CHAPTERS 1 and 2

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CHAPTERS 1 and 2

• Database Concepts and the 3-Schema Architecture

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Standard Definitions

• Dataraw facts that are unprocessed. No meaning
  to the organization
• Informationdata that is processed. Has
  organizational meaning
• KnowledgeInformation that is processed to give
  new information to the organization
• Data managementcreation, storage, retrieval, and
  processing of data
• DBMScollection of software that allows data
  management

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Key ConceptData Independence

• Database has separate identity from applications
• 3 Schema Architecture
• Layers the architecture of the database
• Supports structural independence
• Schemaa model of the database

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External Schema what user sees
Conceptual Schemahow db is logically designed
(ERD)
Internal Schemahow db is physically structured
and stored
3-Schema Architecture
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Conceptual SchemasLogical Representation (ERD)
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Conceptual Model (ERD)

• easily understood macro level view of data
  environment
• Independent of both software and hardware
• Changes in either the hardware or the DBMS
  software have no effect on the database design at
  the conceptual level

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Conceptual Model Basic Building Blocks

• Entity is anything about which data are to be
  collected and stored
• Attribute is a characteristic of an entity
• Relationship describes an association among (two
  or more) entities
• One-to-many (1M) relationship
• Many-to-many (MN or MM) relationship
• One-to-one (11) relationship

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Conceptual Schemas (ERD)
Always logical representation of
databi-directional associations
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Conceptual Relationships based on Business Rules

• Brief, precise, and unambiguous description of a
  policy, procedure, or principle within a specific
  organizations environment
• Description of operations that helps to create
  and enforce actions within that organizations
  environment
• Characteristics of datacompany perspective

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External Schemahow db looks to users
Conceptual Schemahow db is logically designed
Internal Schemahow db is physically structured
and stored
3-Schema Architecture
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The Internal ModelPhysical Model

• Representation of the database as seen by the
  data software
• Adapts the conceptual model to the DBMS
• Software dependent
• Hardware independent

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Internal SchemasPhysical Structure of the Data

• Hierarchical database model
• Network database model
• Relational database model
• Objected-oriented

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A Hierarchical Structure
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A Network Data Model
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Child with Multiple Parents
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The Relational Model

• Developed by Codd (IBM) in 1970
• Based on mathematical principlesVenn diagrams
• Considered ingenious but impractical in 1970 due
  to restrictions of mainframe environment
• Conceptually simpletables that are linked
  together by a common field

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The Relational Model

• Performs same basic functions provided by
  hierarchical and network DBMS systems, plus other
  functions
• Most important advantage of the relational model
  is its ability to let the user/designer operate
  in a human logical environment

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The Relational ModelBasic Structure

• Table (relation)
• Matrix consisting of a series of row/column
  intersections
• Tables are related to each other by sharing a
  common field
• Logical structure only

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Relational Model caused a revolution in database
design and development

• Stores a collection of related entities
• Resembles a flat file
• Relational table is purely logical structure
• How data are physically stored in the database is
  of no concern to the user or the designer

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A Relational Schema (Access example)
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Linking Relational Tables
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The Relational Model

• Advantages
• Structural independence
• Improved conceptual simplicity
• Easier database design, implementation,
  management, and use
• Ad hoc query capability
• Powerful database management system

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The External ModelUsers view

• End users view of the data environment
• Requires that the modeler subdivide set of
  requirements and constraints into functional
  modules
• Good design should
• Consider such relationships between views
• Provide programmers with a set of restrictions
  that govern common entities

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The External Model

• DBMS dependent
• Hardware independent

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Advantages of External Models

• Use of database subsets makes application program
  development much simpler
• Facilitates designers task by making it easier
  to identify specific data required to support
  each business units operations
• Provides feedback about the conceptual models
  adequacy
• Creation of external models helps to ensure
  security constraints in the database design

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Data Models A Summary

• Each new data model capitalized on the
  shortcomings of previous models
• Common characteristics
• Conceptual simplicity without compromising the
  semantic completeness of the database
• Represent the real world as closely as possible
• Representation of real-world transformations
  (behavior) must be in compliance with consistency
  and integrity characteristics of any data model

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The Development of Data Models