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Jerry PostCopyright © 1998
Database Management Database Management SystemsSystems
Chapter 1
Introduction
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Goal: Build a Business Application
Tools:Database DesignSQL (queries)Programming
Des
ign
SQ
L
Pro
gram
Des
ign
SQ
L
Pro
gram
Best:Spend your timeon design and SQL.
Worst:Compensate for poor designand limited SQL with programming.
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DBMS: Database Management System
DatabaseA collection of data stored in a standardized format,
designed to be shared by multiple users.
Database Management SystemSoftware that defines a database, stores the data, supports
a query language, produces reports, and creates data entry screens.
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Drawbacks of old File methods
Uncontrolled DuplicationWastes spaceHard to update all files
Inconsistent data Inflexibility
Hard to change dataHard to change programs
Limited data sharing Poor enforcement of standards Poor programmer productivity Excessive program maintenance
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File Method Problems
Files defined in programCannot read file without
definitionHard to find definitionEvery time you alter file,
you must rewrite codeChange in a program/file
will crash other codeCannot tell which
programs use each file
Multiuser problemsConcurrencySecurity
AccessBackup & Restore
Efficiency IndexesProgrammer talent
System Application
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Old File Method/3GL
Data Definition File 1 … File 2 …
Data Definition File A File 2 File C …
Pay History
Benefits
Employee
EmployeeChoices
FilesProgramsPayroll
Benefits
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Example of File Method v DBMS
File Division01 Employees 02 ID 02 Name 02 Address
01 Department 02 ID 02 . . .
COBOL
112 Davy Jones 999 ElmStreet . . . 113 Peter Smith101 Oak St . . .
Employee File
More programsFile Division01 Employees...
Add to file (e.g.Cell phone)Write code to copy employee file
and add empty cell phone slot.Find all programs that use
employee file.Modify file definitions.Modify reports (as needed)Recompile, fix new bugs.
Easier: Keep two employee files?
02 Cell Phone
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Advantages of Database Approach
Minimal data redundancy. Data consistency. Integration of data. Sharing of data. Enforcement of standards. Ease of application development. Uniform security, privacy and integrity. Data independence.
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Database Management Approach Data is most important
Data defined firstStandard format
Access through DBMSQueries, Reports, FormsApplication Programs3GL Interface
Data independenceChange data definition
without changing codeAlter code without
changing dataMove/split data without
changing code
All Data
DBMS
Program1 Program2QueriesReports
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Modifying Data with DBMS
Add cell number to employee tableOpen table definitionAdd data element If desired, modify reports
Use report writerNo programming
Existing reports, queries, code will all run as before with no changes.
Field Name Data Type Description
EmployeeID Number Autonumber..TaxpayerID Text Federal IDLastName TextFirstName Text . . . Phone Text . . .
CellPhone Text Cellular . . .
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DBMS Features/Components Database engine
StorageRetrievalUpdate
Query Processor Data dictionary Utilities Security
Report writer Forms generator (input
screens) Application generator Communications 3GL Interface
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DBMS Engine, Security, Utilities
DataTables
DatabaseEngine
ProductItemID Description887 Dog food946 Cat food
OrderOrderID ODate9874 3-3-979888 3-9-97
CustomerCustomerID Name1195 Jones2355 Rojas
ProductItemID Integer, UniqueDescription Text, 100 charCustomerCustomerID Integer, UniqueName Text, 50 char
SecurityUser IdentificationAccess Rights
Utilities
Concurrency andLock Manager
Backup andRecovery
Administration
DataDictionary
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DBMS Report WriterAll Data
Database EngineData Dictionary
Query Processor
Report Writer
ReportFormat
and Query
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DBMS Input FormsAll Data
Database EngineData Dictionary
Query Processor
Form Builder
InputForm
Design
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DBMS Components
All Data
Database EngineData Dictionary
Security
Query Processor
FormBuilder
ReportWriter
CommunicationNetwork
3GLConnector
Program
ApplicationGenerator
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Examples of Commercial Systems
Oracle Ingres Informix (Unix) DB2, SQL/DS (IBM) Access (Microsoft) SQL Server (Microsoft +) Many older (Focus, IMS, ...) Many limited PC (dBASE, Paradox, …)
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Hierarchical DatabaseCustomers
Orders
Item Description Quantity998 Dog Food 12764 Cat Food 11
Items
Customer
Order
Items Ordered
To retrieve data, you must start at the top (customer). When you retrieve a customer, you retrieve all nested data.
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Relational Database
Customer(CustomerID, Name, …
Order(OrderID, CustomerID, OrderDate, …
ItemsOrdered(OrderID, ItemID, Quantity, …
Items(ItemID, Description, Price, …
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Object-Oriented DBMSCustomer
CustomerIDName… Add CustomerDrop CustomerChange Address
OrderOrderIDCustomerID… NewOrderDeleteOrder…
OrderItemOrderIDItemID… OrderItemDropOrderItem…
ItemItemIDDescription… New ItemSell ItemBuy Item …
GovernmentCustomer
ContactNameContactPhoneDiscount, …
NewContact
CommercialCustomer
ContactNameContactPhone…
NewContact
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Why don’t all developers use a DBMS?
Most new projects (in last 5 years) do use a DBMS Need specialized personnel
ProgrammersDesigners/AnalystsDatabase administrators
Need to define data for organization Cost
PC: $400 - $2000Large: $100,000 +