Transcript ppt for session 5

LSU/SLIS
Databases
Session 5
LIS 7008
Information Technologies
Quiz
Avg
=88
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• Any homework
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• The Quiz
– Work on it on your own
• Discussions of any earlier session
– Contribute to your class participation credit!
Agenda
• Relational database design
– Relational DB, object-oriented DB, network
DB, hierarchical DB, etc.
• Microsoft Access
– DBMS for creating relational DB
– Graphical programming interface for skipping
SQL
– Oracle, Sybase, MySQL, Dbase, etc.
• Database (DB)
Databases
– A DB is a collection of data, organized to support access
– DB models some aspects of reality (such as university
enrollment), not everything in the world.
– DB has data itself, and the structure of data (for organizing
data).
• Data Base Management System (DBMS)
– Software to create and access databases
– DBMS is at the level of programming language. Computer
scientists design DBMS. MS-Access is a DBMS.
– LSU Computer Science Dept. offers CSC 4402 DBMS.
• Relational Algebra
– Special-purpose programming language to create DBMS
Structured Information in DB
• Database
• Table
A collection of tables
A collection of related records
– Each record is one row in the table
– Each field is one column in the table.
• Record A collection of related fields
– A row represents a record.
• Field
An “atomic” unit of data
– number, string, true/false, …
– A column represents a field; models some aspect of the
reality (e.g., attribute of an entity)
• Primary Key
record
The field that uniquely identifies a
– Values of a primary key must be unique
A Simple Example
primary key
Registrar Example: Enrollment
• Query: which students are in which courses?
– Relationship b/t students and courses is assigned
• What do we need to know about the students?
– What do you want to know about “students”?
– Attributes: first name, last name, email, department
– What about professors?
• What do we need to know about the courses?
– What do you want to know about “courses”?
– Attributes: course ID, description, enrolled students, grades
A “Flat File” Solution
Using MS-Excel
Student ID Last Name
1001 Arrows
1001 Arrows
1002 Peters
1002 Peters
1003 Smith
1004 Smith
First Name
John
John
Kathy
Kathy
Chris
John
Department IDDepartmentCourse ID Course description Grades
EE
EE
LIS7008 Information Technologies 90
EE
Elec Engin ee750
Communication
95
HIST
HIST
LIS 7008 Informatino Technology
95
HIST
history
hist405 American History
80
HIST
history
hist405 American History
90
SLIS
Info Sci
LIS7008 Information Technology
98
Discussion Topic
Why is this a bad approach?
email
jarrows@lsu
ja_2002@yahoo
kpeters2@lsu
kpeters2@lsu
smith2002@lsu
js03@lsu
Goals of “Normalization”
• Save space
– Save each fact only once
• More rapid updates
– Every fact only needs to be updated once
• More rapid search
– Finding something once is good enough
• Avoid inconsistency
– Changing data once changes it everywhere
Relational Algebra Terminology
• Tables represent “relations”
– “course ID” and “course description” are related.
– “Name” and “email address” are related.
• Named fields represent “attributes”
– Attributes of Course: course ID, description, …
– Attributes of Student: first name, last name, …
• Each row in the table is also called a “tuple”
– The order of the rows is not important
• Queries specify desired conditions
– The DBMS then finds data that satisfies them
A Normalized Relational Database
Student Table
Student ID
1001
1002
1003
1004
Last Name
Arrows
Peters
Smith
Smith
Department Table
Department ID
EE
HIST
SLIS
Department
Electronic Engineering
History
Library/Information Sci
First Name
John
Kathy
Chris
John
Department ID
EE
HIST
HIST
SLIS
email
jarrows@lsu
kpeters2@lsu
smith2002@lsu
js03@lsu
Course Table
Course ID
LIS7008
ee750
hist405
Course Description
Information Technologies
Communication
American History
Enrollment Table
Student ID
1001
1001
1002
1002
1003
1004
Course ID
LIS7008
ee750
LIS7008
hist405
hist405
LIS7008
Grades
90
95
95
80
90
98
A foreign key of a
table refers to the
primary key of an
other table. The
Enrollment Table has
two foreign keys.
