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全序时态模式下函数依赖多值依赖混合集问题研究
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摘要
与时间相关的数据库应用需求的不断增长,使得时态数据库设计成为非常重要的问题。在数据库的设计中,要充分考虑对数据依赖的处理,数据依赖是指数据之间存在的各种联系,数据冗余的产生和数据依赖有着密切的联系。数据依赖是数据库设计理论中的一个核心概念,通过它可以规范属性之间满足的固有的语义约束。
     为了更有效的研究时态数据库中各种依赖以及各属性之间的关系,以便将关系进一步规范化,本文提出了时态左部属性、时态右部属性、时态双部属性、时态函数依赖图等概念。并分别利用图论法和吸收法给出了求时态候选关键字集的算法,并证明其正确性。
     时态函数依赖(Temporal Functional Dependency, TFD)和时态多值依赖(Temporal Multi-valued Dependency, TMVD)是时态数据库中最重要的两种数据依赖。对于具有TFD和TMVD混合集约束的时态模式来说,由于多时间粒度的使用使成员籍问题的解决变得更加复杂。但成员籍问题的解决对设计有效的模式分解算法必不可少,本文基于强全序时态模式以及全序时态函数依赖和规则时态多值依赖(RTMVD)理论提出了给定时态类型上的混合依赖基、强全序模式混合依赖基、TFD和RTMVD混合集闭包、强全序模式混合闭包等概念,并给出了求混合混依赖集中属性的依赖基、属性集的闭包的算法,对算法的可终止性、正确性进行了证明,并对时间复杂度进行了分析。在此基础上,给出了解决强全序模式混合集成员籍问题的算法,并对算法的可终止性、正确性进行了证明,对时间复杂度进行了分析。
     同时,本文提出了强全序时态模式中冗余依赖、混合无冗余覆盖、规范混合依赖集等概念,并给出了求强全序时态模式混合依赖集的无冗余覆盖和规范覆盖的算法。
     以上理论和算法的研究,很好的解决了强全序混合依赖集中依赖的判定的处理问题,为解决强全序时态模式规范化问题以及时态数据库设计提供了理论基础。
The ever increasing of database related to time makes designing temporal database very important. In the design of temporal database, it is necessary to give full consideration to the data dependent treatment. Data dependency means all kinds of connections among data. The happening of data redundance is connected with data dependency. Data dependency is a central notion in database design theory through which we can normalize intrinsic semantic restrinction among attributes.
     In order to make the study, the relation of all the dependences and all the attributes, more efficient, then normalize relational database one more step, in this paper, the notions of temporal left attributes, temporal right attributes, temporal both-rl attributes, temporal functional dependency graph are introduced. And the algorithms for temporal candidate keyword sets is given use graph theory method and absorption method respectively, its correction are given.
     Temporal functional dependency (TFD) and temporal multi-valued dependency (TMVD) are the two most important data-dependent in temporal database. For temporal scheme with temporal functional dependencies and temporal multi-valued dependencies constrains, the usages of multiple time granularities make it more difficult to solve membership problem. However, the solution of membership problem is essential to design an available algorithm of scheme decomposition. On the base of the strong totally orderd temporal scheme and totally orderd temporal functional dependency and the theory of regular temporal multi-valued dependency (RTMVD) of relational database, in this paper, the concepts of mix dependency base on given temporal type, mix dependency base in strong totally orderd scheme, TFD and RTMVD mix close set of strong totally orderd scheme are given. And the algorithms of dependency base of attribution sets, closure of attribution sets are given, then the proof for its termination, correction and time complexity are given. On this base, the algorithm of membership problem of mix set in strong totally orderd is given, and the proof for its termination, correction and time complexity are given.
     As well as, concepts of redundant dependency, mixed non-redundant cover and canonical mixed dependency set of strong-totally order temporal scheme are given. Corresponding algorithms, non-redundant cover and canonical cover, are proposed which can solve the cover problem of mixed dependency set in strong-totally orderd temporal scheme.
     The above research of theory and algorithm is a good solution to the problem of dependency judgement in a strong-totally mix-set of dependency, as well as, it provide theory basement for resolving the problem of normalization which in strong-totally ordered temporal scheme and the design of temporal database.
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