In this paper, we carefully explore the assumptions behind using information capacity equivalence as a measure of correctness for judging transformed schemas in schema integration and translation methodologies. We present a classification of common integration and translation tasks based on their operational goals and derive from them the relative information capacity requirements of the original and transformed schemas. We show that for many tasks, information capacity equivalence of the schemas is not strictly required. Based on this, we present a new definition of correctness that reflects each undertaken task. We then examine existing methodologies and show how anomalies can arise when using those that do not meet the proposed correctness criteria. 1 Introduction Formal work on schema equivalence has largely been ignored within practical schema integration and translation tools. Practitioners have felt that theoretical work is too narrow in scope to be applicable to the problems ...

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...

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

The process of software development is gradually achieving more rigor. Proficient developers now construct software indirectly through the abstraction of models. Models allow a developer to focus on the essential aspects of an application and defer details. Transformations extend the power of models, as the developer can substitute refinement and optimization of models for tedious manipulation of code. This paper catalogs object modeling transformations that we have encountered in our application work. 1.

The paper describes the architectural principles of a database CASE tool that allows more flexible design strategies than those of traditional tools that propose oversimplistic draw-and-generate approaches. Providing this flexibility is based on four basic principles, namely a unique generic specification model that allows the definition of a large variety of specific design products, transformational functions as major database design tools, a toolbox architecture, allowing a maximal independence between functions, and multiple model definition through parametrization of the unique generic model. These architectural characteristics themselves derive from two fundamental paradigms, namely the process-product-requirements approach to model design behaviours, and the transformational approach to system design. Keywords : design modeling, system design, database design, transformational approach, CASE tools. 1.

logical structures. This relational schema is an approximate translation of the schema of Figure 2-1. The term record type must read table, field must read column and primary id must read primary key. Logical specifications A logical schema comprises data structure definitions according to one of the commonly used families of models: relational model, network model (CODASYL DBTG), hierarchical model (IMS), shallow model (TOTAL, IMAGE), inverted file model (DATACOM/DB), standard file model (COBOL, C, RPG, BASIC) or object-oriented model. For instance, the schema of Figure 2-2 can be considered as a possible relational translation the conceptual This schema defines seven logical record types. PERSON has mandatory logical fields (PID, NAME, ADD_STREET and ADD_CITY) and one optional (nullable) field, ADD_NUM. Its primary identifier is {PID}. Field {PID} of ORDER is a foreign key to CUSTOMER (targeting its primary id). The group {PID, ONUM} of DETAIL is a multicomponent foreign k...

An increasing dependence and cooperation between organisations has created a need for many enterprises to access remote as well as local information sources. Thus, it becomes important to be able to interconnect existing, heterogeneous information systems. One form of heterogeneity is semantic heterogeneity, which occurs when there is a disagreement regarding the interpretation and intended use of related information, or when the same phenomenon in a Universe of Discourse is modelled in different ways in two systems. In this paper, we survey the basic problems caused by semantic heterogeneity and suggest a number of research directions that address these problems. 1 Introduction Interoperability is becoming a critical issue for many organisations today. An increasing dependence and cooperation between organisations has created a need for many enterprises to access remote as well as local information sources. Further, even a single enterprise may have several independent information ba...

. This is an abstract of a revision of the original paper (ER'93 pre-proceedings 2 ) that presents a DBMS-independent database reverse engineering (DBRE) methodology based on a generic process model and on transformation techniques. DBRE is proposed as a twophase process consisting in recovering the DBMS-dependent data structures (data structure extraction) then in recovering their semantics (data structure conceptualization). The second phase, that is strongly linked with the logical design phase of current database design methodologies, can be performed by application of a selected set of standard schema transformations. The paper illustrates the methodology by applying it to various DBRE processes : removing optimization structures, untranslating database/file structures, and finally conceptual normalization. Keywords : database design, database reverse engineering, schema transformation, schema equivalence 1. Introduction Reverse engineering a piece of software consi...

We develop a formal data model, the Schema Intension Graph (SIG) model, to aid in understanding the relative information capacity of schemas containing constraints. The basic building blocks of the SIG model are sets that may be combined by the nested application of union and product constructors. The model also permits the expression of binary relations on sets and simple integrity constraints on these relations. We discuss the motivation used in designing the model and establish some fundamental results on the model. We consider the problem of constraint implication in the SIG model and give a sound and complete set of implication rules for a subclass of SIG schemas, called simple SIG schemas. The general constraint implication problem is shown to be undecidable. Finally, we consider information capacity preserving translations of a subclass of relational schemas with functional and inclusion dependencies into simple SIG schemas. These translations assist in determining the relative ...

Abstract. Integration of multiple heterogeneous data sources continues to be a critical problem for many application domains and a challenge for researchers world-wide. Schema matching, a fundamental aspect of integration, has been a well-studied problem. However researchers have, for the most part, concentrated on the development of different schema matching algorithms, and their performance with respect to the number of matches produced. To the best of our knowledge, current research in schema matching does not address the issue of quality of matching. We believe that quality of match is an important measure that can not only provide a basis for comparing multiple matches, but can also be used as a metric to compare as well as optimize existing match algorithms. In this paper, we define the Quality of Match (QoM) metric, and provide qualitative and quantitative analysis techniques to evaluate the QoM of two given schemata. In particular, we introduce a taxonomy of schema matches as a qualitative analysis technique, and a weight-based match model that in concert with the taxonomy provides a quantitative measure of the QoM. We show, via examples, how QoM can be used to distinguish the “goodness ” of one match in comparison with other matches.