Transcript Technology Focus: Database Systems IS605/606: Information Systems Instructor: Dr. Boris Jukic

IS605/606: Information Systems
Instructor: Dr. Boris Jukic
Technology Focus:
Database Systems
File systems
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File systems rely on coded file management programs to
access, insert and modify their content
As such, file systems are plagued by two main problems
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Structural dependence refers to the fact that if a file structure is
changed (such as deletion or addition of a field), the related file
management programs have to be modified accordingly
Data dependence refers to the fact that the changes in data
characteristics, such as changing a field from integer to decimal
(or even just changing the length of the field), will cause the
related file management programs to be changed
Finally, there is a problem of data redundancy
Data Redundancy
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When the same data is stored in more than
one location (in multiple files or multiple fields
within one file) It may lead to:
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Data integrity (inconsistency) problems
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may be caused by either data entry errors or failure to
update all multiple copies of the same data
Data anomalies: modification, insertion and
deletion
Data Redundancy in File Systems and
Resulting Anomalies
Product ID
001
001
001
002
002
003
003
Product Name Product Description
Product Price Customer ID Customer Name Customer Location Quantity Sold
PlainSounder AM/FM Radio, 2 speakers
$51
C1
Chrysler Corp
Germany
15000
PlainSounder AM/FM Radio, 2 speakers
$51
C2
Circuit City
California
18400
PlainSounder AM/FM Radio, 2 speakers
$51
H1
Hyundai
Korea
26500
BetterBox
Radio, CD, 6 Speakers
$123
G1
GM
Michigan
23650
BetterBox
Radio, CD, 6 Speakers
$123
F1
Ford Motors
Michigan
14000
UltraX
CD, MP3, 8 Speakers
$270
H2
Honda
Japan
7500
UltraX
CD, MP3, 8 Speakers
$270
B1
BMW
Germany
2560
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Modification anomaly: if PlainSounder model description
changes
Insertion Anomaly: if a new customer (Toyota for example) is
added to the list of those who buy BetterBox product
Database Systems
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Database Systems achieve data independence and
structural independence
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If data type of as filed is changed or a field is eliminated or a
new one added, the existing management programs
(queries) do NOT have to be modified
If properly designed, databases have a low level of
redundancy, eliminating most of the insertion,
deletion and modification anomalies
Logically related data instead of physically
separated and unrelated files
Relational Database Management
System
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In RMDBS, all data appears to be stored in a
collection of tables (or relations), which are
independent of one another, but can be
linked through common entries in one of the
tables' columns or fields (controlled
redundancy)
Relational Schema: The graph depicting
relationship types between tables
Relational Schema
Reduced Data Redundancy
Products
Customers
Product Id
Product Name
Product Description
Product Price
001
PlainSounder
AM/FM Radio, 2 speakers
002
BetterBox
Radio, CD, 6 Speakers
$123.00
003
UltraX
CD, MP3, 8 Speakers
$270.00
Customer ID
Customer Name
Customer Location
Product ID
C1
Chrysler
Germany
001
C2
Circuit City
California
001
H1
Hyundai
Korea
001
G1
GM
Michigan
002
F1
Ford Motors
Michigan
002
H2
Honda
Japan
003
B1
BMW
Germany
003
$51.00
Tables in RDBMS
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Tables: Logical constructs containing individual entity sets.
Tables are always two-dimensional: rows and columns
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each row represents a single entity (or entity instance) from the
entity set
each (uniquely named) column represents one attribute
each row-column intersection results in a single data value
Each table must have a primary key : An attribute uniquely
identifying each row (entity), satisfying the entity integrity
conditions. Null value (no entry) is not permitted for a primary
key.
The order of rows and columns within the table is irrelevant
Foreign Key is an attribute in one table whose values must
either match the value of a primary key in another table or be
set to null (no value). These conditions are known as referential
integrity constraint.
Relationships within the relational
database:
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One-to-one relationships:
One-to many relationships:
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Examples:
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professor - class
department - employee
Many to-many relationships
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Examples: parts – product, student – class, …
it is recommended to break it into a set (usually
two) of one-to-may relationships through a so
called composite (bridge) entity
Enterprise data planning
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A large component of the business
informational needs can be captured by the
mapping of all entities the organizations need
to keep track of and the relationships among
them
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E-R (Entity-Relationship) modeling is a standard
technique that provides a simplified picture of the
relationship among entities.
Entities and Attributes
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Entities and Attributes
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An entity (or entity instance) is a person, place,
event, or thing for which we intend to collect data.
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University -- Students, Faculty Members, Courses
Airlines -- Pilots, Aircraft, Routes, Suppliers
Each entity has certain characteristics known as
attributes.
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Student -- Student Number, Name, GPA, Date of Enrollment,
Date of Birth, Home Address, Phone Number, Major
Aircraft -- Aircraft Number, Date of Last Maintenance, Total
Hours Flown, Hours Flown since Last Maintenance
E-R Diagrams
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E-R Diagram (ERD) elements:
– Rectangles are used to represent entities.
– Diamonds are used to represent the relationship(s) between
the entities.
– The number 1 is used to represent the “1” side of the
relationship.
– The letter M is used to represent the “many” sides of the
relationship.
1 to Many Relationship
1 to Many Relationship: another example
Many to Many Relationship
E-R Diagram: An example