Database Management Systems
ISYS 464
David Chao
Introduction to Databases
• The most important component in an information
system
• Created to support all levels of business
operations:
– Day-to-day operations
• TPS, CRM, ERP
– Decision-makings
• DSS, data warehouse
– Strategic plans
Definitions
• Database: organized collection of logically related data
– A group of related files
• Data: stored representations of meaningful objects and
events
– Structured: Fixed format record
• numbers, text, dates
– Unstructured: images, video, documents
• Information: data processed to increase knowledge in the
person using the data
• Metadata: data that describes the properties and context of
user data
– data about data
Example of Metadata
Traditional File-Based Systems
• A collection of application programs that
perform services for the end-users. Each
program defines and manages its own data.
Example
Limitations of the File-Based
Approach
• Duplication of data
– Data inconsistency
– Limited data sharing
• Program-data dependence
– When file structure changed, all programs that access
the file must be modified to conform to the new file
structure.
– The definition of the data is embedded in the program.
• Fixed queries
– No facilities for asking unplanned, ad hoc queries
Problems with Program-Data
Dependency
• Each application program needs to include
code for the metadata of each file
• Each application program must have its
own processing routines for reading,
inserting, updating, and deleting data
Example: Comma-Delimited File
• It stores each data item with a comma separating
each item and places double quotes around string
fields.
• Student file with fields: SID, Sname, and GPA
– “S5”, ”Peter”, 3.0
– “S1”, “Paul”, 2.5
• Questions:
– How many students?
– What is average GPA?
Sequentially Accessing the Student File
to Compute Average GPA
Dim fileNumber, stCounter As Integer
Dim SID, SNAME As String
Dim gpa, sumGpa As Double
fileNumber = FreeFile()
FileOpen(fileNumber, "c:\stdata.txt", OpenMode.Input)
Do While Not EOF(fileNumber)
Input(fileNumber, SID)
Input(fileNumber, SNAME)
Input(fileNumber, gpa)
sumGpa += gpa
stCounter += 1
Loop
MessageBox.Show(sumGpa / stCounter.ToString)
Database Approach
• Central repository of shared data
• The database holds not only the data but also a
description of the data.
– System catalog (repository , data dictionary, or
metadata)
• A central location where data descriptions are stored.
• Data about data
– Program-data independence
• Demo: VS ProgramDataIndependenceDemo
Advantages of the Database
Approach
• Program-data independence
– The separation of data descriptions from the
application programs that use the data.
– Allows the data to change without changing the
application programs.
•
•
•
•
Planned data redundancy
Improved data consistency
Improved data sharing
Enforcement of standards
Database Management System
(DBMS)
• A software that enables users to define, create,
maintain, and control access to the database.
– Data Definition Language (DDL)
– Data Manipulation Language (DML)
– Control access:
• Security, integrity, concurrent access, recovery, support for
data communication, etc.
– Utility services
• File import/export, monitoring facilities, etc.
• Support Ad Hoc queries
Database Management System
• A software system that is used to create, maintain, and provide
controlled access to user databases
Order Filing
System
Invoicing
System
Payroll
System
DBMS
Central database
Contains employee,
order, inventory,
pricing, and
customer data
DBMS manages data resources like an operating system manages hardware resources
Evolution of DB Systems
Database Schema
• External Schema
– User Views
– Subsets of Conceptual Schema
• Conceptual Schema
– This level describes what data is stored in the database and the
relationships among the data.
– View of the data administrator
– E-R models
• Internal schema
– Logical schema
• Underlying implementation and design
– Relational table design
– Physical Schema
• File organizations, indexes
Figure 2-7 Three-schema architecture
Different people
have different
views of the
database…these
are the external
schema
The internal
schema is the
underlying
design and
implementation
Data Independence
• Data independence means that upper levels are
unaffected by changes to lower levels.
– Logical data independence
• Changes to the conceptual level, such as the addition of new
entities, attributes, or relationships, should be possible without
having to change the existing external level design.
