XML DTD的一种范式

研究了XML DTD的规范化问题。由于DTD在设计上存在不足之处，DTD中可能包含类似于关系数据库模式中存在的异常依赖，从而导致XML文档包含冗余的数据和各种操作异常。提出了关于DTD的多值依赖的概念，然后基于多值依赖的概念，提出了一种XML的范式XNF，并且用DTD的关系表示形式给出了关于DTD的无损联接分解的概念。最后给出了把DTD无损联接地分解成XNF的一种算法。     

XML的规范化与范式

给出了XML间接函数依赖和传递函数依赖的概念,据此提出了以DTD为模式的XML文档的一种范式XMLNF,它可以消除XML文档中由于间接函数依赖和传递函数依赖所引起的数据冗余,给出了把DTD无损联接地分解成XMLNF的规范化方法.     

存在多值依赖的XML DTD规范化研究

XML DTD文档中可能包含由非函数依赖引起的数据冗余和操作异常，首先从消除DTD文档内数据冗余的角度出发研究了文档的规范化的问题，讨论了在DTD文档中存在多值依赖的情况下，如何规范XML文档，提出了以DTD为模式的XML文档的多值依赖的概念。然后基于多值依赖的概念，提出了XML文档的一种多值依赖范式MXNF。最后在此基础上提出了把一个XML文档的DTD无损联接地分解成为符合MXNF的规范化算法，来规范存在多值依赖的XML DTD文档，并给出了该算法的分析说明。     

基于约束的XML文档规范化算法

XML模式设计是XML数据库设计的关键．基于XML文档的基本概念给出了XML部分函数依赖、传递函数依赖、XML范式、XML第1到第3范式以及DTD无损联接分解的相关定义,提出XML模式规范化转换规则,给出无损联接分解的两种规范化算法,对算法的正确性、可终止性和时间复杂性进行了证明分析,并实验证明了规范化后的文档查询和存储效率有明显的提高．这将对未来的XML函数依赖保持、XML多值依赖以及XML模式设计的进一步规范化研究奠定理论基础．     

XML DTD规范化处理应用研究

从消除XML DTD文档内数据冗余的角度出发研究了文档的规范化问题，首先引入XML DTD上路径和函数依赖的定义，并提出定义XML上的数据冗余；其次基于函数依赖，提出了规范化的DTD概念和XML DTD规范化处理规则；最后给出了一个将XML DTD转化为规范化的处理算法。     

XML函数依赖及其与键的关系

通过分析函数依赖的表现形式在XML文档和关系数据库中的不同之处，提出了基于DTD中的路径表达式的XML函数依赖的概念．并且给出了XML函数依赖的XML表示方法，研究了XML函数依赖和XML键的关系．     

XML多值依赖及其消除冗余模式的算法*

从消除XML文档内数据冗余的角度出发研究了文档的规范化问题.首先引入XML上的数据冗余及其消除处理示例,同时基于函数依赖,提出了规范化的DTD概念和XML DTD 规范化处理规则;其次通过XML多值依赖的定义,给出用于消除冗余模式的算法;最后给出用于XML模式及其消除冗余模式的算法.该算法相应于其他XML模式的研究,在算法产生的层次模式中,完全MVD和嵌入MVD的集合由给出的MVD集合导出;并且产生的XML模式具有消除冗余模式和满足无损连接的特性.     

XML上的函数依赖推理

函数依赖是数据语义的重要组成部分,这一概念被引入到XML的领域中.基于DTD,XML的树模型和路径表达式,对节点的值相等和路径节点集作了定义.在此基础上,研究了XML中函数依赖、逻辑蕴涵和路径闭包的概念,证明了函数依赖在给定DTD上的可满足性.提出了一个XML上函数依赖的正确和完备的推理规则集,并给出了一个用于计算路径闭包的算法.     

XML文档规范化算法研究

函数依赖对关系数据库和XML文档都是一种重要的语义表达.文中对XML文档中存在的函数依赖、部分函数依赖和传递函数依赖进行分析,对规范部分函数依赖提出XML第二范式,对规范部分函数依赖和传递函数依赖提出了XML第三范式,给出了相应算法,并进行了无损联接性和函数依赖保持性证明,对可终止性和时间复杂度进行了分析.     

