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Chapter 1. File Systems and Databases. Database Systems: Design, Implementation, and Management, 4th Edition Peter Rob & Carlos Coronel. Introducing the Database. Major Database Concepts Data and information Data - Raw facts Information - Processed data Data management Database - PowerPoint PPT Presentation
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11 File Systems and DatabasesChapter 1
Database Systems: Design, Implementation, and
Management, 4th Edition
Peter Rob & Carlos Coronel
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Introducing the DatabaseIntroducing the Database
Major Database Concepts Data and information
Data - Raw facts
Information - Processed data
Data management
Database
Metadata
Database management system (DBMS)
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Figure 1.1
Sales per Employee for Each of ROBCOR’S Two Divisions
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Introducing the DatabaseIntroducing the Database Importance of DBMS
It helps make data management more efficient and effective.
Its query language allows quick answers to ad hoc queries.
It provides end users better access to more and better-managed data.
It promotes an integrated view of organization’s operations -- “big picture.”
It reduces the probability of inconsistent data.
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Figure 1.2
The DBMS Manages the Interaction
Between the End User and the Database
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Introducing the DatabaseIntroducing the Database
Why Database Design Is Important?
A well-designed database facilitates data management and becomes a valuable information generator.
A poorly designed database is a breeding ground for uncontrolled data redundancies.
A poorly designed database generates errors that lead to bad decisions.
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Historical RootsHistorical Roots Why Study File Systems?
It provides historical perspective.
It teaches lessons to avoid pitfalls of data management.
Its simple characteristics facilitate understanding of the design complexity of a database.
It provides useful knowledge for converting a file system to a database system.
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Figure 1.3
Contents of the CUSTOMER File
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Table 1.1 Basic File TerminologyData “Raw” facts that have little meaning unless they have been
organized in some logical manner. The smallest piece of datathat can be “recognized” by the computer is a singlecharacter, such as the letter A, the number 5, or somesymbol such as; ‘ ? > * +. A single character requires onebyte of computer storage.
Field A character or group of characters (alphabetic or numeric)that has a specific meaning. A field might define a telephonenumbers, a birth date, a customer name, a year-to-date(YTD) sales value, and so on.
Record A logically connected set of one or more fields that describesa person, place, or thing. For example, the fields thatcomprise a record for a customer named J. D. Rudd mightconsist of J. D. Rudd’s name, address, phone number, dateof birth, credit limit, unpaid balance, and so on.
File A collection of related records. For example, a file mightcontain data about ROBCOR Company’s vendors; or, a filemight contain the records for the students currently enrolledat Gigantic University.
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Figure 1.4
Contents of the AGENT File
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A Simple File System
Figure 1.5
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File System CritiqueFile System Critique
File System Data Management
File systems require extensive programming in a third-generation language (3GL).
As the number of files expands, system administration becomes difficult.
Making changes in existing file structures is important and difficult.
Security features to safeguard data are difficult to program and usually omitted.
Difficulty to pool data creates islands of information.
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File System CritiqueFile System Critique Structural and Data Dependence
Structural DependenceA change in any file’s structure requires the modification of all programs using that file.
Data DependenceA change in any file’s data characteristics requires changes in all data access programs.
Significance of data dependence is the difference between the data logical format and the data physical format.
Data dependence makes file systems extremely cumbersome from a programming and data management point of view.
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File System CritiqueFile System Critique Field Definitions and Naming Conventions
A good (flexible) record definition anticipates reporting requirements by breaking up fields into their components.
Example:
– Customer Name Last Name, First Name, Initial
– Customer Address Street Address, City, State
FIELD CONTENTS
CUS_LNAME Customer last name
CUS_FNAME Customer first name
CUS_INITIAL Customer initial
CUS_AREACODE Customer area code
CUS_PHONE Customer phone
CUS_ADDRESS Customer street address or box number
CUS_CITY Customer city
CUS_STATE Customer state
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File System CritiqueFile System Critique
Field Definitions and Naming Conventions
Selecting proper field names is very important.
Names must be as descriptive as possible within restrictions.
Naming must reflect designer’s documentation needs and user’s reporting and processing requirements.
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File System CritiqueFile System Critique Data Redundancy:
Uncontrolled data redundancy sets the stage for
Data Inconsistency (lack of data integrity)
Data anomalies
Modification anomalies
Insertion anomalies
Deletion anomalies
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Figure 1.6
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Figure 1.7
The Database System Environment
Figure 1.7
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Database SystemsDatabase Systems
The Database System Components Hardware
Computer Peripherals
Software Operating systems software DBMS software Applications programs and utilities software
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Database SystemsDatabase Systems The Database System Components
People Systems administrators Database administrators (DBAs) Database designers Systems analysts and programmers End users
Procedures Instructions and rules that govern the design and use of
the database system
Data Collection of facts stored in the database
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Database SystemsDatabase Systems The Database System Components
The complexity of database systems depends on various organizational factors:
Organization’s size
Organization’s function
Organization’s corporate culture
Organizational activities and environment
Database solutions must be cost effective AND strategically effective.
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Database SystemsDatabase Systems Types of Database Systems
Number of Users Single-user
– Desktop database Multiuser
– Workgroup database– Enterprise database
Scope Desktop Workgroup Enterprise
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Database SystemsDatabase Systems
Types of Database Systems Location
Centralized Distributed
Use Transactional (Production) Decision support Data warehouse
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Database SystemsDatabase Systems DBMS Functions
1. Data Dictionary Management
2. Data Storage Management
3. Data Transformation and Presentation
4. Security Management
5. Multi-User Access Control
6. Backup and Recovery Management
7. Data Integrity Management
8. Database Access Languages (DDL and DML) and Application Programming Interfaces
9. Database Communication Interfaces
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Database ModelsDatabase Models A database model is a collection of logical
constructs used to represent the data structure and the data relationships found within the database.
