Uni 2 Fundamentos De Base De Datos

Fundamentos de Base
de Datos
Unidad 2. Diseño de Bases de Datos y el modelo E-R

2.1. El proceso de diseño
• Database systems are designed to manage large bodies of
information. These large bodies of information do not exist in
isolation. They are part of the operation of some enterprise whose
end product may be information from the database or may be some
device or service for which thedatabase plays only a supporting role.

2.1. El proceso de diseño
• Instead of representing all data in tables, it distinguishes between
basic objects, called entities, and relationships among these objects.
It is often used as a first step in database-schema design.

2.1. El proceso de diseño
• The task of creating a database application involving design of the
database schema design of the programsthat access and update the
data, and design of a security scheme to control access to data.

• ¿Cómo se diseña correctamente una base de datos?
• ¿Qué metodología de diseño de bases de datos conoces?
• ¿Crees que representar todos los datos de una empresa en tablas
aisladas sea eficiente, si/no y por qué?
• Nota: En el transcurso de esta unidad y al fin de ella debes ser capaz
de responder conclaridad las preguntas anteriores

Design Phases
• The database designer must interact with users of the application to
understand the needs of the application, represent them in a highlevel fashion that can be understood by the users, and then translate
the requirements into lower levels of the design.
1. The initial phase of database design is to characterize fully the data
needs of theprospective database users. The database designer
needs to interact extensively with domain experts and users to carry
out this task.

Design Phases
1. The outcome of this phase is a specification of user requirements.
2. The designer chooses a data model and, by applying the concepts of
the chosen data model, translates these requirements into a
conceptual schema of the database.
2. The schema developedat this conceptual-design phase provides a
detailed overview of the enterprise.

Design Phases
2. Typically, the conceptual-design phase results in the creation of an
entity-relationship diagram that provides a graphic representation
of the schema.

3. The designer reviews the schema to confirm that all data
requirements are indeed satisfied and are not in conflict with one
another. She can alsoexamine the design to remove any redundant
features.

Design Phases
3. A fully developed conceptual schema also indicates the functional
requirements of the enterprise.

4. In a specification of functional requirements, users describe the
kinds of operations (or transactions) that will be performed on the
data.

Design Phases
3. At this stage of conceptual design, the designer can review theschema to ensure it meets functional requirements.
4. The process of moving from an abstract data model to the
implementation of the database proceeds in two final design
phases. (next slide)

Design Phases
 In the logical-design phase, the designer maps the high-level conceptual
schema onto the implementation data model of the database system that
will be used. The implementation data model istypically the relational data
model, and this step typically consists of mapping the conceptual schema
defined using the entity-relationship model into a relation schema.
 Finally, the designer uses the resulting system-specific database schema in
the subsequent physical-design phase, in which the physical features of the
database are specified. These features include the form of file organizationand choice of index structures.

• Escribe con tus palabras en que consiste cada una de las fases de
diseño
• ¿Por qué crees que sea importante interactuar con el usuario final de
la base de datos y con expertos de la empresa que usarán la base de
datos (directa o indirectamente) en alguna fase del diseño?
• ¿Qué modelo de datos se adecua a las fases de diseño?

2.2 Modelo Entidad-Relación.
• El...