基于树型结构的共享文档副本的语义一致性维护

锁操作在实时协同编著系统中用于共享文档副本的语义一致性维护.针对已有线性结构文档中锁操作转换算法效率低下的问题,对文档采用树型结构的表示方法,在文档的不同层级引入可选锁机制,并提出一个新的锁操作转换算法TreeLock_GOTO,大大提高了锁操作转换算法的执行效率.     

协同编辑系统中保持共享对象一致性的研究

如何保持共享对象的一致性是实时协同设计中的核心问题。文中介绍了一种新颖的保持共享对象一致性的方法。根据协同图形编辑系统中操作冲突的特点,使用消息驱动机制,配合同步机制和冲突检测与消解机制,使得系统既能保持共享对象的一致性,又满足了实时协同设计中的响应性、因果顺序一致性,并最大限度地保持了用户的操作目的。     

协同编辑系统中保持共享对象一致性的研究

如何保持共享对象的一致性是实时协同设计中的核心问题.文中介绍了一种新颖的保持共享对象一致性的方法.根据协同图形编辑系统中操作冲突的特点,使用消息驱动机制,配合同步机制和冲突检测与消解机制,使得系统既能保持共享对象的一致性,又满足了实时协同设计中的响应性、因果顺序一致性,并最大限度地保持了用户的操作目的.     

基于图形对象的一致性维护问题的研究

针对实时协同图形编辑系统中一致性维护关键问题,提出了一种基于图形对象的并发控制算法。该算法扩展了面向文本编辑的分布式操作转换dOPT算法,满足图形对象属性级上数据一致性维护,同时通过预定义图形对象间的关联关系和位置属性约束规则,进行操作语义维护管理,使得实时协同图形编辑系统的一致性维护更为有效和完备。     

集中式CSCW环境中对实时共享对象的并发控制算法

在实时CSCW环境中，必然存在多个用户都需要同时访问的共享对象，系统必须对用户访问对象的操作做出实时的响应，以使对象的变化与用户的期望相一致，本文提出了一种解决并发控制的方法，目标是在并发和实时的情况下实现多客户感知的对象一致性，算法基于变换和用户期望，利用前向变换来构建对象的历史记录。     

协同图形编辑系统多版本动态属性锁协议研究

在协同CAD系统中,解决设计者之问的冲突检测与消解问题是实现有效并发控制机制的关键。针对协同设计中多个关联对象之间的冲突检测和消解问题,介绍协同多版本相关概念和多版本属性标记锁策略,提出一种解决对象关联操作冲突的多版本动态属性锁并发控制协议,设计实现相应的算法。该协议将多版本和对象标记锁相结合,保证了并发冲突中的用户意愿。最后,分析多版本动态属性共享锁协议的正确性,并通过实例说明协议的可用性。     

协同图形编辑系统多版本动态属性锁协议研究

在协同CAD系统中,解决设计者之间的冲突检测与消解问题是实现有效并发控制机制的关键.针对协同设计中多个关联对象之问的冲突检测和消解问题,介绍协同多版本相关概念和多版本属性标记锁策略,提出一种解决对象关联操作冲突的多版本动态属性锁并发控制协议,设计实现相应的算法.该协议将多版本和对象标记锁相结合,保证了并发冲突中的用户意愿.最后,分析多版本动态属性共享锁协议的正确性,并通过实例说明协议的可用性.     

操作转换方法的分析和应用扩展

操作转换方法是实时协同编辑中进行并发控制的一种常用方法。论文首先介绍了复制式协同编辑系统的一致性模型,阐述了操作转换方法的基本流程,详细分析了七种典型操作转换方法实现三个一致性条件的方案。接着分析了操作转换方法的应用扩展,最后针对面向三维协同设计的应用扩展进行讨论。     

