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INFORMATION TECHNOLOGY IN BUSINESS AND SOCIETYSESSION 15 – RELATIONAL DATABASES
SEAN J. TAYLOR
ADMINISTRATIVIA
• Assignment 3: Due tonight at midnight(AdSense in a week)
• Midterm back on Thursday
• Database tutorial led by Varun
• Assignment 4: Posted Thursday, due Friday 3/30
ADMINISTRATIVIA II
• Groups:I will email a form for you to list up to five classmates and then choose the groups. You can list 0-5.
• 2-way feedback:1. I will send you an anonymous survey.2. I will send you a brief summary of your current grade.
LEARNING OBJECTIVES
1. Understand what relational databases are (or, why text files and Excel are not enough)
2. Identify and distinguish between the following parts of a relational database: tables, records, fields, field values
3. Understand three types of anomalies that arise from un-normalized data
4. Understand how primary keys and foreign keys are used to link tables.
WHY ARE DATA VALUABLE?
RELATIONAL DATABASES
• Store data (insert)• Retrieve data (query)
• Software applications• Operations
• Analyze data (reporting capabilities)
WHY NOT STORE DATA LIKE THIS?
Order# Date Customer ID Last Name First Name Address ISBN Book Name Author Price
1 9/1/03 C1001 Bezos Jeff 1 Amazon Plaza #0465039138 Code and other laws of cyberspace Lessig, Lawrence $25.00
2 9/2/03 C1004 Sproull LeeDean's Office, Stern School, New York #1573928895
Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
3 9/3/03 C1002 Student Pat Tisch LC-12, New York #0072952849 MIS in the Information Age Haag, Stephen $98.75
4 9/4/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206679
Linked: The New Science of Networks
Barabasi, Albert-Laszlo $34.95
5 9/5/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206083
Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
6 9/6/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
7 9/7/03 C1002 Student Pat Tisch LC-12, New York #1573928895Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
8 9/8/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
RELATIONAL DATABASES
• Databases that use a series of logically related two-dimensional tables to store their information
• Tables are comprised of fields/records, which in turn contain field values
Last Name SS# DOB Major
Smith 100201122 06/11/84 IS
Kim 200202222 1/1/85 FIN
Davis 300201232 12/31/81 MKT
Pat 999132212 3/3/88 ACC
StudentTable
Field
Record
Field value
Relational DatabaseTables
Records FieldsField valuesBytes, bits
Last Name SS# DOB Major
Smith 100201122 06/11/84 IS
Kim 200202222 1/1/85 FIN
Davis 300201232 12/31/81 MKT
Pat 999132212 3/3/88 ACC
StudentTable
Field
Record
Field value
RELATIONAL DATABASES
ADVANTAGES1. Consistency
• We can restrict the values of certain fields (e.g. dates, integers)
• We can impose other kinds of constraints (all costs must be positive, last names must be included, orders must have addresses)
• Data look the same to all users at the same time.2. Centralization
• Many different users can edit and view the data simultaneously. Efficient sharing of information.
3. Efficient Querying
• SQL and other query languages can be used to create complex reports quickly
PROBLEMS WITH EXCEL?
When should you use a database instead of Excel?
– Insertion anomalies
– Deletion anomalies
– Update anomalies}Data Quality Problems
Should we just create multiple workbooks in Excel?
– The real power of a database: Querying
– How would you answer the following question in Excel?
– Find customers that spend on average $50 per book order, that live on West Coast or on the East Coast (but not in Midwest) and whose annual income is at least $150K
INSERTION ANOMALIES
• Inability to insert a piece of information about an object without having to insert a (bogus) piece of information about something else
• Example: Adding a new customer/book before it is orderedHow can you add the book “Harry Potter” in the file below?
