DIVERSITY WITH COOPERATION IN DATABASE SCHEMATA: SEMANTIC RELATIVISM

Diversity is an asset, as long as it allows cooperation. In the case of information systems and databases, the data model used is a help or a hindrance for this cooperation of diverse views; this is characterized by the semantic relativism of the model. We first analyze diversity within an information system, where cooperation is made possible by the use of external schemata; semantic relativism of the model of the database schema is the key f,ictor. Then we discuss diversity between different information systenis, where they cooperate through interoperability, by schema integration into federated schemata; semantic relativism of the canonical data model is shown to be determinant

Managing polyglot systems metadata with hypergraphs

A single type of data store can hardly fulfill every end-user requirements in the NoSQL world. Therefore, polyglot systems use different types of NoSQL datastores in combination. However, the heterogeneity of the data storage models makes managing the metadata a complex task in such systems, with only a handful of research carried out to address this. In this paper, we propose a hypergraph-based approach for representing the catalog of metadata in a polyglot system. Taking an existing common programming interface to NoSQL systems, we extend and formalize it as hypergraphs for managing metadata. Then, we define design constraints and query transformation rules for three representative data store types. Furthermore, we propose a simple query rewriting algorithm using the catalog itself for these data store types and provide a prototype implementation. Finally, we show the feasibility of our approach on a use case of an existing polyglot system.Peer ReviewedPostprint (author's final draft

Semantics of Database Transformations

Database transformations arise in many different settings including database integration, evolution of database systems, and implementing user views and data entry tools. This paper surveys approaches that have been taken to problems in these settings, assesses their strengths and weaknesses, and develops require ments 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 the interactions 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 briefly 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

Overcoming Schematic Discrepancies in Interoperable Databases

An important kind of semantic conflicts arising in database interoperability are schematic discrepancies, where data in one database correspond to metadata in another. We present a general solution to these discrepancies, based on a framework of two dimensions: generalization and aggregation. Operations to transform metadata into data and vice versa are defined, in the relational model and in an object-oriented model. These operations may be applied at different levels in a federated architecture. Keyword Codes: H.2.5 Keywords: Heterogeneous Databases 1. INTRODUCTION The cooperation between autonomous and already existing databases in order to share their data while at the same time maintaining their autonomy has given rise to a new kind of distributed database architecture called Interoperable or Federated Database Systems [1] (FDBS). Heterogeneity is one of their features and is an effect of their design and organization autonomies. On one side, we have a syntactic heterogeneity tha..

Suitability of Data Models as Canonical Models for Federated Databases

We develop a framework of characteristics, essential and recommended, that a data model should have to be suitable as canonical model for federated databases. This framework is based on the two factors of the representation ability of a model: expressiveness and semantic relativism. Several data models are analyzed with respect to the characteristics of the framework, to evaluate their adequacy as canonical models. 1 Introduction When several databases (DBs) are to interoperate, they form a federation, and a data model must be chosen as the canonical data model (CDM) for the federation (we use the terminology of [SL90]). Work on federated or interoperable databases has often used an Entity Relationship (ER) model, or some extension of it, as the CDM; others have adopted an Object Oriented (OO) model. Is any data model equally adequate as CDM? This paper discusses some characteristics of a data model that make it suitable as the CDM of a federation. Note that we are not trying to une..

Extensional Issues in Schema Integration

To form a Cooperative Information System in which several preexisting information systems cooperate by means of database interoperability, a methodology for database schema integration is needed. Extensional issues should be taken into account in such a methodology. We show how objects in different databases that represent the same real world object may be correlated through an object identification function (oif), and collapsed in external classes, when there are no dependencies between the component databases. We also extend our methodology to deal with those cases in which, in addition to this oif, existence interdependencies are to be specified and enforced. The powerful abstractions of our BLOOM model are used in both cases. 1. Introduction The cooperation between several information systems (ISs) may arise in a number of cases. Different organizations, each with its own IS, may want to cooperate (subsidiaries of a common parent company, states of a federal country, government ag..

Diversity with cooperation in database schemata: Semantic relativism

Diversity is an asset, as long as it allows cooperation. In the case of information systems and databases, the data model used is a help or a hindrance for this cooperation of diverse views; this is characterized by the semantic relativism of the model. We first analyze diversity within an information system, where cooperation is made possible by the use of external schemata; semantic relativism of the model of the database schema is the key factor. Then we discuss diversity between different information systems, where they cooperate thru interoperability, by schema integration into federated schemata; semantic relativism of the canonical data model is shown to be determinant. 1. Introduction Different people have diverse views of reality; they perceive and conceptualize the same portion of reality in diverse ways. We find not an absolute view, only relative views. Is this diversity good or bad? If it is an impediment for their cooperation, it is bad. The remedy is not uniformity, t..