– Physical data independence
• Changes to the physical level, such as using a different file
organization, indexes, should be possible without having to
change the conceptual level design.
Three-Level Example
Employee Entity
• Conceptual design:
– Employee entity with attributes: EmpID, EmpName, DateOfBirth,
Salary, and Sex.
• Internal level:
– Logical schema:
•
•
•
•
•
EmpID – 4 characters
EmpName – 30 characters
DateOfBirth – Date field 8 bytes
Salary – Number(7,2)
Sex – 1 character
– Physical schema:
• Record size = 4 + 30 + 8 + 7 +1 = 50 bytes
• Sequential file with index on EmpID field
• External level:
• EmpAgeView:
• EmpID, EmpName, Age=Year(Today()) – Year(DateOfBirth)
• EmpSalaryView: EmpID, EmpName, Salary
Benefits of Using Views
• Views provide a level of security.
• Views provide a mechanism to customize
the appearance of the database.
• Views provide a consistent, unchanging
picture of the database, even if the
underlying database is changed.
Database Application
• It is a program that interacts with the
database at some point in its execution by
issuing an appropriate request (typically an
SQL statement) to the DBMS.
• Database programming
The Range of Database Applications
• Personal databases:
– Desktop, PDA/Smart Phone
• Workgroup databases
• Departmental/divisional databases
• Enterprise database
– Enterprise Resource Planning (ERP)
• Integrate all enterprise functions (manufacturing, finance, sales,
marketing, inventory, accounting, human resources)
– Data Warehouse
• Integrated decision support system derived from various
operational databases
The three components in a
database application
1. Presentation – user interface
• Menus, forms, reports, etc
2. Processing logic
• Business rules
3. Database
SQL queries
Client
Database Server
Results
Database Server: A high processing power computer with
advanced DBMS.
Client: A PC that runs database applications.
SQL interface.
Client Functions
•
•
•
•
Manages the user interface.
Accepts and checks syntax of user input.
Implements business rules.
Generates database requests and transmits
to server.
• Passes response back to user.
Database Server Functions
• Checks authorization.
• Accepts and processes database requests from
clients.
• Ensures integrity constraints not violated.
• Performs query/update processing and transmits
response to client.
• Provides concurrent database access, transaction
management, and recovery control.
The Web as a Database Application Platform
• Three-tier architecture
– Browser, web server, database server,
processing logic
• Advantages:
– Cross-platform support
– Graphical user interface
Figure 2-9 Three-tiered client/server database architecture
Major Database Management Activities
• Creating database
• Updating database
• Querying database
Creating Database
• Analysis
– System analysis
• Data Flow Diagram, UML
– Data modeling
• ERD
• Design
– Maps the data model on to a target database model.
• Implementation: Efficiently store and retrieve data
– File organization and index
Updating Database
• Insertions, deletions, modifications
– Update pattern:
• Read only, Insertion only, no modification
• Concurrent processing
– Read/Write
• Transaction management
– Roll back
– Commit
Querying Database
• Relational algebra
• SQL
• QBE
New Developments in Database
•
•
•
•
•
Object-Oriented database
Object-Relational database
Decision support with data warehouse
Web based database applications
XML database
Course Overview
• An introduction to the design and use of database:
– Creating database:
• Analysis: Data modeling, ERD, Normalization
• Design: Relational database design
• Implementation:
– Use SQL data definition language to create database
– Updating database:
• SQL data manipulation language
– Querying database:
• SQL Select commands
• Other database management technologies:
–
–
–
–
File and index
Data warehouse
Database transaction management
Database security and management
Download DBMS
• MySQL 5.0 Community Server:
– http://dev.mysql.com/downloads/
• MS SQL Server 2005 Express:
– http://msdn.microsoft.com/vstudio/express/sql/download/
• Oracle 10g Express Edition:
– http://www.oracle.com/technology/products/database/xe/index.html
• Note: Remember the password!