Order# Date Customer ID Last Name First Name Address ISBN Book Name Author Price
1 9/1/03 C1001 Bezos Jeff 1 Amazon Plaza #0465039138 Code and other laws of cyberspace Lessig, Lawrence $25.00
2 9/2/03 C1004 Sproull LeeDean's Office, Stern School, New York #1573928895
Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
3 9/3/03 C1002 Student Pat Tisch LC-12, New York #0072952849 MIS in the Information Age Haag, Stephen $98.75
4 9/4/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206679
Linked: The New Science of Networks
Barabasi, Albert-Laszlo $34.95
5 9/5/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206083
Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
6 9/6/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
7 9/7/03 C1002 Student Pat Tisch LC-12, New York #1573928895Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
8 9/8/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
DELETION ANOMALIES• The loss of a piece of information about one object when a
piece of information about a different object is deleted
• Example: Deleting order 2 => deleting customer Lee Sproull
• Example: Deleting order 1 => deleting book “Code…”Order# Date Customer ID Last Name First Name Address ISBN Book Name Author Price
1 9/1/03 C1001 Bezos Jeff 1 Amazon Plaza #0465039138 Code and other laws of cyberspace Lessig, Lawrence $25.00
2 9/2/03 C1004 Sproull LeeDean's Office, Stern School, New York #1573928895
Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
3 9/3/03 C1002 Student Pat Tisch LC-12, New York #0072952849 MIS in the Information Age Haag, Stephen $98.75
4 9/4/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206679
Linked: The New Science of Networks
Barabasi, Albert-Laszlo $34.95
5 9/5/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206083
Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
6 9/6/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
7 9/7/03 C1002 Student Pat Tisch LC-12, New York #1573928895Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
8 9/8/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
UPDATE ANOMALIES• A need to change the same piece of information about an
object multiple times
• Example: Changing Jeff Bezos address in order 1 leaves orders 6 and 8 unchanged…
Order# Date Customer ID Last Name First Name Address ISBN Book Name Author Price
1 9/1/03 C1001 Bezos Jeff 1 Amazon Plaza #0465039138 Code and other laws of cyberspace Lessig, Lawrence $25.00
2 9/2/03 C1004 Sproull LeeDean's Office, Stern School, New York #1573928895
Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
3 9/3/03 C1002 Student Pat Tisch LC-12, New York #0072952849 MIS in the Information Age Haag, Stephen $98.75
4 9/4/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206679
Linked: The New Science of Networks
Barabasi, Albert-Laszlo $34.95
5 9/5/03 C1003 Gates BillMicrosoft Corporation, Redmond #0738206083
Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
6 9/6/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
7 9/7/03 C1002 Student Pat Tisch LC-12, New York #1573928895Digital Copyright: Protecting Intellectual Property on the Internet Litman, Jessica $55.00
8 9/8/03 C1001 Bezos Jeff 1 Amazon Plaza #0738206083 Smart Mobs: The Next Social Revolution Rheingold, Howard $29.95
ENTITY-RELATIONSHIP DIAGRAMS
MODELING DATA WITH
ENTITY RELATIONSHIP DIAGRAM
• The aim of an ERD is to model the data within the Information System.
• Provides a CONCEPTUAL DATA MODEL:a concept of the system, independent of implementation
1. What data should be stored?
2. What relationships exist between items of data?
ENTITIES
An entity can be uniquely identified.
Organizations collect and store data about entities:
• if a bank stores data about you - you are an entity• if a business stores a piece of paper called an invoice - the
invoice is an entity• a library stores data about a particular book - the book is
an entity
An actual, real thing or person about which data might be stored is referred to as an entity.
An actual, real thing or person about which data might be stored is referred to as an entity.
RELATIONSHIPS
• Entities are associated with each other via relationships.
• A relationship is a named association between two or more entity types:
Player TeamPlays for
DEFINING RELATIONSHIPS
Entity-relationship (E-R) diagram: a graphic method of representing entity classes and their relationships.
• Rectangle – entity class
• Dotted line – relationship
• | – single relationship
• O – zero or optional relationship
• Crow’s foot () – multiple relationship
The types of relationships reflect the business rules applicable to the entities
SIMPLE HOSPITAL EXAMPLE
In a hospital system, each ward has many patients who are cared for by nurses assigned to the specific ward. Patients may require treatment by more than one specialist doctor. A patient belongs to only one ward.
SIMPLE HOSPITAL EXAMPLE
In a hospital system, each ward has many patients who are cared for by nurses assigned to the specific ward. Patients may require treatment by more than one specialist doctor. A patient belongs to only one ward.
SIMPLE HOSPITAL SYSTEM
• Ward has many patients (1:N)• Patients are cared for by nurses (N:M)• Ward has assigned many nurses (1:N)• Patients require treatment by one or
more doctor (N:M)
SIMPLE HOSPITAL SYSTEM ERD
WARD
NURSE PATIENT
DOCTOR
treatsaccommodateshas
assigned
caresfor
UNIVERSITY DATABASE EXAMPLE
A department has many Professors. A Professor belongs to only one department. The department offers many different courses, and many Professors can teach a single course. A Professor can also teach more than one course. Students enroll for many courses and courses have many students. A course belongs to only one department.
NORMALIZATION
FITTING DATA INTO THE RELATIONAL MODEL
NORMALIZING AMAZON’S DATA• The process of assuring that a database can be implemented
effectively as a set of two-dimensional tables
• Unlike Excel though, the tables are connected
• Prevents insertion, deletion and update anomalies
CONNECTING TABLES TOGETHER
Primary keys– A field (or group of fields in some cases) that uniquely
describes each record in a table
– Examples: Customer ID, ISBN, Order#
Foreign keys– A field that is a primary key in one table and appears in a
different table (though not as the primary key)
– Examples: Customer ID in Orders
Integrity constraints– Rules that help ensure data quality
Each record should have a unique primary key
DATABASE SCHEMASummary of the logical structure of your database
– The tables in your database, along with each of their fields, keys
– The relationships between the tables
Primary key Primary key
Primary key
Foreign key
Foreign key
NEXT CLASS:SQL
• Do the SQL tutorial athttp://sqlzoo.net/(at least sections 0-3)
• Download the “Facebook” database from Blackboard and make sure you can open it in MS Access
• Interest in OSS databases?
• Bring a laptop if you want.
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