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.     

Reducing the search space for conceptual schema transformation

In this paper we focus on the transformation of a conceptual schema into an internal schema. For a given conceptual schema, quite a number of internal schemata can be derived. This number can be reduced by imposing restrictions on internal schemata.

We present a transformation algorithm that can generate internal schemata of several types (including the relational model and the NF² model). Guidance parameters are used to impose further restrictions.

We harmonise the different types of schemata by extending the conceptual language, such that both the conceptual and the internal models can be represented within the same language.     

A methodology for integration of heterogeneous databases

The transformation of existing local databases to meet diverse application needs at the global level is performed through a four-layered procedure that stresses total schema integration and virtual integration of local databases. The proposed methodology covers both schema integration and database integration, and uses a four-layered schema architecture (local schemata, local object schemata, global schema, and global view schemata) with each layer presenting an integrated view of the concepts that characterize the layer below. Mechanisms for accomplishing this objective are presented in theoretical terms, along with a running example. Object equivalence classes, property equivalence classes, and other related concepts are discussed in the context of logical integration of heterogeneous schemata, while object instance equivalence classes and property instance equivalence classes, and other related concepts are discussed for data integration purposes. The proposed methodology resolves naming conflicts, scaling conflicts, type conflicts, and level of abstraction, and other types of conflicts during schema integration, and data inconsistencies during data integration     

A model-driven approach to semi-structured database design

Recently XML has become a standard for data representation and the preferred method of encoding structured data for exchange over the Internet. Moreover it is frequently used as a logical format to store structured and semi-structured data in databases. We propose a model-driven and configurable approach for modeling hierarchical XML data using object role modeling (ORM) as a flat conceptual model. First a non-hierarchical conceptual schema of the problem domain is built using ORM and then different hierarchical views of the conceptual schema or parts of it are specified by the designer using transformation rules. A hierarchical modeling notation called H-ORM is proposed to show these hierarchical views and model more complex semi-structured data constructs and constraints. We also propose an algorithm to map hierarchical H-ORM views to XML schema language.     

A case study in mapping conceptual designs to object‐relational schemas

The recent emergence of object‐relational technology into the commercial database market has caused new challenges for the implementation of conceptual database designs. This paper presents our experience with using the Oracle 8 object‐relational data model in the implementation of an engineering application described using the EXPRESS conceptual modeling language. EXPRESS is part of the engineering community's Standard for the Exchange of Product Data and can be characterized as a structurally object‐oriented modeling language, supporting the notion of entities, entity hierarchies, complex constraints on entity hierarchies, relationships and inverse relationships between entities, and user‐defined types. As a result, EXPRESS provides an excellent framework for studying the mapping of conceptual modeling concepts into an object‐relational model. In this paper, we describe the way in which the features of EXPRESS can be mapped into object‐relational features such as object tables, object references, and nested tables. We also describe the manner in which features such as member functions on object types, triggers, and stored procedures can be used to support the implementation of constraints associated with a conceptual schema. Although the mappings presented are specific to EXPRESS and Oracle 8, the mappings are generalizable to conceptual modeling languages and object‐relational models with similar features. Our work defines how traditional mapping concepts must be revised in order to make adequate use of the features now found in object‐relational models. As part of this paper, we also compare our mapping approach using Oracle 8 to mapping issues for the PostgreSQL object‐relational model and the Objectivity/DB object‐oriented data model. Copyright © 2000 John Wiley & Sons, Ltd.     

Deriving static and dynamic concepts from software requirements using sophisticated tagging

Natural language requirements specifications form the basis for the subsequent phase of the information system development process, namely the development of conceptual schemata. Both, the textual as well as the conceptual representations are not really appropriate for being thoroughly captured and validated by the ‘requirement holders’, i.e. the end users. Therefore, in our approach the textual specifications are firstly linguistically analyzed and translated into a so-called conceptual predesign schema. That schema is formulated using an interlingua which is based on a lean semantic model, thus allowing users to participate more efficiently in the design and validation process. After validation, the predesign schema is mapped to a conceptual representation (e.g. UML). The sequence of these translation and transformation steps is described by the “NIBA workflow”. This paper focuses on the information supporting a step by step mapping of natural language requirements specifications to a conceptual model, and on how that information is gained. On particular, we present a four-level interpretation of tagging-output.     

Tools for designing conceptual schemata of databases

CSDL, a language for designing conceptual schemata, is described. The language provides tools to ease the translation of knowledge about data into a formal conceptual schema.     

CSDL: A Conceptual Schema Definition Language for the Design of Data Base Applications

A language to support the incremental design of the conceptual schemata of data bases is presented. Abstractions are expressed in terms of high-evel constructs and operations on these abstractions allow the definition of other abstractions. Both abstractions and operations on them are totally independent from the underlying internal representation of the schema, which is created consistently by applying the operators of the language. In addition, the language offers a. number of support facilities for type checking of relationships and graphical displays of the conceptual schemata for easier understanding.     

Semantic hierarchies and abstractions in conceptual schemata

A conceptual schema is a clear, easy to understand and exact representation of the semantics of an underlying universe of discourse. The role of such schemata in the specification and design of information bases is now widely recognized. However, in “real life” applications, it is often the case that the size of the conceptual schema exceeds the limit above which it is necessary to have an abstraction mechanism available, as otherwise it would become difficult to understand.In this paper, we present several concepts and heuristic procedures which allow for semantic modularization of a conceptual schema, thus providing a concise representation, using different degrees of abstraction and/or viewpoints, of a schema of any size.     

