基于本体的关系数据库语义检索

以经济学领域本体为例,首先研究SemSORD基本原理和方法,然后提出基于关系数据库关键词检索(Keyword Search over Relational Databases,KSORD)技术实现的关系数据库语义检索模型,并实现相应的原型系统Si-SEEKER,最后提出该领域的研究挑战和技术发展趋势.     

The integrity constraints for similarity-based fuzzy relational databases

This paper first introduces a new definition for the conformance of tuples existing in a similarity-based fuzzy database relation. Then the formal definitions of fuzzy functional and multivalued dependencies are given on the basis of the conformance values presented here. These dependencies are defined to represent relationships between domains of the same relation that exist. The definitions of the fuzzy dependencies presented in this study allow a sound and complete set of inference rules. In this paper, we include examples to demonstrate how the integrity constraints imposed by these dependencies are enforced whenever a tuple is to be inserted or to be modified in a fuzzy database relation. © 1998 John Wiley & Sons, Inc.     

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.     

A semantic framework of the multilevel secure relational model

A multilevel relational database represents information in a multilevel state of the world, which is the knowledge of the truth value of a statement with respect to a level in a security lattice. The authors develop a semantic framework of the multilevel secure relational model with tuple-level labelling, which formalizes the notion of validity in multilevel relational databases. They also identify the multilevel security properties that precisely characterize the validity of multilevel relational databases, which can be maintained efficiently. Finally, they give an update semantics of the multilevel secure relational model that preserves both integrity and secrecy     

OceanBase分布式关系数据库架构与技术

关系数据库是当今社会的关键信息基础设施,互联网和数字化带来了高并发和海量数据,传统关系数据库均为集中式架构,处理能力和存储容量都捉襟见肘. OceanBase分布式关系数据库基于通用PC服务器,不仅实现了在线水平伸缩,还实现了机房故障自动无损容灾以及高倍率数据压缩等,已经应用于金融、政务、通信和互联网等行业. 介绍了OceanBase分布式关系数据库的系统架构和关键技术,包括分布式事务处理、基于LSM-tree 的存储系统以及分布式SQL优化器. 详细阐述了OceanBase数据库的高可用和数据一致性,包括RPO为0和RTO小于8 s. 也介绍了OceanBase数据库多租户机制,即采用了集群内原生多租户设计,在集群内实现多个互相独立的数据库服务. 基于Sysbench和TPC-H评测基准,对比实验结果表明：1）在单机模式下,OceanBase的性能是MySQL的1.27倍至2倍多;2）在单主模式下,OceanBase的性能是MySQL的1.25倍至近2倍;3）在多主模式下,OceanBase的性能是MySQL的1.09倍至3.1倍,对于OLAP的复杂查询,OceanBase 的性能是MySQL 的6 倍到327倍.

     

A graphical interpretation of dependency structures in relational data bases

The designer of a relational data base must use dependency structures of data to model semantic situations that arise in data. He must further ensure that these dependencies are not violated during operations on the data base. In this paper we study a subclass of dependencies, namely, root-dependencies and introduce a common graphical picture (S-diagram) for all of them. This effort offers a possible application of graph theory to the study of relational data bases. The S-diagram offers a pictorial insight to all the root-dependencies. We also discuss, briefly, other possible uses of our work such as automatic constraint checking and recovery of data in a damaged data base.     

Integrity constraints of manufacturing data bases

Today's manufacturing cost reduction and competitiveness largely depends on the application of automated manufacturing. Automated manufacturing could be even more efficient if computerizations of the process is taken one step further—to the integration of the design and manufacturing processes by means of or through a well-structured data base. This paper refers to several important issues related to integrity constraints in relational data bases. The literature review provides a summary of what has been done in this area by other researchers. In addition, some of the concepts proposed, developed, and even implemented before are introduced. A brief look at the classification of integrity constraints is performed by examining the real world and engineering and manufacturing worlds. This classification is supported by various manufacturing examples for each type of integrity constraints. Further, we discuss the issues of how to express and manage integrity constraints in relational data bases with particular emphasis on manufacturing applications.     

Cardinality constraints in semantic data models

Constraints are central to the notion of a semantic data model. How well a model captures constraints affects its power and viability as a semantic data model. Cardinality constraints are an important subclass of general constraints. In this paper we provide formal definitions for cardinality constraints of several semantic models, as described in the literature. We construct a partial ordering of these constraints that shows the relative power expressed by each cardinality constraints. We discuss our results and offer possible extensions to contemporary cardinality constraint definitions. Our contributions include a collection and formal definition of existing cardinality constraints, a partial ordering of this set, and recommendations for cardinality constraint mechanisms in semantic data models.     

