出一种基于控制理论的2级模糊控制器:第1级控制器根据各层服务器的资源使用率和延迟情况来判别其他的负载情况;第2级服务器则根据各个层次服务器的负载情况,以概率形式判断是否拒绝或接受一个会话.通过实验验证,该算法可以有效地克服一般准入控制的局限性,提高系统吞吐量.     

A flexible and recoverable client/server database event notification system

A software architecture is presented that allows client application programs to interact with a DBMS server in a flexible and powerful way, using either direct, volatile messages, or messages sent via recoverable queues. Normal requests from clients to the server and replies from the server to clients can be transmitted using direct or recoverable messages. In addition, an application event notification mechanism is provided, whereby client applications running anywhere on the network can register for events, and when those events are raised, the clients are notified. A novel parameter passing mechanism allows a set of tuples to be included in an event notification. The event mechanism is particularly useful in an active DBMS, where events can be raised by triggers to signal running application programs. Received July 21, 1995 / Accepted May 30, 1996     

Cautious transaction schedulers for database concurrency control

Cautious schedulers, which never resort to rollbacks for the purpose of concurrency control, are investigated. In particular, cautious schedulers for classes WW consisting of schedules serializable under the write-write constraints, and WRW, a superclass of W, are considered. The cautious WW-scheduler has a number of nice properties, one of which is the existence of a polynomial-time scheduling algorithm. Since cautious WRW-scheduling is, in general, NP-complete, some restrictions are introduced which allow polynomial-time scheduling. All of these cautious schedulers are based on the assumption that transaction predeclare their read and write sets on arrival. Anomalies which occur when transaction modify their read sets or write sets during execution are discussed and countermeasures are proposed     

Minimizing time-space cost for database version control

Summary We introduce the concept of a version graph to model the problem of minimizing the combined cost of storage space and version regeneration time for database version control systems. We show that, in general, this problem and several of its variations are NP-complete. Several heuristics are developed, and performance guarantees for these heuristics are obtained. We also present linear time algorithms for special classes of version graphs; these special classes are likely to apply in many version control systems.Research supported in part by the National Science Foundation under Grant DCR 86-03184An extended abstract of this paper appeared in Proceedings of the Seventh ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, Austin, Texas, March 1988