实时协同中的一致性维护关键技术

实时协同广泛采用数据复制技术来隐藏网络延迟、提高响应速度和改善交互体验。在复制式结构中,用户可以无约束地在不同数据副本上进行操作,这必然会引发一致性维护问题。针对上述问题,根据实时协同应用的特点和需求,总结一致性维护研究面临的技术挑战,通过研究实时协同中操作转换、地址空间转换和WOOT一致性维护的关键技术,讨论Undo和String转换等难点问题,分析这些关键技术在单用户软件向多用户协同软件透明转换、Web2.0环境和移动协同环境中的应用情况。     

以网络为中心的语义特征造型协同设计

在网络化同步协同设计环境中，如何实现用户系统之间的实时数据交换、维护特征语义的一致性，成为语义特征造型协同设计的关键问题。该文介绍了基于细胞元表示的语义特征模型，根据该造型技术的分层体系结构，基于对协同环境下特征操作的分析，采取了传输造型操作命令的策略，为解决特征语义一致性问题，提出了一种用操作特征管理器调度操作执行的方法，并给出了一个实例。     

基于相对位置的分布式实时协同编辑乐观锁并发控制算法

实时分布式协同编辑系统是计算机支持的协同工作的典型应用系统,不少学者对其进行了大量的研究,其难点是协作编辑的一致性、实时性和无约束性。因此,并发控制始终是它的研究热点,目前已提出的协同编辑的并发控制算法有:传统的加锁法、tickle锁、floor控制、可逆执行(Undo/Redo)和操作转换等。传统的加锁法最突出的优点是设计和实现较为简单,能保证具体上下文的语义完整性,但是在分布式协同编辑中无法保证加锁位置的一致性。tickle锁方法适用于分节加锁的实时分布式协同编辑的并发控制,然而无法提供多个编辑者对节内的同时编辑。JCE中的协同编辑采用了floor控制方法,每个协作编者只有获得floor才能进行     

相对位置乐观锁机制及在协同编辑中的应用

为了满足实时协同编辑对快速响应、无约束协作的要求，提出了一种基于相对位置的乐观锁机制并发控制算法．该算法引入了编辑锁和读锁，并对加锁的起始位置和编辑操作位置用相对位置表示，当锁申请成功将写进锁表或者操作发送到各协作结点时，再把它们转换成绝对位置，加锁的粒度可根据编者的需要任意选择，编者在加锁请求获得确认前，可预先进行编辑操作．应用实例表明：该算法既保证了数据维护的一致性，又具有快速响应性．     

Locking protocols for materialized aggregate join views

The maintenance of materialized aggregate join views is a well-studied problem. However, to date the published literature has largely ignored the issue of concurrency control. Clearly, immediate materialized view maintenance with transactional consistency, if enforced by generic concurrency control mechanisms, can result in low levels of concurrency and high rates of deadlock. While this problem is superficially amenable to well-known techniques, such as fine-granularity locking and special lock modes for updates that are associative and commutative, we show that these previous high concurrency locking techniques do not fully solve the problem, but a combination of a "value-based" latch pool and these previous high concurrency locking techniques can solve the problem.     

Optional and responsive fine-grain locking in Internet-based collaborative systems

Locking is a standard technique used in distributed computing and database systems to ensure data integrity by prohibiting concurrent conflicting updates on shared data objects. Internet-based collaborative systems are a special class of distributed applications which support human-to-human interaction and collaboration over the Internet. In this paper, a novel optional and responsive fine-grain locking scheme is proposed for consistency maintenance in Internet-based collaborative editors. In the proposed scheme, locking is made optional in the sense that a user may update any part of the document without necessarily requesting a lock. In the face of high communication latency in the Internet environment, responsive locking is achieved by granting the permit to the user for updating the data region immediately after issuing a locking request. Moreover, multiple fine-grain locks can be placed on different regions inside a document to allow concurrent and mutually exclusive editing on the same document. Protocols and algorithms for locking conflict resolution and consistency maintenance are devised to address special technical issues involved in optional and responsive fine-grain locking. The proposed locking scheme and supporting techniques were implemented in an Internet-based collaborative editor to demonstrate its feasibility and usability.     

