消除结构冗余的XML数据库模式规范化设计

XML数据库模式规范化设计是给出一个能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．目前这一领域的研究并没有对XML数据库模式中的数据依赖和冗余进行专门的分析．引人标识符分别表示XML模式中的元素和属性，分析XML数据库模式的结构冗余：局部冗余、传递冗余和不规则；并在此基础上，定义XML数据库模式第3范式(3NF)，给出并验证其规范化设计算法．     

A comparative study of various nested normal forms

As object-relational databases (ORDBs) become popular in the industry, it is important for database designers to produce database schemes with good properties in these new kinds of databases. One distinguishing feature of an ORDB is that its tables may not be in first normal form. Hence, ORDBs may contain nested relations along with other collection types. To help the design process of an ORDB, several normal forms for nested relations have recently been defined, and some of them are called nested normal forms. In this paper, we investigate four nested normal forms, which are NNF [20], NNF [21], NNF [23], and NNF [25], with respect to generalizing 4NF and BCNF, reducing redundant data values, and design flexibility. Another major contribution of this paper is that we provide an improved algorithm that generates nested relation schemes in NNF [20] from an a-acyclic database scheme, which is the most general type of acyclic database schemes. After presenting the algorithm for NNF [20], the algorithms of all of the four nested normal forms and the nested database schemes that they generate are compared. We discovered that when the given set of MVDs is not conflict-free, NNF [20] is inferior to the other three nested normal forms in reducing redundant data values. However, in all of the other cases considered in this paper, NNF [20] is at least as good as all of the other three nested normal forms     

Temporal relational data model

This paper incorporates a temporal dimension to nested relations. It combines research in temporal databases and nested relations for managing the temporal data in nontraditional database applications. A temporal data value is represented as a temporal atom; a temporal atom consists of two parts: a temporal set and a value. The temporal atom asserts that the value is valid over the time duration represented by its temporal set. The data model allows relations with arbitrary levels of nesting and can represent the histories of objects and their relationships. Temporal relational algebra and calculus languages are formulated and their equivalence is proved. Temporal relational algebra includes operations to manipulate temporal data and to restructure nested temporal relations. Additionally, we define operations to generate a power set of a relation, a set membership test, and a set inclusion test, which are all derived from the other operations of temporal relational algebra. To obtain a concise representation of temporal data (temporal reduction), collapsed versions of the set-theoretic operations are defined. Procedures to express collapsed operations by the regular operations of temporal relational algebra are included. The paper also develops procedures to completely flatten a nested temporal relation into an equivalent 1 NF relation and back to its original form, thus providing a basis for the semantics of the collapsed operations by the traditional operations on 1 NF relations     

XML模式中隐式冗余不存在的充要条件

XML数据库模式规范化设计是产生一组相关联的、能表示数据间依赖关系、而且消除了冗余的XML模式或DTD,以更好地进行信息检索.XML数据库模式中某些数据依赖的存在是冗余存在的原因,因此在XML数据库模式中数据依赖与冗余的关联是其规范化设计研究的关键问题,但对这一问题目前还没有专门的研究.XML数据库模式的数据依赖包括属性间数据依赖和元素间的数据依赖,给出综合了属性间和元素间数据依赖的XML数据库模式数据依赖的定义,分析与之关联的隐式冗余,并论证XML模式中隐式冗余不存在当且仅当该XML模式是规范的,为XML数据库模式规范化设计更深一层的研究奠定理论基础.     

A New Approach to Database Auto-Design by Logic

The database auto-design is an important problem in database research.In this paper we propose some new ideas and an approach called “logic approach” to implement the database auto-design.Given a relational scheme and a set of the functional dependencies for the relation we can obtain all of the functional dependencies and key for the relation and determine the normal form the relation satisfies.     

Polynomial Tests of Normal Forms and Some Related Results

The following problem is called the everywhere-cover problem:“Given a set of dependencies over a database scheme,is he set of dependencies explicitly given for each relation scheme equivalent to the dependencies implied for that relation sheme?”It is shown that when the everywhere-cover problem has a yes answer,examining only the dependencies explicitly given will suffice to test 3NF, BCNF and 4NF of a database scheme.But this does not hold for 2NF.Consequently,in such cases,tests of BCNF and 4NF all take polynomial time.Then a proof is given that test of 3NF of a database scheme is Co-NP-complete,and from this result it is shown that everywhere-cover is also Co-NP-complete when only functional dependencies are allowed.These results lead to doubt the truth of the well believed conjecture that no polynomial time algorithm for designing a lossless BCNF database scheme is likely to exist.     

