A Methodology for Data Schema Integration in the Entity Relationship Model

The conceptual design of databases is usually seen as divided into two steps: view modeling, during which user requirements are formally expressed by means of several user oriented conceptual schemata, and schema integration, whose goal is to merge such schemata into a unique global conceptual schema. This paper is devoted to describe a methodology for schema integration. An enriched entity relationship model is chosen as the data model. The integration process consists of three steps: first, several types of conflicts between the different user schemata are checked and solved; second, schemata are merged into a draft integrated schema, that is, third, enriched and restructured according to specific goals.     

View creation for queries in object oriented databases

A view in object oriented databases corresponds to virtual schema with restructured generalization and decomposition hierarchies,Numbers of view creation methodologies have been proposed.A major drawback of existing methodologies is that they do not maintain the closure property.That is,the result of a query does not have the same semantics as embodied in the object oriented data model.Teherefore,this paper presents a view creation methodology that derives a class in response to a user‘s query,integrates derived class in global schema (i.e., considers the problem of classes moving in class hierarchy)and selects the required classes from global schema to create the view for user‘s query.Novel idea of view creation includes:(a) an object algebra for class derivation and customization(where the derived classes in terms of object instances and procedure/methods are studied),(b)maintenance of closure property,and (c)classification algorithm which provides mechanism to deal with the problem of a class moving in a class hierarchy.     

Model independent assertions for integration of heterogeneous schemas

Due to the proliferation of database applications, the integration of existing databases into a distributed or federated system is one of the major challenges in responding to enterprises' information requirements. Some proposed integration techniques aim at providing database administrators (DBAs) with a view definition language they can use to build the desired integrated schema. These techniques leave to the DBA the responsibility of appropriately restructuring schema elements from existing local schemas and of solving inter-schema conflicts. This paper investigates theassertion-based approach, in which the DBA's action is limited to pointing out corresponding elements in the schemas and to defining the nature of the correspondence in between. This methodology is capable of: ensuring better integration by taking into account additional semantic information (assertions about links); automatically solving structural conflicts; building the integrated schema without requiring conforming of initial schemas; applying integration rules to a variety of data models; and performing view as well as database integration. This paper presents the basic ideas underlying our approach and focuses on resolution of structural conflicts.     

A self-organizing knowledge representation scheme for extensibleheterogeneous information environment

The self-organizing knowledge representation aspects in heterogeneous information environments involving object-oriented databases, relational databases, and rulebases are investigated. The authors consider a facet of self-organizability which sustains the structural semantic integrity of an integrated schemea regardless of the dynamic nature of local schemata. To achieve this objective, they propose an overall scheme for schema translation and schema integration with an object-oriented data model as common data model, and it is shown that integrated schemata can be maintained effortlessly by propagating updates in local schemata to integrated schemata unambiguously     

Global extensional assertions and local integrity constraints in federated schemata

Integrated access to multiple data sources requires a homogeneous interface provided by a federated schema. Such a federated schema should correctly reflect the semantics of the component schemata of which it is composed. Since the semantics of a database schema is also determined by a set of semantic integrity constraints, a correct schema integration has to deal with integrity constraints existing in the different component schemata. Traditionally, most schema integration approaches solely concentrate on the structural integration of given database schemata. Local integrity constraints are often simply neglected. Their relationship to global extensional assertions, which form the basic integration constraints, are even ignored completely. In this paper, we discuss the impact of global extensional assertions and local integrity constraints on federated schemata. In particular, we point out the correspondence between local integrity constraints and global extensional assertions. The knowledge about the correspondences between the given integrity constraints and extensional assertions can then be utilized for an augmented schema integration process.     