Object-based semantic real-time concurrency control with boundedimprecision

The paper describes a concurrency control technique for real-time object-oriented databases that supports logical consistency and temporal consistency, as well as bounded imprecision that results from their trade-offs. The concurrency control technique uses a semantic locking mechanism within each object and user-defined conditional compatibility over the methods of the object. The semantics can specify when to sacrifice precise logical consistency to meet temporal consistency requirements. It can also specify accumulation and bounding of any resulting logical imprecision. The authors show that this technique, under certain general restrictions, can preserve global correctness and bound imprecision by proving it can guarantee a form of epsilon serializability specialized for object-oriented databases     

Performance of program modification techniques that ensure serializable executions with snapshot isolation DBMS

Snapshot Isolation (SI) is a multiversion concurrency control that has been implemented by several open source and commercial database systems (Oracle, Microsoft SQL Server, and previous releases of PostgreSQL). The main feature of SI is that a read operation does not block a write operation and vice versa, which allows higher degree of concurrency than traditional two-phase locking. SI prevents many anomalies that appear in other isolation levels, but it still can result in non-serializable executions, in which database integrity constraints can be violated. Several techniques are known to modify the application code based on preanalysis, in order to ensure that every execution is serializable on engines running SI. We introduce a new technique called External Lock Manager (ELM). In using a technique, there is a choice to make, of which pairs of transactions need to have conflicts introduced. We measure the performance impact of the choices available, among techniques and conflicts.     

Asynchronous operations in distributed concurrency control

Distributed locking is commonly adopted for performing concurrency control in distributed systems. It incorporates additional steps for handling deadlocks. This activity is carried out by methods based on wait-for-graphs or probes. The present study examines detection of conflicts based on enhanced local processing for distributed concurrency control. In the proposed "edge detection" approach, a graph-based resolution of access conflicts has been adopted. The technique generates a uniform wait-for precedence order at distributed sites for transactions to execute. The earlier methods based on serialization graph testing are difficult to implement in a distributed environment. The edge detection approach is a fully distributed approach. It presents a unified technique for locking and deadlock detection exercises. The technique eliminates many deadlocks without incurring message overheads.     

Transaction management issues in a failure-prone multidatabase system environment

This paper is concerned with the problem of integrating a number of existing off-the-shelf local database systems into a multidatabase system that maintains consistency in the face of concurrency and failures.The major difficulties in designing such systems stem from the requirements that local transactions be allowed to execute outside the multidatabase system control, and that the various local database systems cannot participate in the execution of a global commit protocol. A scheme based on the assumption that the component local database systems use the strict two-phase locking protocol is developed. Two major problems are addressed: How to ensure global transaction atomicity without the provision of a commit protocol, and how to ensure freedom from global deadlocks.     

一种集成组播代理和操作转换的并发控制方法

摘　要：现有的分布式实时协作系统多采用操作转换的方法来提供并发控制服务,但是在系统数据量很大时,系统性能不高.为解决这一问题,提出了一种新的并发控制方法madOPT:该方法利用对象所定义的操作的语义进行冲突解析,集数据对象的动态载入、数据传输和操作转换功能为一体.madOPT改进了dOPT(distributed operation transformation)算法在操作转换过程中对操作日志的遍历以提高并发控制效率,并将对象属性作为并发控制的粒度,使之支持对图形、图像对象的并发操作;同时结合组播代理,提高数据传输率,使系统整体性能得到改善.     

A multi-granularity locking model for concurrency control inobject-oriented database systems

A locking model adopting a multi-granularity approach is proposed for concurrency control in object-oriented database systems. The model is motivated by a desire to provide high concurrency and low locking overhead in accessing objects. Locking in schemas and locking in instances are developed separately and then are integrated. Schema changes and composite objects are also taken into account. A dual queue scheme for efficient scheduling of lock requests is developed. The model consists of a rich set of lock modes, a compatibility matrix, and a locking protocol. Characteristic query examples on single class, class lattice, and composite objects are used to illustrate the comparison between the ORION model and the proposed model. It is shown that our locking model has indeed made some improvements and is suitable for concurrency control in object-oriented databases