Due to the development of the World Wide Web, the integration of heterogeneous data sources has become a major concern of the database community. Appropriate architectures and query languages have been proposed. Yet, the problem of data conversion which is essential for the development of mediators/wrappers architectures has remained largely unexplored. In this paper, we present the YAT system for data conversion. This system provides tools for the specification and the implementation of data conversions among heterogeneous data sources. It relies on a middleware model, a declarative language, a customization mechanism and a graphical interface. The model is based on named trees with ordered and labeled nodes. Like semistructured data models, it is simple enough to facilitate the representation of any data. Its main originality is that it allows to reason at various levels of representation. The YAT conversion language (called YATL) is declarative, rule-based and features enhanced patt...

this report, we examine the technical challenges to integration, critique the available tools and resources, and compare the cost and advantages of various methodologies. We begin by analyzing the basic steps in strict and complete integration: 1) transformation of the various schemas to a common data model; 2) matching of semantically related schema objects; 3) schema integration; 4) transformation of data to the federated database on demand; and 5) matching of semantically equivalent data. Some progress has been made on generic problems such as (1) and (3) within the wider database community, but issues of semantics (steps (2) and (5)) have only been dealt with any degree of success by domain experts within the biological community. We then look at the solution space of integration strategies as defined by two axes, the "tightness" of federation and the "degree" of instantiation, discuss where various solutions fall on this plane, and examine their cost and advantages/disadvantages. Finally, we examine technical challenges that are not -3- July 12, 1995

Current theoretical work offers measures of schema equivalence based on the information capacity of schemas. This work is based on the existence of abstract functions satisfying various restrictions between the sets of all instances of two schemas. In considering schemas that arise in practice, however, it is not clear how to reason about the existence of such abstract functions. Further, these notions of equivalence tend to be too liberal in that schemas are often considered equivalent when a practitioner would consider them to be different. As a result, practical integration methodologies have not utilized this theoretical foundation and most of them have relied on ad-hoc approaches. We present results that seek to bridge this gap. First, we consider the problem of deciding information capacity equivalence and dominance of schemas that occur in practice, i.e., those that can express inheritance and simple integrity constraints. We show that this problem is undecidable. This undecidab...

. We describe the development of a tool, called MDM, for the management of multiple models and the translation of database schemes. This tool can be at the basis of an integrated CASE environment, supporting the analysis and design of information systems, that allows different representations for the same data schemes. We first present a graphtheoretic framework that allows us to formally investigate desirable properties of schema translations. The formalism is based on a classification of the constructs used in the known data model into a limited set of types. Then, on the basis of formal results, we develop general methodologies for deriving "good" translations between schemes and, more in general, between models. Finally, we define the architecture and the functionalities of a first prototype that implements the various features of the approach. 1 Introduction During the past decade, the availability and use of automated tools for the analysis and development of information systems...

We present an approach to determine the similarity of classes which utilizes fuzzy and incomplete terminological knowledge together with schema knowledge. We clearly distinguish between semantic similarity determining the degree of resemblance according to real world semantics, and structural correspondence explaining how classes can actually be interrelated. To compute the semantic similarity we introduce the notion of semantic relevance and apply fuzzy set theory to reason about both terminological knowledge and schema knowledge. 1 Introduction The identification of similar or corresponding concepts forms one of the main steps when investigating different world models and relating them to each other. Apart from its long tradition in document retrieval, this issue has also been investigated in more structured frameworks such as schema independent query formulation, e.g., [Mot90], or database integration, where for a survey you may look at [SL90]. As argued in [GPN91], there should b...

