Database Management Systems ISYS 464 Fall 2004 David Chao.

Database Management Systems ISYS 464

Fall 2004

David Chao

Introduction to Databases

• The most important component in an information system

• A group of related files– Created to support business operations:

• Day-to-day operations: TPS• Decision-makings: MIS, DSS• Strategic plans: ESS

– Integrated to reduce data duplication and maintain data consistency

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:

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

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)

Limitations of the File-Based Approach

• Duplication of data– Data inconsistency

• 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

Database Approach

• The database holds not only the data but also a description of the data.– System catalog (or data dictionary, or meta

data)• Data about data

– Program-data independence

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.

ANSI-SPARC Architecture• A three-level architecture to provide data

independence– External level: The user’s view of the database. This

level describes the part of the database that is relevant to each user.

– Conceptual level: This level describes what data is stored in the database and the relationships among the data.

– Internal level: The physical representation of the database on the computer. This level describes how the data is stored in the database.

• File organizations, indexes

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: • EmpID – 4 characters• EmpName – 30 characters• DateOfBirth – Date field 8 bytes• Salary – Number(7,2)• Sex – 1 character

– Physical level: • 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.

Advantages of DBMS

• Control of data redundancy

• Data consistency

• Support Ad Hoc queries

• Improved data integrity, security, backup and recovery, concurrency

Multi-User DBMS Architectures

• Teleprocessing: – One computer with a single CPU and a number of dumb terminals.– Add burden on the central computer, which not only had to run the

application programs and DBMS, but also had to carry out a significant amount of work on behalf of the terminals (such as formatting data for display)

• File-Server: – Applications run on workstations that contain a full copy of the

DBMS. File-server acts as a shared hard disk drive. The DBMS on each workstation sends requests to the file-server for data, but none of the processing is done by the server.

– Generate a significant amount of network traffic.

• Client-Server: – Computer network development– Balanced distributed processing

Client Database Server

SQL queries

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.

Advantages of Client-Server Architecture

• Enables wider access to databases.• Increased performance: Different CPUs can be

processing applications in parallel.• Hardware costs may be reduced: Only server

requires higher storage and processing power to manage the database.

• Network traffic is reduced: Only database requests and results are sent.

• Increased database integrity.

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 three components in a database application

1. Presentation – user interface• Menus, forms, reports, etc

2. Processing logic • Business rules

3. Database

Categories of Database Applications

• One-Tier– Legacy online transaction processing– PC database application

• Two-Tier client/server– Client-based presentation.– Processing logic is buried either inside the user interface

on the client or within the database on the server, or both.

• Three-Tier, N- tier– Processing logic is separated from the interface and

database.

Two-tier

• Simplicity• Provides a basic separation of tasks. The client is

primarily responsible for the presentation of data to user, and the server is primarily responsible for supplying data services to the client.

• Fat client: – More functions are placed on the client

• Fat server: – More functions are placed on the server.

Three-Tier

• 1. User interface, 2. Business logic and data processing layer, 3. Database server.

• Advantage:– Implementing business rules as components.

• Objects that provide services to other client applications.

– Application maintenance is centralized.

– Separation of the business logic from the database functions.

– Fit naturally to the Internet environment.

The Web as a Database Application Platform

• Three-tier architecture– Browser, web server, database server,

processing logic

• Advantages:– Cross-platform support– Graphical user interface

The Web as a Database Application Platform

• Disadvantages– Reliability: Internet is unreliable and slow.– Security– Costs: hardware and software 20%, marketing

24%, content development 56%.– Potentially enormous peak load.

Major Databse 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– Insertion only, no deletion

• Concurrent processing– Read/Write

• Transaction management

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 three-level database– Conceptual level:

• Data modeling, ERD, Normalization

– Physical level:• File organizations and index

– External level• Relational algebra, SQL, QBE

• Database management techniques