Approaches to Normalization
• For simple problems (like the homework)
– Start with “binary relationships”
• Pairs of fields that are related, e.g., Student ID, Last Name
– Group together wherever possible
– Add keys where necessary
• For more complicated problems:
– Need to do Entity Relationship (E-R) modeling before
designing tables
– If interested, read Entity-Relationship Model at
http://en.wikipedia.org/wiki/Entity-relationship_model
Example of Join
Student Table
Student ID
Last Name
1001 Arrows
1002 Peters
1003 Smith
1004 Smith
Department Table
First Name
John
Kathy
Chris
John
Department ID
EE
HIST
HIST
SLIS
email
jarrows@lsu
kpeters2@lsu
smith2002@lsu
js03@lsu
Department ID
EE
HIST
CLIS
Department
Electronic Engineering
History
Library/Information Sci
“Joined” Table
Student ID
1001
1002
1003
1004
Last Name
Arrows
Peters
Smith
Smith
First Name
John
Kathy
Chris
John
Department IDDepartment
EE
Electronic Engineering
HIST
History
HIST
History
CLIS
Library/Information Sci
email
jarrows@lsu
kpeters2@lsu
smith2002@lsu
js03@lsu
Problems with Join
• Data modeling for “join” is complex
• “Join” is expensive to compute
– Both in time and storage space
• But it is “joins” that make databases relational
– Projection and restriction are also used in flat files
Some Lingo
• “Primary Key” uniquely identifies a record
– e.g. student ID in the Student table
• “Compound” primary key
– Synthesize a primary key with a combination of fields
– e.g., Student ID + Course ID in the Enrollment table
• “Foreign Key” in this table is a primary key in the
other table
– Note: it need not be unique in this table
• E.g., Department ID in the Student table is a foreign key; it is a
primary key in the Department table.
– Foreign keys are used to “join” other tables
Project
New Table
Student ID Last Name
1001 Arrows
1002 Peters
1003 Smith
1004 Smith
First Name
John
Kathy
Chris
John
Department IDDepartment
EE
Electronic Engineering
HIST
History
HIST
History
SLIS
Library/Information Sci
email
jarrows@lsu
kpeters2@lsu
smith2002@lsu
js03@lsu
SELECT Student ID, Department
Student ID
1001
1002
1003
1004
Department
Electronic Engineering
History
History
Library/Information Sci
Restrict
New Table
Student ID Last Name
1001 Arrows
1002 Peters
1003 Smith
1004 Smith
First Name
John
Kathy
Chris
John
Department IDDepartment
EE
Electronic Engineering
HIST
History
HIST
History
SLIS
Library/Information Sci
email
jarrows@lsu
kpeters2@lsu
smith2002@lsu
js03@lsu
SELECT * FROM New Table WHERE Department ID = “HIST”
Student ID Last Name
1002 Peters
1003 Smith
First Name Department IDDepartment
Kathy
HIST
History
Chris
HIST
History
email
kpeters2@lsu
smith2002@lsu
Entity-Relationship (E-R)
Diagrams
• Graphical visualization of the data model
– a visual representation of an entity-relationship
model.
• Entities are captured in boxes
• Relationships are captured using arrows
Registrar E-R Diagram
Enrollment
Student
Course
Grade
…
has
associated with
has
Course
Course ID
Course Name
…
Student
Student ID
First name
Last name
Department
E-mail
…
offered by
Department
Department ID
Department Name
…
Types of Relationships
Many-to-Many
M:N
1-to-Many
1:M
1-to-1
1:1
A More Complex E-R Diagram
cadastral: a public record, survey, or map of the value, extent, and
ownership of land as a basis of taxation.
Source: US Dept. Interior Bureau of Land Management,
Federal Geographic Data Committee Cadastral Subcommittee
http://www.fairview-industries.com/standardmodule/cad-erd.htm
Databases in the Real World
• Some typical database applications:
–
–
–
–
Banking (e.g., saving/checking accounts)
Trading (e.g., stocks)
Airline reservations
What if you screwed up your org’s DB?
• Characteristics:
–
–
–
–
Lots of data
Lots of concurrent access
Must have fast access
“Mission critical”
Database Integrity
• Registrar database must be internally consistent
– Enrolled students must have an entry in student table
– Courses must have a name
• What happens:
– When a student withdraws from the university?