Identifying object isomerism in multidatabase systems

In a multidatabase system that consists of object databases, the same real-world entity can be stored as objects in different databases with incompatible object identifiers. How to identify and integrate these objects representing the same entities such that (a) object duplication in the query result can be avoided, (b) information for the entity can be gathered, and (c) the specialization of multiple classes can be built is an important issue to provide a well structured global object schema and a more informative query result. In this paper, we extend our results on probabilistic query processing and joining relations on incompatible keys to solve the problem. Various data and schema conflicts such as missing data, inconsistent data and domain mismatch which may exist in classes from different databases are considered in the process of identification.Recommended by: Amit Sheth     

数据源集成系统中动态字典构造方法研究

本文从异构数据源集成系统的角度出发,引入模板和动态字典的概念,统一描述各种数据源数据的模式。动态字典不仅能描述对象的结构特征,还能描述对象的行为特征,完全符合面向对象特点。除此以外,本文还引入五种模板操作的定义,并证明ＯＩＭ对象操作的模板可由相应的模板操作构成,从而给出不通过扫描数据库,而是利用局部动态字典的模板操作构造集成系统全局动态字典的方法。     

多XML数据源的语义集成与查询处理

提出一种多XML数据源的语义集成和查询处理的途径,通过一定步骤将各个局部DTD模式集成为全局模式,同时生成全局模式到局部模式的映射。在查询处理中,查询被表示成查询树的形式,引入了补查询和连接子等概念,给出了查询分解和执行的具体算法,并首次提出并分析了XML集成环境下产生不确定查询结果的情况。     

Object-oriented query language access to relational databases: A semantic framework for query translation

This research investigates and approach to query processing in a multidatabase system that uses an objectoriented model to capture the semantics of other data models. The object-oriented model is used to construct a global schema, defining an integrated view of the different schemas in the environment. The model is also used as a self-describing model to build a meta-database for storing information about the global schema. A unique aspect of this work is that the object-oriented model is used to describe the different data models of the multidatabase environment, thereby extending the meta database with semantic information about the local schemas. With the global and local schemas all represented in an object-oriented form, structural mappings between the global schema and each local schema are then easily supported. An object algebra then provides a query language for expressing global queries, using the structural mappings to translate object algebra queries into SQL queries over local relational schema. The advantage of using an object algebra is that the object-oriented database can be viewed as a blackboard for temporary storage of local data and for establishing relationships between different databases. The object algebra can be used to directly retrieve temporarily-stored data from the object-oriented database or to transparently retrieve data from local sources using the translation process described in this paper.     

Schema design and mapping strategies for persistent object models

A formal model is presented for a conceptual schema of persistent object models that support a strong notion of object identity. The object constructors in the model are sets, tuples, and disjunct. The databases that correspond to such schemata are graph-structured object spaces. These conceptual object spaces are mapped onto physical object spaces, which are typically forests of trees. The characteristics of the physical schemata are discussed and an algorithm to transform a conceptual schema into a physical schema is given.     

Attribute equivalence in global schema design for heterogeneous distributed databases

A global schema is a single, connected view of heterogeneous databases. Past research into the problem of global schema design has demonstrated the use of generalization for connecting disjoint schemas. Before generalization can be applied, the common attributes of the local schemas must be identified. We use the term attribute equivalence for the identification of such common attributes. This paper defines four types of attribute equivalences. The distinction between local and global equivalence is explained, and special attention is given to key attributes. We also discuss the placement of locally equivalent attributes in a global schema.     

A Methodology for Structural Conflict Resolution in the Integration of Entity-Relationship Schemas

The integration ofinf ormation systems is becoming increasingly important. A common requirement in distributed data-intensive applications, such as data warehousing and data mining, is that the various databases involved be joined in a process called schema integration. The entity-relationship (ER) model or a variant of the ER model is often used as the common data model. To aid the schema conforming, merging and restructuring phases of the integration process, various transformations have been defined to map between various equivalent ER representations. In this paper, we describe a different approach to integrate ER schemas. We focus on the resolution of structural conflicts, that is, when related real-world concepts are modeled using different constructs in different schemas. Unlike previous work, our approach proposes to resolve the structural conflict between an entity type in one schema and an attribute in another schema and show that the other structural conflicts are automatically resolved. This reduces the manual effort required in integration. We give a detailed algorithm to transform an attribute in one schema into an equivalent entity type in another schema without any loss of semantics, that is, our transformation is both information preserving and constraint preserving.     

