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Data Bases (Spanish

In: Computers and Technology

Submitted By drogo77
Words 1102
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Fundamentos Base de Datos

1. Aplicaciones de los sistemas de datos:

Las bases de datos son muy usadas y las mas significativas son:

• Banca • Líneas aéreas • Universidades • Producción • Recursos humanos • Telecomunicaciones • Tarjetas de crédito • Finanzas • Ventas

El uso de base de datos en estas áreas es esencial y hoy la mayoría de las empresas tienen base de datos.
Desde los inicios del internet, una de las cosas mas importantes es tener bases de datos porqué te reduce trabajo y hace mejor las cosas, como por ejemplo las librerías, las consultas de estados de cuenta en un banco, etc.

2. Sistemas de Base de Datos Frente a Sistemas de Archivos

Para poder cambiar y modificar la información, el sistema debe tener ciertas aplicaciones de un sistema operativo convencional que permite crear nuevos archivos o modificarlos, y para este proceso de almacenamiento se necesita mantener la información en un sistema de procesamiento.
Los inconvenientes son :

• Redundancia e inconsistencia de datos • Dificultad de acceso a los datos • Anomalías en el acceso recurrentes • Aislamiento de datos • Problemas de integridad (restricciones de consistencia) • Problemas de atomicidad (sujetas a fallo) • Problemas de seguridad

3. Visión de los Datos

Un sistema de bases de datos es una colección de archivos interrelacionados y un conjunto de programas que permitan a los usuarios acceder y modificar estos archivos. Uno de los propósitos principales de un sistema es dar una imagen de los datos.

los desarrolladores esconden la dificultad a los usuarios a través de varios niveles de abstracción para que entiendan mejor la interacción de los usuarios con el sistema:

• Nivel físico • Nivel lógico • Nivel de vistas

En el almacenamiento se deben insertar y borrar nuevas funciones por lo que crearon 2 tipos, uno cuando es solo un momento particular que se llama EJEMPLAR, y cuando es de toda la base se llama ESQUEMA.

4. Modelos de los Datos

• Modelo entidad-relación: se basa en la colección de datos básicos (entidades) y de relaciones con estos objetos. En una estructura lógica E-R consta de :

▪ Rectángulos: entidades ▪ Elipses: atributos ▪ Rombos: relación entre conjuntos y entidades ▪ Líneas: une atributos con conjuntos de entidades y éstos con las relaciones

• Modelo racional: Usa tablas para representar los datos y las relaciones entre ellos; es un modelo basado en registros, es decir que se estructura en un formato fijo de varios tipos.

• Otros modelos de datos: Modelo de datos orientado a objetos, Modelo de datos relacionado orientado a objetos, modelo de datos de red, modelo de datos jerárquico y modelo semi-estructurados.

5. Lenguajes de Bases de Datos

Un sistema de bases de datos proporciona un lenguaje de definición de datos para especificar el esquema de la base de datos y un lenguaje de manipulación de datos para expresar las consultas a la base de datos y las modificaciones.

El cambio en los datos es: • La recuperación de información almacenada en la base de datos. • La inserción de información nueva en la base de datos. • El borrado de información de la base de datos. • La modificación de información almacenada en la base de datos.

El acceso a base de datos desde programas de aplicación: son los que se usan para interaccionar con las bases de datos.

6. Usuarios y Administradores de la Base de Datos

Hay cuatro tipos diferentes de usuarios de un sistema de base de datos, diferenciados por la forma en que ellos esperan interactuar con el sistema. Se han diseñado diferentes tipo de interfaces de usuario para diferentes tipos de usuarios:

• Usuarios normales : Son usuarios no sofisticados que interactúan con el sistema mediante la invocación de alguno de los programas de aplicación permanentes que se ha escrito previamente. • Programadores de aplicaciones: profesionales informáticos. Utilizan Desarrollo Rápido de Aplicaciones que permiten construir formularios e informes sin escribir un programa • Usuarios sofisticados: interactúan con el sistema sin programas escritos, forman sus consultas por el programador de consultas transforman las instrucciones de LMD a el que el gestor de almacenamiento entienda. • Usuarios especializados: escriben aplicaciones fuera del procesamiento de datos tradicional; son sistemas mucho más complejos.

Funciones principales: • Definición del esquema: crear el esquema original • Definición de la estructura y del método de acceso • Modificaciones del esquema y de la organización física: permite reflejar las necesidades cambiantes de la organización.

7. Gestión de Transacciones

La atomicidad es que la transferencia de fondos debe ocurrir por completo o no ocurrir en absoluto.
La consistencia es que la ejecución de la transferencia de fondos preserve la consistencia de la base de datos.
La durabilidad es que los nuevos valores de las cuentas A y B deben persistir, a pesar de la posibilidad de fallo del sistema.
Una transacción es una colección de operaciones que se lleva a cabo como una única función lógica en una aplicación de bases de datos.

8. Estructura de un Sistema de base de Datos

Un gestor de almacenamiento es un modulo de programa que proporciona la interfaz entre los datos de bajo nivel en la base de datos y los programas de aplicación y consultas emitidas al sistema.
Estos componentes del gestor de almacenamiento tienen que tener varias cosas como:

• Gestor de autorización e integridad ▪ Archivos de datos ▪ Diccionario de datos ▪ Índices • Gestor de transacciones • Gestor de archivos • Gestor de memoria intermedia

Los componentes del procesador de consultas tienen:

• Interprete del LDD • Compilador del LMD • Motor de evaluación de consultas

9. Arquitecturas de Aplicaciones

Las aplicaciones de bases de datos se dividen usual- mente en dos o tres partes.

• En 2 partes : La aplicación se divide en un componente que esta en la maquina cliente, que llama al sistema de bases de datos en la maquina servidor por medio de instrucciones del lenguaje de consultas. • En 3 partes: la maquina cliente se comporta como frontal y no tiene ninguna llamada directa a la base de datos. En su lugar, el cliente se comunica con un servidor de aplicaciones, usualmente mediante una interfaz de formularios.

Las de 3 partes siempre son mejores para el internet WWW por sus aplicaciones.

10. Historia de los Sistemas de Base de Datos

• 1950 a 1960: Cintas magnéticas guardaban los datos, leer los datos de una cinta y escribirlos en una nueva cinta. • 1960 a 1970: Uso de discos fijos permitiendo el acceso directo a los datos. Se desarrollaros bases de datos de red y jerárquicas, haciéndose listas y árboles para almacenar en discos, • 1980: el mas importante objetivo era el procesamiento de transacciones. • 1990: Lenguaje SQL que ayuda a la toma de decisiones, intensivas en consultas, análisis de grandes cantidades de datos. • Finales de 1990: World Wide Web, soporte para transacciones más alta, fiabilidad y disponibilidad.

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