Refining imprecise data by integrity constraints

Uncertain data in databases were originally denoted as null values, which represent the meaning of ‘values unknown at present.” Null values were generalized into partial values, which correspond to a set of possible values, to provide a more powerful notion. In this paper, we derive some properties to refine partial values into more informative ones. In some cases, they can even be refined into definite values. Such a refinement is possible when there exist range constraint on attribute domains, or referential integrities, functional dependencies, or multivalued dependencies among attributes.

Our work actually eliminates redundant elements in a partial value. By this process, we not only provide a more concise and informative answer to users, but also speedup the computation of queries issued afterward. Besides, it reduces the communication cost when imprecise data are requested to be transmitted from one site to another site in a distributed environment.     

Inverted structure — A relational model for data identification

The inverted structure is proposed as a relational model of the information kernel in diagnostic and expert systems. The inverted structure can be used for identification of stored data by collections of attributes. The properties of the join operation on partially defined relations and issues of semantic integrity of data are discussed.Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 144–164, May–June 1992.     

A belief-consistent multilevel secure relational data model

Multilevel relations, based on the current multilevel secure (MLS) relational data models, can present a user with information that is difficult to interpret and may display an inconsistent outlook about the views of other users. Such ambiguity is due to the lack of a comprehensive method for asserting and interpreting beliefs about information at lower security levels. In this paper we present a belief-consistent MLS relational database model which provides an unambiguous interpretation of all visible information and gives the user access to the beliefs of users at lower security levels, neither of which was possible in any of the existing models. We identify different beliefs that can be held by users at higher security levels about information at lower security levels, and introduce a mechanism for asserting beliefs about all accessible tuples. This mechanism provides every user with an unambiguous interpretation of all viewable information and presents a consistent account of the views at all levels visible to the user. In order to implement this assertion mechanism, new database operations, such as verify true and verify false, are presented. We specify the constraints for the write operations, such as update and delete, that maintain belief consistency and redefine the relational algebra operations, such as select, project, union, difference and join.     

CEVCLUS: evidential clustering with instance-level constraints for relational data

Recent advances in clustering consider incorporating background knowledge in the partitioning algorithm, using, e.g., pairwise constraints between objects. As a matter of fact, prior information, when available, often makes it possible to better retrieve meaningful clusters in data. Here, this approach is investigated in the framework of belief functions, which allows us to handle the imprecision and the uncertainty of the clustering process. In this context, the EVCLUS algorithm was proposed for partitioning objects described by a dissimilarity matrix. It is extended here so as to take pairwise constraints into account, by adding a term to its objective function. This term corresponds to a penalty term that expresses pairwise constraints in the belief function framework. Various synthetic and real datasets are considered to demonstrate the interest of the proposed method, called CEVCLUS, and two applications are presented. The performances of CEVCLUS are also compared to those of other constrained clustering algorithms.     

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     

The mediator authorization-security model for heterogeneous semantic knowledge bases

Many organizations often need to share semantic knowledge base content with selected members of other organizations. However, sharing semantic knowledge across different organizations is a critical problem. This is because the differences in the vocabulary utilized by the organizations have to be resolved before knowledge can be shared. Also, if semantic repositories are syntactically and schematically heterogeneous, information interoperation becomes a vital challenge. When a system needs to allow unknown entities to access its resources, mechanisms should be in place in order to provide a secure and trusted information-sharing environment and enable users to interact and share information easily and perfectly. To address these challenges, the Mediator Authorization-Security model is proposed to provide secure interoperation among heterogeneous semantic repositories. This paper addresses the issue of interoperability and how to incorporate trust into semantic interoperability. The evaluation showed that, despite the complexity of the mediator system, it still provides acceptable performance.     

A semantic enriched data model for sensor network interoperability

One of the main open issues in the development of applications for sensor network management is the definition of interoperability mechanisms among the several monitoring systems and heterogeneous data. Interesting researches related to integration techniques have taken place, they are primary based on the adoption of sharing data mechanisms. In the last years, the Service-Oriented Architecture (SOA) approach has become predominant in many sensor network projects as it enables the cooperation and interoperability of different sensor platforms at an higher level of abstraction. In this paper we propose a novel architecture for the interoperability of sensor networks, which is based on web services technologies and on a common data model enriched with semantic concepts and annotations. The proposed architecture allows the development of complex decision support system applications by integration of heterogeneous data, accessible through services, according to standard data format and standard protocols.