结构工程语义网格本体模型框架的设计与实现

针对结构工程领域中信息集成与共享时碰到的语义冲突问题,基于网格计算和语义Web的相关技术规范,设计和实现结构工程语义网格体系结构.并在此基础上,着重分析在构建结构工程语义网格语义层的过程中,在实例集成、模式集成、概念集成和查询应用几个阶段的语义冲突问题,设计与初步实现语义层本体模型框架.     

Efficient query processing in integrated multiple object databaseswith maybe result certification

Within integrated multiple object databases, missing data occurs due to the missing attribute conflict as well as the existence of null values. A set of algorithms is provided in this paper to process the predicates of global queries with missing data. To provide more informative answers to users, the "maybe" results due to missing data are presented in addition to the "certain" results. The local "maybe" results may become "certain" results via the concept of object isomerism. One algorithm is designed based on the centralized approach in which data are forwarded to the same site for integration and processing. Furthermore, to reduce the response time, localized approaches evaluate the predicates within distinct component databases in parallel. The object signature is also applied in the design to further reduce the data transfer. These algorithms are compared and discussed according to the simulation results of both the total execution and response times. Alternately, the global schema may contain multi-valued attributes with values derived from attribute values in different component databases. Hence, the proposed approaches are also extended to process the global queries involving this kind of multi-valued attribute     

基于元数据的分布异构数据集成研究

将“虚拟法”和“数据仓库法”结合,通过统一的数据交换中心解决数字气田分布异构数据集成问题。建立包含全局模式和全局-局部映射的元数据字典,屏蔽异构数据细节,由此解决异构数据的各种冲突。提出一种由分布数据源的局部模式归并建立全局模式和映射表的算法,以提高模式集成的自动能力。     

基于本体的关系数据集成的查询处理

为实现异构关系数据库的语义集成,针对传统集成技术存在的问题,在对语义网等相关技术进行分析的基础上,研究基于本体的关系数据集成系统中的查询处理问题,提出了一种基于本体的关系数据库集成框架。设计了基于本体的关系数据的描述方法,使用本体作为集成的全局模式来描述关系模式的语义。设计了查询重写算法,该算法可以将基于全局模式的SPARQL查询重写为针对具体关系数据库的查询,从而实现对异构关系数据库的集成。实验表明,该算法具有良好的可扩展性。     

Semantic schema refinements for multilevel schema integration

Within the database field, schema refinements have been proved useful for documentation and maintenance purposes; moreover, schemata describing the reality of interest at different levels of abstraction are extensively used in Computer Aided Software Engineering tools and visual query languages. So, much effort has been spent in analyzing schema transformations and schema refinements. Till now, however, while the syntaxof schema transformations has been deeply investigated, the semantics has been very often neglected. In this paper we present a full formal framework, supporting both the syntax and the semantics of schema refinements. Such a formal framework is used to support a methodology able to merge a set of schemata and the top-down chains of refinement planes produced during their design. The result of this kind of integration, that we call multilevel integration, is an integrated schema plus an associated top-down chain of schemata. The integrated schema and the chain are related to the input schemata by interesting properties, giving rise to a two-dimensional structure useful for exploring the data content of complex information systems.     

CIMS环境下基于对象的信息集成框架

信息集成是实现ＣＩＭＳ的关键．文中在集成模型的选择和集成系统的设计上引入了面向对象的思想，提出了一个基于对象的信息集成框架，并着重讨论了本地对象模式和全局对象模式设计和实现的关键技术．与传统的信息集成方法相比，基于对象的信息集成技术能更自然地表达已有数据库之间的语义信息，并保持已有应用程序的独立性，而且具有良好的可扩充性．