A parallel algorithm for relational database normalization

The problem of database normalization in a parallel environment is examined. Generating relation schemes in third normal form is straightforward when given a set of functional dependencies that is a reduced cover. It is shown that a reduced cover for a set of functional dependencies can be produced in parallel. The correctness of the algorithm is based on two important theorems. it is demonstrated that the companion third normal form algorithm can be easily translated into a parallel version. The performance of the two algorithms is compared to the performance of their serial counterparts. The standard serial algorithms for computing minimal covers and synthesizing third normal form relations are presented. The parallel algorithms and their rationale are discussed     

Semantic foundations of 4NF in relational database design

The issue of providing a formal justification for the use of fourth normal form (4NF) in relational database design is investigated. The motivation and formal definitions for three goals of database design are presented. These goals are the elimination of: redundancy, key-based update anomalies and fact-based replacement anomalies. It is then shown that, depending on the type of constraints permitted, either Boyce-Codd normal form (BCNF) or 4NF are the exact conditions needed to ensure most of the design goals. However, it is also shown that the conditions required to ensure the absence of a particular class of key-based update anomaly are new normal forms which have not previously been identified. In particular, for the case where the only constraints are functional dependencies (FDs), it is shown that the required normal form is a new normal form that is stronger than third normal form (3NF) yet weaker than BCNF. Similarly, in the more general case where both FD and multivalued dependencies (MVDs) are present, the required normal form is a new normal form that is weaker than 4NF. Received: 7 July 1995 / 28 December 1998     

Enhanced ER to relational mapping and interrelational normalization

This paper develops a method that maps an enhanced Entity-Relationship (ER+) schema into a relational schema and normalizes the latter into an inclusion normal form (IN-NF). Unlike classical normalization that concerns individual relations only, IN-NF takes interrelational redundancies into account and characterizes a relational database schema as a whole. The paper formalizes the sources of such interrelational redundancies in ER+ schemas and specifies the method to detect them. Also, we describe briefly a Prolog implementation of the method, developed in the context of a Computed-Aided Software Engineering shell and present a case study.     

Containment and disjointedness in partitioned normal form relations

Containment and disjointedness are two important properties in the updating materialized views. Disjointedness means that the set of tuples to be inserted in the view are disjoint from the view, and containment means that the tuples to be deleted from the view are contained in the view. In this paper we consider how to extend the definition of containment and disjointedness from flat relations to nested relations which are in partitioned normal form. The two correctness requirements that we place on our definitions are that they must be faithful and precise; where faithful means that the definition should coincide with the corresponding definition for flat relations when the nested relations are flat, and precise means that the definition should coincide with the corresponding definition for flat relations after performing a total unnest on the nested relation. We then propose definitions for disjointedness and containment for partitioned normal form relations and prove that the definitions proposed are faithful and precise. We also show that simple set based extensions of the definitions for flat relations are not correct since they are not precise. Received: 9 October 2000 / 17 September 2001     

多时间粒度约束的时态简单范式的分解

数据库逻辑设计的目的是消除数据冗余、插入和删除异常。为使时态模式满足某种范式的要求，要对时态模式进行分解，保持函数依赖和无损连接性是对算法最基本的要求。但对具有多时间粒度的时态模式进行分解时，把TBCNF作为最终目标很难实现保持函数依赖性，把T3NF作为最终目标，又很难达到规范化要求。该文提出了时态简单范式TSNF的概念及相应的分解算法，来弥补以上两点不足。     

Datalog extension for nested relations

The nested relational model allows relations that are not in first normal form. This paper gives an extension of Datalog rules for nested relations. In our approach, nested Datalog is a natural extension of Datalog introduced for the relational data model. A nested Datalog program has a hierarchical structure of rules and subprograms to manipulate relation values of nested relations. We introduce a new category of predicate symbols, the variable predicate symbols to refer to tuples of subrelations. The notion of soundness, safety and consistency is defined to avoid undesirable nested Datalog programs. The evaluation of nested Datalog is given in terms of the nested relational algebra. Finally, we relate the expressive power of nonrecursive nested Datalog to the power of nested relational algebra and safe nested tuple relational calculus.     

Normalization and lossless join decomposition of similarity‐based fuzzy relational databases

Fuzzy relational database models generalize the classical relational database model by allowing uncertain and imprecise information to be represented and manipulated. In this article, we introduce fuzzy extensions of the normal forms for the similarity‐based fuzzy relational database model. Within this framework of fuzzy data representation, similarity, conformance of tuples, the concept of fuzzy functional dependencies, and partial fuzzy functional dependencies are utilized to define the fuzzy key notion, transitive closures, and the fuzzy normal forms. Algorithms for dependency preserving and lossless join decompositions of fuzzy relations are also given. We include examples to show how normalization, dependency preserving, and lossless join decomposition based on the fuzzy functional dependencies of fuzzy relation are done and applied to some real‐life applications. © 2004 Wiley Periodicals, Inc. Int J Int Syst 19: 885–917, 2004.     

城市环境信息系统数据库设计及最小覆盖算法

本文设计了城市环境信息系统(CEIS)数据库，并探讨了该数据库的三范式问题，最后提出了数据库函数依赖的最小覆盖，解决了数据库的冗余问题。     

Framework design of a domain-key schema of a relational database

A new approach to the synthesis of the domain-key normal form (DK/NF) for an arbitrary domain is proposed. The Cartesian dependency, which is a special case of multivalued dependencies, is investigated. A lemma on the non-abnormality of a special relational and a theorem on the non-abnormality of the actual part of a relational framework are proved. A new criterion for determining the belonging of a database schema to DK/NF is given. The proposed approach can be used in designing information warehouse schemas.     

