Database Design and Implementation CIS 591 Dr. Stephen C. Hayne
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Database Design and Implementation
CIS 591
Dr. Stephen C. Hayne
Outline
Historical development Terms and concepts Objectives of database systems
Timely and Accurate Information
United Airlines (290,000 flight coupons per day and electronic ticketing):– Assemble information dynamically– Get multiple perspectives on the data to
decide how to handle discrepancies– Increase accuracy on revenue figures– Improve scheduling, fares and
marketing
Databases Today
Big business in software industry ($>10B/year in US alone)
Field is still young (<30 years) Rapidly changing environment DBs are now pervasive
Payroll File
Soc.Sec.# Name Hours Rate
000-00-0000 Barbie 40 10.00
123-45-6798 Ken 40 20.00
987-65-4321 Barney 20 5.00
FieldsPrimary key
A “logical” record
COBOL Record Description
01 EMPLOYEE RECORD
03 SS# PICTURE X(11)
03 NAME PICTURE A(20)
03 HOURS PICTURE 9(2)
03 RATE PICTURE 99V99
Compiling a Program
COBOL Program
COBOL Compiler
Executable Program
Base Salary Added
Soc.Sec.# Name Hours Rate Salary
000-00-0000 Barbie 40 10.00 1000
123-45-6798 Ken 40 20.00 2000
987-65-4321 Barney 20 5.00 1
What does this imply for the program?
It means that...
We must modify » the file itself» the COBOL program
Re-compile the program Re-comple any program using that file Y2K anyone?
In the beginning (1960’s)
Sue Programmer
Payroll Program
Payrollfiles
Joe Programmer
Benefits Program
Benefitsfiles
Maintenance
Sue Programmer
Payroll Program
Payrollfile (mod)
Joe Programmer
Benefits Program
Benefitsfile
Mod
Mod
Expense Report
Expensefile
And it goes on....
Sue Programmer
Payroll Program
Payrollfile
Joe Programmer
Benefits Program
Benefitsfile
Mod
Mod
Expense Report
Expensefile
Thelma
Louise
Expensefile
Data File Summary
Data is separated and isolated. Data is often duplicated. Application programs are dependent on
file formats. Files are often incompatible. Data often not represented in user's
format.
Data Independence Decouple data from programs
PayrollProgram
BenefitsProgram
DBMS
IntegratedDatabase
Database Management Systems
DBMS: The software package» SQL Server, Oracle, Informix, DB2,
Sybase, Access, etc. Treat data as an organizational asset Manage data independently of programs Provide better access Provide information for management
Data as an Organizational Asset
Record keeping Accounting Managing / Decision Making
» Strategy» Quality» Customer service» Data mining» Business Process Reengineering
Strategic
Tactical
Operational
Organization LevelBroadLong-TermUnstructuredExternally-OrientedVolatileUnpredictable
NarrowShort-TermStructuredInternally-OrientedStablePredictableFinance Production Marketing
Database Applicability
Definition of a Database
A database is a model of a model A database is a self-describing
collection of integrated records» data» meta-data» indexes» application meta-data
Database Terms Entity (instance)
» an individual “thing” about which data is stored– a student, a car, a computer, an employee
» represented in a record Attribute
» a characteristic of an entity– student name, color of a car, make of computer
» represented in a field Entity type or class
» a set of entities of the same kind– the students at ASU, the set of pickup trucks
» represented in a relation or table (file)
Payroll Relation (Table)
Soc.Sec.# Name Hours Rate
000-00-0000 Barbie 40 10.00
123-45-6798 Ken 40 20.00
987-65-4321 Barney 20 5.00
AttributesPrimary key
Tuple (row)
Controlling Redundancy - effort duplication, wasted storage, inconsistencies
Standardization Data Sharing - concurrency control, user views Multiple Interfaces - query language, program interface,
menus, natural language Data Relationships Integrity Constraints - data types/relationships Backup and Recovery Productivity
DBMS Objectives
Three Schema Architecture
ExternalView
ExternalView
Conceptual Schema
Internal Schema
DBMS Architecture
Logical Independence
Physical Independence
Logical Independence - ability to changeconceptual schema without alteringexternal schemas
Physical Independence - ability to change internal schema with altering conceptual (or external) schemas
Increased overhead due to mapping
Data Independence
External Level
User views» What each user or user group “sees”» Only the entities, attributes and
relationships relevant to each user» May have aliases for attributes
– Customer vs. Patron
» May have different output formats– Negative values in red or in parentheses
Conceptual Level
The “logical schema”» ALL the entities, attributes and relationships» The constraints on the data» Semantic information about the data» Security and integrity information
The Internal Level
The physical schema Storage space allocation for data and
indexes Record descriptions Data compression and data encryption
techniques
Objectives of Database Systems
Access Flexibility» Query languages (DML)
– SQL (sometimes pronounced sequel)– QBE
» Embedded languages– SQL– CODASYL DML
» Forms and Reports
Objectives of Database Systems (Cont’d)
Data Integrity» Correct» Consistent» Current» Critical for users!
Objectives of Database Systems (Cont’d)
Data Security» Prevent unauthorized access» Prevent accidental damage» Recover if damage occurs
Objectives of Database Systems (Cont’d)
Reduced Data Redundancy» Store each datum in only one place » Disk space» Update problems
– Time– Data Integrity
Objectives of Database Systems (Cont’d)
Data Sharing» only among appropriate users» Compared to paper
– Paper in one place at a time– Databases shared by many at the same time– Can redesign systems
» Politically difficult– Who “owns” the data?– Who sees the data?– Who updates the data?
Objectives of Database Systems (Cont’d)
Relationships» among entities» For example, customers and orders.
– Each customer is related to zero, one or more orders.– Each order is related to one customer
Customer Order
Objectives of Database Systems (Cont’d)
Standardization» Data dictionary» Standard codes (M=Male, F=Female)» Standard formats (Gender is one letter)» Standard definitions
– What is a proposal?– What is a full-time student?
Objectives of Database Systems (Cont’d)
Personnel productivity» Share data definitions and databases» Share code» Don’t reinvent the wheel
Some Disadvantages
Complex, large, expensive software Hardware and conversion costs Performance problems Complex application development
» Large systems» Organizational considerations
Summary
Data is an important resource. Databases seek several objectives. Databases must be well-designed. Databases must be well-managed. The database environment is complex.
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