【作者】 张玲侠；

【导师】 陆奎；

【作者基本信息】 安徽理工大学 ， 计算机应用技术， 2008， 硕士

【摘要】 移动数据库作为分布式数据库的延伸和扩展,拥有分布式数据库的诸多优点和自身独特的特点,能够满足人们任何时候、任何地点能够访问任何信息的需求,有着十分广泛的应用前景。在移动数据库系统中,由于其移动性、频繁地断接性、网络条件多样性和资源有限性等特点,使得传统分布式数据库的技术不能有效地支持移动计算环境,因此有必要针对移动计算环境的特点研究新的处理技术。本文在广泛地查阅国内外文献的基础上,对移动数据库的同步复制技术和缓存技术进行了深入地研究,主要包括以下内容。1)在同步复制技术方面,首先在阐述二级复制技术并分析其特点的基础上,介绍了三级复制技术,接着针对第三级复制(客户机缓存)的一致性维护问题提出了定时增量维护算法,并分析了三级复制技术有效地支持移动计算环境的原因,最后对现有商用移动数据库产品的同步复制技术进行了对比分析。2)在缓存技术方面,首先阐述了传统的缓存技术并分析其不能适应移动数据库的原因,接着在分析现有优先级增量更新算法的基础上,针对此算法仅考虑视图中整体数据的平均时间因素的缺点,引入了数据复杂度和用户的访问概率等因素,提出了动态的优先级增量更新算法。该算法继承并完善了优先级增量更新算法中数据新鲜度的概念,根据访问概率将这种新鲜度用户化,同时加入了数据复杂度等因素,弥补了优先级增量更新算法的不足,有效地改善了移动数据视图更新的实时性和一致性等问题,更好地迎合了移动用户的需求。更多还原

【Abstract】 As the extension and expanding of the distributed database, mobile database, which has many excellences of distributed database and unique character itself, can satisfy the need that people want to get any information in any time wherever they are, therefore it has quite extensive foreground in application.In the mobile database system, because of the properties of the mobile environment such as mobility, frequent disconnection, network diversity, limited power .etc, the technique of the traditional distributed database can’t sustain effectively the mobile environment; hence the research for the technique in the mobile environment is to be essential.Based on the domestic and international information, this paper mainly studies the replication technique and cache technique of the mobile database.and has done the work as follows:1) About the replication technique, based on the two-tier-replication, this paper introduces three-tier-replication and then proposes the periodical incremental maintenance algorithms with regard to the third tier replication (mobile client cache). Furthermore, it analyses the reason why three-tier-replication technique sustains effectively the mobile environment.2) About the cache technique, firstly this paper elaborates the reason why the traditional cache technique can’t be effective in the mobile database and analyses the priority-based incremental update algorithm. Furthermore, one dynamic priority-based incremental update algorithms(DPIU) which considers two factors of data complexity and user’s access probability is proposed The DPIU, which inherits the concept of data fresh and adds factors such as data complexity, makes up the shortages of the priority-based incremental update algorithm. Hence, the algorithm improves effectively the real-time and consistency in view update of mobile database, meanwhile caters to the demand of the mobile users.更多还原