Two Categories of Database Models Conceptual models focus on the logical nature of
the data representation. They are concerned with what is represented rather than how it is represented.
Implementation models place the emphasis on how the data are represented in the database or on how the data structures are implemented.
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Database Models Database Models Three Types of Relationships
One-to-many relationships (1:M) A painter paints many different paintings, but each one
of them is painted by only that painter.– PAINTER (1) paints PAINTING (M)
Many-to-many relationships (M:N) An employee might learn many job skills, and each job
skill might be learned by many employees.– EMPLOYEE (M) learns SKILL (N)
One-to-one relationships (1:1) Each store is managed by a single employee and each
store manager (employee) only manages a single store.– EMPLOYEE (1) manages STORE (1)
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Database ModelsDatabase Models
Three Types of Implementation Database Models
Hierarchical database model
Network database model
Relational database model
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A Hierarchical Structure
Figure 1.8
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Database Models Database Models Hierarchical Database Model
Basic Structure
Collection of records logically organized to conform to the upside-down tree (hierarchical) structure.
The top layer is perceived as the parent of the segment directly beneath it.
The segments below other segments are the children of the segment above them.
A tree structure is represented as a hierarchical path on the computer’s storage media.
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Database Models Database Models Hierarchical Database Model
Advantages Conceptual simplicity Database security Data independence Database integrity Efficiency dealing with a large database
Disadvantages Complex implementation Difficult to manage Lacks structural independence Applications programming and use complexity Implementation limitations Lack of standards
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Child with Multiple Parents
Figure 1.9
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Database Models Database Models Network Database Model
Basic Structure
Set -- A relationship is called a set. Each set is composed of at least two record types: an owner (parent) record and a member (child) record.
A set is represents a 1:M relationship between the owner and the member.
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A Network Database Model
Figure 1.10
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Database Models Database Models Network Database Model
Advantages Conceptual simplicity
Handles more relationship types
Data access flexibility
Promotes database integrity
Data independence
Conformance to standards
Disadvantages System complexity
Lack of structural independence
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Database Models Database Models Relational Database Model
Basic Structure RDBMS allows operations in a human logical
environment. The relational database is perceived as a collection of
tables. Each table consists of a series of row/column
intersections. Tables (or relations) are related to each other by
sharing a common entity characteristic. The relationship type is often shown in a relational
schema. A table yields complete data and structural
independence.
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Linking Relational Tables
Figure 1.11
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Database Models Database Models Relational Database Model
Advantages Structural independence Improved conceptual simplicity Easier database design, implementation, management,
and use Ad hoc query capability (SQL) Powerful database management system
Disadvantages Substantial hardware and system software overhead Possibility of poor design and implementation Potential “islands of information” problems
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A Relational Schema
Figure 1.12
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Database ModelsDatabase Models
Entity-Relationship Data Model It is one of the most widely accepted graphical data
modeling tools.
It graphically represents data as entities and their relationships in a database structure.
It complements the relational data model concepts.
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Database ModelsDatabase Models Entity Relationship Data Model
Basic Structure E-R models are normally represented in an entity
relationship diagram (ERD). An entity is represented by a rectangle. Each entity is described by a set of attributes. An
attribute describes a particular characteristics of the entity.
A relationship is represented by a diamond connected to the related entities.
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Figure 1.13 Relationship Depiction: The ERD
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Figure 1.14 Relationship Depiction: The Crow’s Foot
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Database ModelsDatabase Models Entity-Relationship Data Model
Advantages Exceptional conceptual simplicity
Visual representation
Effective communication tool
Integrated with the relational database model
Disadvantages Limited constraint representation
Limited relationship representation
No data manipulation language
Loss of information content
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Database ModelsDatabase Models Object-Oriented Database Model
Characteristics
An object is described by its factual content.
An object includes information about relationships between the facts within the object, as well as with other objects.
An object is a self-contained building block for autonomous structures.
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Database ModelsDatabase Models Object-Oriented Database Model
Basic Structure
Objects are abstractions of real-world entities or events.
Attributes describe the properties of an object.
Objects that share similar characteristics are grouped in classes.
A class is a collection of similar objects with shared structure (attributes) and behavior (methods).
Classes are organized in a class hierarchy.
An object can inherit the attributes and methods of the classes above it.
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A Comparison: The OO Data Model and the ER Model
Figure 1.15
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Database ModelsDatabase Models Object-Oriented Database Model
Advantages Add semantic content
Visual presentation includes semantic content
Database integrity
Both structural and data independence
Disadvantages Lack of OODM standards
Complex navigational data access
Steep learning curve
High system overhead slows transactions
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The Development of Data Models
Figure 1.16
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Wrap-Up: The Evolution of Data Models
Wrap-Up: The Evolution of Data Models
Common characteristics required for data models: A data model must show some degree of conceptual
simplicity without compromising the semantic completeness.
A data model must represent the real world as closely as possible.
The representation of the real-world transformations (behavior) must be in compliance with the consistency and integrity characteristics of any data model.
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Wrap-Up: The Evolution of Data Models
Wrap-Up: The Evolution of Data Models
Database Models and the InternetThe use of the Internet as a prime business tool is shifting focus to database products that interface efficiently and easily with the Internet.
Successful “Internet age” databases are characterized by:
Flexible, efficient, and secure Internet access. Support for complex data types and relationships. Seamless interfacing with multiple data sources and
structures. Simplicity of the conceptual database model. An abundance of available database tools. A powerful DBMS to help make the DBA’s job easier.
