Manuel García-Solaco

Suitability of datamodels 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.nSeveral data models are analyzed with repect to the characteristics of the framework, to evaluate their adequacy as canonical models.

Overcoming Schematic Discrepancies in Interoperable Databases

Abstract 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.

Semantically Enriching Relational Databases into an Object Oriented Semantic Model

A method to convert relational schemas to an object oriented semantic model is presented. It makes explicit knowledge about the semantic of the database that was implicit in the schemas or in the extension, through a knowledge acquisition phase. The method is general, semiautomatic, and has a number of applications.

Discovering interdatabase resemblance of classes for interoperable databases

The integration of database schemas into a federated one involves a detection phase where the similarities that exist among the classes of the different databases must be discovered in order to determine their semantic relationships. This phase is typically characterized by the complexity of the comparison task and the deep knowledge about the semantics of the databases that is required to perform it. The authors present an approach to handle this problem by upgrading the semantic level of the local schemas and guiding the search of the comparison process by the structure of the generalization/specialization semilattices and aggregation graphs of the resulting rich schemas. Unnecessary as well as most promising comparisons are identified and a systematic procedure to analyze the rich component schemas in a meaningful way is given. A reduction of the complexity is achieved. The methodology serves as the basis for a tool that semiautomatizes the process. The expressiveness of the canonical model plays a central role.<<ETX>>

Discriminated operations for interoperable databases

Federation Rules to be followed when associating external schemas into federated schemas are formulated. Discriminated operations in an object oriented model, such as discriminated generalization, and in the relational model, such as discriminated union and outer union, are introduced. It is then shown how they may help in obeying the Federation Rules. These operations allow multiple semantics in a single federated schema and thence minimize the number of federated schema needed, as well as their maintenance. They also allow easier solutions to other problems.<<ETX>>

Extensional issues in schema integration

To form a Cooperative Information System in which several pre-existing 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.