The need to transform data between heterogeneous databases arises from a number of critical tasks in data management. These tasks are complicated by schema evolution in the underlying databases, and by the presence of non-standard database constraints. We describe a declarative language, WOL, for specifying such transformations, and its implementation in a system called Morphase. WOL is designed to allow transformations between the complex data structures which arise in object-oriented databases as well as in complex relational databases, and to allow for reasoning about the interactions between database transformations and constraints. integrating the US Cities-and-States and European-Citiesand-Countries databases shown in Figures 1 and 2. The graphical notation used here is inspired by [2]: the boxes represent classes which are finite sets of objects; the arrows represent attributes, or functions on classes. name str

The contributions of this paper are two-fold: First we introduce a novel, axiomatically defined, object-oriented data model, called the Demeter kernel model, and second we present abstraction and optimization algorithms and their relationships for designing classes from objects in the kernel model. We analyze several computational problems underlying the class design process which is divided into two phases: a learning phase and an optimization phase. This study focuses on approximation algorithms for the optimization phase and leads to a better understanding and a partial automation of the object-oriented design process. The algorithms and the theory presented in this paper have been implemented in the C++ Demeter System TM , a CASE tool for object-oriented design and programming. Keywords: Object-oriented programming and design, reverse engineering, formal software engineering techniques, class hierarchy optimization. Acknowledgements: Preliminary versions of this paper ...

In this paper we study the problem of translating schemes between different data models, in a formal framework that refers to a wide range of models. We first introduce a graphtheoretic formalism that allows us to uniformly represent schemes and models, to compare different data models and to describe the behavior of basic translations. The formalism is based on a classification of the constructs used in the known data model into a limited set of types. Then, we study in this framework formal properties of scheme translation between heterogeneous data models, and we develop a method for deriving translations that enjoy those properties. Keywords Data models, Metamodel, Heterogeneity, Schema translation, Lattice structure. 1 INTRODUCTION 1.1 Motivations and background It is widely accepted now that a conceptual data model be used in the analysis phase and many tools exist that support the analysis and design of information systems (see for instance the book of Batini et al. (1992))...

Abstract. Database transformations arise in many di erent settings including database integration, evolution of database systems, and implementing user views and data-entry tools. This paper surveys approaches that have beentaken to problems in these settings, assesses their strengths and weaknesses, and develops requirements on a formal model for specifying and implementing database transformations. We also consider the problem of insuring the correctness of database transformations. In particular, we demonstrate that the usefulness of correctness conditions such as information preservation is hindered by theinteractions of transformations and database constraints, and the limited expressive power of established database constraint languages. We conclude that more general notions of correctness are required, and that there is a need for a uniform formalism for expressing both database transformations and constraints, and reasoning about their interactions. Finally we introduce WOL, a declarative language for specifying and implementing database transformations and constraints. We brie y describe the WOL language and its semantics, and argue that it addresses many of the requirements on a formalism for dealing with general database transformations. 1

ii Class organizations (schemas) evolve over the life cycle of object-oriented systems for avariety of reasons. This issue has recently been a subject of increasing attention in the literature of both object-oriented languages and object-oriented database systems. One of the most common forms of evolution involves the extension of an existing system by addition of new classes of objects or the addition of attributes to the original objects. Sometimes class structures are reorganized even when the set of objects is unchanged. In this case the reorganization might represent an optimization of the system, or just a change in the users ' perspective. At the other extreme, a class reorganization might re ect not only the extension and reclassi cation of existing objects, but also structural changes (other than addition of attributes) in the original objects. This work provides a mathematical treatment of a calculus of class transformations. Three kinds of transformations that commonly occur in the evolution of class structures are considered: object-extending, object-preserving, and language-preserving. For each kind of transformation, methods for automating the maintenance of systems based on the evolving class structure are discussed. The language-preserving transformations are a special case of transformations that change the structure of existing objects. If an object schema is decorated with concrete syntax, it de nes not only a class structure, but also a language for describing the objects. When two schemas de ne the same language but di erent classes, the language may be used to guide the discovery of analogies between the classes. The resulting analogies may then be used to transport functionality between domains. iii Acknowledgments Iwould like to thank my advisor, Karl Lieberherr, for his generous support, guidance, and feedback. I would also like to thank my wife, Vickie, for her constant encouragement and understanding without which thiswork would not have been possible. iv