Database schema

Résumé

The database schema is the structure of a database described in a formal language supported typically by a relational database management system (RDBMS). The term "schema" refers to the organization of data as a blueprint of how the database is constructed (divided into database tables in the case of relational databases). The formal definition of a database schema is a set of formulas (sentences) called integrity constraints imposed on a database. These integrity constraints ensure compatibility between parts of the schema. All constraints are expressible in the same language. A database can be considered a structure in realization of the database language. The states of a created conceptual schema are transformed into an explicit mapping, the database schema. This describes how real-world entities are modeled in the database. "A database schema specifies, based on the database administrator's knowledge of possible applications, the facts that can enter the dat

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https://en.wikipedia.org/wiki/Database_schema

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Predictive approach for schema evolution

Hassina Bounif

In today's companies and organizations, databases are omnipresent. They are the means to represent and store information. Therefore, they must evolve whenever the information architecture (semantic and structure) changes. Databases are subject to evolution for several reasons that include the changes to the real-world or the emergence of new database user requirements. We may also consider non representational and non-functional aspects such as the technology and performance requirements. Those can also compel the database designer or administrator to change the database in order to be more optimal and adapted to those requirements. This thesis proposes to address the schema evolution problem by anticipating the potential changes for the evolution of the schema. The approach adopts the a priori perspective i.e. to plan in advance for a possible solution that makes a schema evolve over time. Such a solution works with both a set of assumptions and techniques. The elaborated approach is based on different components: • First, we propose to develop a schema repository which contains a wide number of heterogeneous schemas and their historical versions. This repository serves in a series of operations that are important for the study of the schemas such as selecting the pertinent schemas, building the change matrices and performing the data-mining process. • Second, we propose to develop a requirements ontology, meaning to say a domain ontology that describes the current concepts of a database as well as the concepts that represent the potential future requirements that could be part of the evolution. The method of construction of this ontology includes several phases such as the preparation of the data for this ontology, the establishment of the data-dictionary besides change perspectives that store the concepts that are associated to other concepts by relationships resulting from the application of the data-mining process, the evaluation of the domain ontology using a graph structure and finally the construction of the ontology using a set of procedures. • Third, we propose to develop a predicted schema which is a database schema that contains two types of metadata. The metadata, that represents current entities of the database and the metadata that represents potential future entities. The predicted schema has two methods of representation: the multi-representation strategy and the predicted design repository schemas strategy. The schemas with the multi-representation strategy are particular versions of schemas whereas the schemas with the predicted design repository schemas are particular repositories of schemas. • Finally, we propose a case study and an analysis of the approach. The case study to better understand how this approach works and the analysis to show its feasibility, the positive as well as negative aspects.

EPFL2009

Chargement

Predictive Approach for Database Schema Evolution

Hassina Bounif

Information systems, including their core databases need to meet changing user requirements and adhere to evolving business strategies. Traditional database evolution techniques focus on reacting to change to smoothly perform schema evolution operations and to propagate corresponding updates to the data as effectively as possible. Adopting such posterior solutions to such changes generates high costs in human resources and financial support. We advocate an alternate solution: a predictive approach to database evolution. In this approach, we anticipate future changes during the standard requirements analysis phase of schema development. Our approach enables potential future requirements to be planned for, as well as the standard, determining what data is to be stored and what access is required. This preparation contributes significantly in the ability of the database schema to adapt to future changes and to estimate their relative costs.

Idea Group2006

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Schema matching is the process of establishing correspondences between the attributes of database schemas for data integration purpose. Although several schema matching tools have been developed, their results are often incomplete or erroneous. To obtain correct attribute correspondences, in practice, human experts edit the mapping results and fix the mapping problems. As the scale and complexity of data integration tasks have increased dramatically in recent years, the reconciliation phase becomes more and more a bottleneck. Moreover, one often needs to establish the correspondences in not only between two but a network of schemas simultaneously. In such reconciliation settings, it is desirable to involve several experts. In this paper, we propose a tool that supports a group of experts to collaboratively reconcile a set of matched correspondences. The experts might have conflicting views whether a given correspondence is correct or not. As one expects global consistency conditions in the network, the conflict resolution might require discussion and negotiation among the experts to resolve such disagreements. We have developed techniques and a tool that allow approaching this reconciliation phase in a systematic way. We represent the expert's views as arguments to enable formal reasoning on the assertions of the experts. We detect complex dependencies in their arguments, guide and present them the possible consequences of their decisions. These techniques thus can greatly help them to overlook the complex cases and work more effectively.

2013

Chargement

Predictive approach for schema evolution

Hassina Bounif

EPFL2009