XML文档规范化算法研究

函数依赖对关系数据库和XML文档都是一种重要的语义表达。文中对XML文档中存在的函数依赖、部分函数依赖和传递函数依赖进行分析,对规范部分函数依赖提出XML第二范式,对规范部分函数依赖和传递函数依赖提出了XML第三范式,给出了相应算法,并进行了无损联接性和函数依赖保持性证明,对可终止性和时间复杂度进行了分析。     

用于XML模式和DTD规范化设计的层次模式设计

XML模式和DTD(document type definition)规范化设计是给出一个很好地表示数据间依赖关系并消除了冗余的XML模式或DTD的集合.目前在这一方面开展的研究还不多,而且才刚起步.Provost提出将关系数据库理论应用于XML模式规范化设计的思想,这一思想还没有付诸实施.在Provost思想的基础上给出用于XML模式和DTD规范化设计的层次模式设计的算法.首先分析了基于Provost思想的层次分解;然后给出用于消除冗余模式的分解树设计算法;最后给出用于XML模式和DTD规范化设计的层次     

Mapping DTDs to relational schemas with semantic constraints

XML is becoming a prevalent format and standard for data exchange in many applications. With the increase of XML data, there is an urgent need to research some efficient methods to store and manage XML data. As relational databases are the primary choices for this purpose considering their data management power, it is necessary to research the problem of mapping XML schemas to relational schemas. The semantics of XML schemas are crucial to design, query, and store XML documents and functional dependencies are very important representations of semantic information of XML schemas. As DTDs are one of the most frequently used schemas for XML documents in these days, we will use DTDs as schemas of XML documents here. This paper proposes the concept and the formal definition of XML functional dependencies over DTDs. A method to map XML DTDs to relational schemas with constraints such as functional dependencies, domain constraints, choice constraints, reference constraints, and cardinality constraints over DTDs is given, which can preserve the structures of DTDs as well as the semantics implied by the above constraints over DTDs. The concepts and method of mapping DTDs to relational schemas presented in the paper can be extended to the field of XML Schema just with some modifications in related formal definitions.     

Dependency-preserving normalization of relational and XML data

Having a database design that avoids redundant information and update anomalies is the main goal of normalization techniques. Ideally, data as well as constraints should be preserved. However, this is not always achievable: while BCNF eliminates all redundancies, it may not preserve constraints, and 3NF, which achieves dependency preservation, may not always eliminate all redundancies. Our first goal is to investigate how much redundancy 3NF tolerates in order to achieve dependency preservation. We apply an information-theoretic measure and show that only prime attributes admit redundant information in 3NF, but their information content may be arbitrarily low. Then we study the possibility of achieving both redundancy elimination and dependency preservation by a hierarchical representation of relational data in XML. We provide a characterization of cases when an XML normal form called XNF guarantees both. Finally, we deal with dependency preservation in XML and show that like in the relational case, normalizing XML documents to achieve non-redundant data can result in losing constraints.     

一种理性的数据库模式设计方法--范式方法

介绍了一种理论性较强的数据库模式设计方法———范式方法。范式方法基于函数依赖及范式理论。最终的数据库模式必须满足BCNF模式集或3NF模式集、无损联接和保持函数依赖这三个特性才是一个可用的数据库,才不会出现各种操作异常(插入、删除)并且能大大地减少数据冗余。     

The implication problem for ‘closest node’ functional dependencies in complete XML documents

With the growing use of XML as a format for the permanent storage of data, the study of functional dependencies in XML (XFDs) is of fundamental importance in a number of areas such as understanding how to effectively design XML databases without redundancy or update problems, and data integration. In this article we investigate a particular type of XFD, called a weak ‘closest node’ XFD, that has been shown to extend the classical notion of a functional dependency in relational databases. More specifically, we investigate the implication problem for weak ‘closest node’ XFDs in the context of XML documents with no missing information. The implication problem is the most important one in dependency theory, and is the problem of determining if a set of dependencies logically implies another dependency. Our first, and main, contribution is to provide an axiom system for XFD implication. We prove that our axiom system is both sound and complete, and we then use this result to develop a sound and complete quadratic time closure algorithm for XFD implication. Our second contribution is to investigate the implication problem for XFDs in the presence of a Document Type Definition (DTD). We show that for a class of DTDs called structured DTDs, the implication problem for a set of XFDs and a structured DTD can be converted to the implication problem for a set of XFDs alone, and so is axiomatizable and efficiently solvable by the first contribution. We do this by augmenting the original set of XFDs with additional XFDs generated from the structure of the DTD.