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

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

DBMS manages data resources like an operating system manages hardware resources

• A software system that is used to create, maintain, and provide controlled access to user databases

Order Filing System

Invoicing System

Payroll System

DBMSCentral database

Contains employee,order, inventory,

pricing, and customer data

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

Different people have different views of the database…these are the external schema

The internal schema is the underlying design and implementation

Figure 2-7 Three-schema architecture

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 ExampleEmployee 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

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.

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:

• Insertion only, no modification

• 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

• Other database management technologies