Andrea Rodr´ ıguez Summer School - Castell´n 2004 o
Department of Computer Science University of Concepci´n, Chile o http://www.inf.udec.cl/∼andrea andrea@udec.cl
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Introduction
Information and data are different. Information is understood by a person. Data are values stored on a passive medium like a computer disk. The purpose of a database management system (DBMS) is to bridge the gap between information and data - the data stored in memory or on disk must be converted to usable information. The basic processes that are supported by a DBMS are: • Specification of data types, structures and constraints to be considered in an application. • Storing the data itself into persistent storage. • Manipulation of the database. • Querying the database to retrieve desired data • Updating the content of the database A database is a model of a real world system. The contents (sometimes called the extension) of a database represent the state of what is being modeled. Changes in the database represent events occurring in the environment that change the state of what is being modeled. It is appropriate to structure a database to mirror what it is intended to model. Databases can be analyzed at different levels: • Conceptual Modeling • Logical Modeling • Physical Modeling
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Conceptual Modeling
Conceptual-level concepts permit us to model the application world in terms that are independent of any particular data (logical) model. Conceptual models provide a framework for developing a
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database schema from the top to the bottom in the process of a database design. This Section examines the entity-relationship model and the object-oriented model as representatives of conceptual modeling. The entity-relationship model is widely used and the object-oriented model is gaining more acceptance for non-traditional databases.
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The Entity-Relationship Model
The entity-relationship model is a tool for analyzing the semantic features of an
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