Propagating XML constraints to relations

We present a technique for refining the design of relational storage for XML data. The technique is based on XML key propagation: given a set of keys on XML data and a mapping (transformation) from the XML data to relations, what functional dependencies must hold on the relations produced by the mapping? With the functional dependencies one can then convert the relational design into, e.g. 3NF, BCNF, and thus develop efficient relational storage for XML data. We provide several algorithms for computing XML key propagation. One algorithm is to check whether a functional dependency is propagated from a set of XML keys via a predefined mapping; this allows one to determine whether or not the relational design is in a normal form. The others are to compute a minimum cover for all functional dependencies that are propagated from a set of XML keys and hold on a universal relation; these provide guidance for how to design a relational schema for storing XML data. These algorithms show that XML key propagation and its associated minimum cover can be computed in polynomial time. Our experimental results verify that these algorithms are efficient in practice. We also investigate the complexity of propagating other XML constraints to relations. The ability to compute XML key propagation is a first step toward establishing a connection between XML data and its relational representation at the semantic level.     

On Normalization of Relations in Relational Databases

A new normal form, namely, object-normal form (ONF), is introduced. It is shown that the existing definitions of the fifth normal form (5NF) are unsatisfactory. The correct definition is given for the first time. The importance of the 5NF is demonstrated. For improving data representation in a database with a 5NF schema, the notion of negating relation is introduced. It serves as a basis for the new normal form, namely, the sixth normal form. Combining requirements of the ONF and other normal forms, new normal forms are defined: the fourth object-normal form, the fifth object-normal form, and the sixth object-normal form. It is shown that the standard order of steps of the normalization procedure should be changed: first, the specific requirements of the fourth normal form should be satisfied, and only then the requirements of the second normal form, and so forth.     

Decomposition for a new kind of imprecise information system

In this paper, we first propose a new kind of imprecise information system, in which there exist conjunctions (∧’s), disjunctions (∨’s) or negations (¬’s). Second, this paper discusses the relation that only contains ∧’s based on relational database theory, and gives the syntactic and semantic interpretation for ∧ and the definitions of decomposition and composition and so on. Then, we prove that there exists a kind of decomposition such that if a relation satisfies some property then it can be decomposed into a group of classical relations (relations do not contain ∧) that satisfy a set of functional dependencies and the original relation can be synthesized from this group of classical relations. Meanwhile, this paper proves the soundness theorem and the completeness theorem for this decomposition. Consequently, a relation containing ∧’s can be equivalently transformed into a group of classical relations that satisfy a set of functional dependencies. Finally, we give the definition that a relation containing ∧’s satisfies a set of functional dependencies. Therefore, we can introduce other classical relational database theories to discuss this kind of relation.     

XML schema refinement through redundancy detection and normalization

As XML becomes increasingly popular, XML schema design has become an increasingly important issue. One of the central objectives of good schema design is to avoid data redundancies: redundantly stored information can lead not just only to a higher data storage cost but also to increased costs for data transfer and data manipulation. Furthermore, such data redundancies can lead to potential update anomalies, rendering the database inconsistent. One strategy to avoid data redundancies is to design redundancy-free schema from the start on the basis of known functional dependencies. We observe that XML databases are often “casually designed” and XML FDs may not be determined in advance. Under such circumstances, discovering XML data redundancies from the data itself becomes necessary and is an integral part of the schema refinement (or re-design) process. We present the design and implementation of the first system, DiscoverXFD, for efficient discovery of XML data redundancies. It employs a novel XML data structure and introduces a new class of partition-based algorithms. The XML data redundancies are defined on the basis of a new notion of XML functional dependency (XML FD) that (1) extends previous notions by incorporating set elements into the XML FD specification, and (2) maintains tuple-based semantics through the novel concept of Generalized Tree Tuple (GTT). Using this comprehensive XML FD notion, we introduce a new normal form (GTT-XNF) for XML documents, and provide comprehensive comparisons with previous studies. Given the set of data redundancies (in the form of redundancy-indicating XML FDs) discovered by DiscoverXFD, we describe a normalization algorithm for converting any original XML schema into one in GTT-XNF.     

一个多时间粒度下时态模式的T3NF分解算法

对于时态数据库，时间维的引入使得如何有效地进行数据库设计以消除数据冗余和插入、删除异常显得尤为重要．可以通过支持多时间粒度的时态函数依赖（TFDs）约束对时态数模式进行规范化．但是多时间粒度的使用给数据库设计带来巨大的复杂性．一般来说，系统所能处理的和相当多的应用所涉及到的时态类型集满足全序关系．对于这种具有全序时态类型集的时态模式，通过分析TFD臬所具有的良好特性，给出了一个得到满足时态第三范式（T3NF）的无损分解的多项式时间的算法．