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     

Defining views in the Binary Relationship Model

The Binary Relationship Model has been praised for the way it not only supports, but practically forces us to model the “deep structures” of the information in the conceptual schema. An adverse effect is that the conceptual schema becomes very large. This, combined with the fact that a Binary Relationship Model schema gives a “flat” representation of the information, makes it very hard to distinguish important concepts of a model from its less important details. Furthermore, the length of DML statements is directly proportional to the size of the schema. What we need for practical applications is a way of keeping the “deep structures” while seeing only the “surface structures”. We need to be able to define views on a conceptual schema. We need to be able to select and derive from the conceptual schema precisely the concepts we are interested in for each application of our model.We propose two new concepts for view definition in the Binary Relationship Model, DOTs and shortcuts. DOTs are dervied object types and shortcuts are derived roles which are used in the definition of derived binary relationship types.     

A conceptual schema-based temporal meta database schemas generation technique for 3D objects

In this paper, a temporal meta database for three-dimensional (3D) objects whose properties and relationships are supported by valid time is introduced. Based on our proposed temporal object-oriented conceptual schema model, a conceptual schema of the temporal meta database can be generated from a 3D graphical data source and other particular application requirements. Based on our proposed temporal object relational data model with attribute timestamping, logical schemas of the temporal meta database can be systematically and automatically generated from the conceptual schema. From the temporal meta database, non-temporal/temporal metadata about temporal 3D objects are available for temporal information system users. Convenient access using database languages such as SQL can be performed. Queries over 3D objects using a temporal object relational SQL are demonstrated.     

信息集成系统中的模式融合问题研究

将模式融合分为模式映射、主键-外键融合和用户自定义的完整性融合3个部分。模式映射将关系模式或其他模式映射为对象代理模式类,主键-外键映射采用新的模式融合算法,充分考虑对象代理模型的特点。提出了一个新的操作Merge来解决用户自定义的模式融合。该操作克服了其他模型的用户自定义模式限制难于融合的问题。在Smalltalk环境中实现了基于对象代理模型的模式融合系统,并给出应用实例。     

搜索问题的代数描述及其算法

文中给出了搜索问题的一种代数描述方法，在这种描述方法的基础上，给出了一个算法模式。以货郎担问题的动态规划－分支限界法为例，讨论了如何用所给出的算法模式来设计饱含多咱算法设计技术的算法，称这种算法为混合（ｈｙｂｒｉｄ）算法。还讨论了如何用面向对象的方法进行程序设计。这种求解问题的方法不仅为算法的自支生成提供了一种有力的工具，如果用面向对象的方法进行程序设计，还能提高代码的利用率。     

An Object Algebra Approach to Multidatabase Query Decomposition in Donají

This paper presents an approach to query decomposition in a multidatabase environment. The unique aspect of this approach is that it is based on performing transformations over an object algebra that can be used as the basis for a global query language. In the paper, we first present our multidatabase environment and semantic framework, where a global conceptual schema based on the Object Data Management Group standard encompasses the information from heterogeneous data sources that include relational databases as well as object-oriented databases and flat file sources. The meta-data about the global schema is enhanced with information about virtual classes as well as virtual relationships and inheritance hierarchies that exist between multiple sources. The AQUA object algebra is used as the formal foundation for manipulation of the query expression over the multidatabase. AQUA is enhanced with distribution operators for dealing with data distribution issues. During query decomposition we perform an extensive analysis of traversals for path expressions that involve virtual relationships and hierarchies for access to several heterogeneous sources. The distribution operators defined in algebraic terms enhance the global algebra expression with semantic information about the structure, distribution, and localization of the data sources relevant to the solution of the query. By using an object algebra as the basis for query processing, we are able to define algebraic transformations and exploit rewriting techniques during the decomposition phase. Our use of an object algebra also provides a formal and uniform representation for dealing with an object-oriented approach to multidatabase query processing. As part of our query processing discussion, we include an overview of a global object identification approach for relating semantically equivalent objects from diverse data sources, illustrating how knowledge about global object identity is used in the decomposition and assembly processes.     

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.     

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．     

Schema evolution of an object-oriented real-time database systemfor manufacturing automation

Database schemata often experience considerable changes during the development and initial use phases of database systems for advanced applications such as manufacturing automation and computer-aided design. An automated schema evolution system can significantly reduce the amount of effort and potential errors related to schema changes. Although schema evolution for nonreal-time databases was the subject of previous research, its impact on real-time database systems remains unexplored. These advanced applications typically utilize object-oriented data models to handle complex data types. However, there exists no agreed-upon real-time object-oriented data model that can be used as a foundation to define a schema-evolution framework. Therefore, the authors first design a conceptual real-time object-oriented data model, called Real-time Object Model with Performance Polymorphism (ROMPP). It captures the key characteristics of real-time applications-namely, timing constraints and performance polymorphism-by utilizing specialization-dimension and letter-class hierarchy constructs, respectively. They then re-evaluate previous (nonreal-time) schema evolution support in the context of real-time databases. This results in modifications to the semantics of schema changes and to the needs of schema change resolution rules and schema invariants. Furthermore, they expand the schema change framework with new constructs-including new schema change operators, new resolution rules, and new invariants-necessary for handling the real-time characteristics of ROMPP