• What tables are affected?
– When a course is taken off the books?
Integrity Constraints
• Conditions that must always be true
– Specified when the database is designed
– Checked when the database is modified
• R-DBMS ensures integrity constraints are respected
– So database contents remain faithful to real world
– Helps avoid data entry errors
Referential Integrity
• Foreign key values must exist in other table
– If not, those records cannot be joined
• Can be enforced when data is added
– Associate a primary key with each foreign key
• Helps avoid erroneous data
– Only need to ensure data quality for primary keys
Concurrency
• Thought experiment: You and your project
partner are editing the same file…
– Scenario 1: you both save it at the same time
– Scenario 2: you save first, but before it’s done
saving, your partner saves
Whose changes survive?
A) Yours B) Partner’s C) neither D) both E) ???
Concurrency Example
• Possible actions on a checking account
– Deposit check (read balance, write new balance)
– Cash check (read balance, write new balance)
• Scenario:
– Current balance: $500
– You try to deposit a $50 check and someone tries to
cash a $100 check at the same time
– Possible sequences: (what happens in each case?)
Deposit: read balance
Deposit: write balance
Cash: read balance
Cash: write balance
Deposit: read balance
Cash: read balance
Cash: write balance
Deposit: write balance
Deposit: read balance
Cash: read balance
Deposit: write balance
Cash: write balance
Database Transactions
• Transaction: sequence of grouped database actions
– e.g., transfer $500 from checking to savings
• “ACID” properties
– Atomicity
• All-or-nothing: either all related transactions made or nothing made
– Consistency
• Each transaction must take the DB between consistent states.
– Isolation:
• Concurrent transactions must appear to run in isolation
– Durability
• Results of transactions must survive even if systems crash
– Transactions are logged
Making Transactions
• Idea: keep a log (history) of all actions carried
out while executing transactions
– Before a change is made to the database, the
corresponding log entry is forced to a safe location
the log
• Recovering from a crash:
– Effects of partially executed transactions are undone
– Effects of committed transactions are redone
RideFinder Database Exercise
• Suppose you run a small business on campus
– say, Student Ride Booking Company
• Design a database to match passengers with available
rides over the Spring Break
– Drivers phone in available seats
• They want to know about interested passengers
– Passengers call up looking for rides
• They want to know about available rides
– These things happen in no particular order
– Your business is to assign rides to passengers
• This exercise may take 20-30 minutes.
Exercise Goals
• Identify the tables you will need
– First decide what data you will save
• What questions will be asked by passengers/drivers?
– These will be the queries
– Then decide how to group/split it into tables
• Start with binary relations if that helps
• Design the queries
– Using join, project and restrict
• Add primary and foreign keys where needed
Exercise Logistics
• Best work in groups of 3 or 4 students
– Although you can work by yourself
• Brainstorm data requirements for 5 minutes
– Do passengers care about the price of a ride?
– Do drivers care how much luggage there is?
• Develop tables and queries for 15 minutes
– Don’t get hung up on one thing too long
• Compare your answers with another group
– Should take about 5 minutes
RideFinder Database
• See my Sample Database (RideFinder): on
Syllabus page (under Notes)
How to Read a Database File
Using MS-Access
• To view the structure of a table: right-click
a table, view "design view".
• To view the data of a table: first view
"design view", then click View Datasheet
view.
• To view a query: right-click the query, view
"design view".
• To run a query: double click the query.
Database “Programming”
• Natural language queries
– Goal is ease of use
• e.g., Show me the last names of students in SLIS
• vocal queries
– Ambiguity sometimes results in errors
• Structured Query Language (SQL)
– Consistent, unambiguous interface to any DBMS
– Simple command structure:
• e.g., SELECT LastName FROM Students WHERE Dept=SLIS
– Useful standard for inter-process communications
• Visual programming (e.g., Microsoft Access)
– Unambiguous, and easier to learn than SQL
SQL: The SELECT Command
• Project chooses columns
– Based on their label
• Restrict chooses rows
– Based on their contents
• e.g. department ID = “HIST”
• These can be specified together
– SELECT Student ID, Dept FROM New Table WHERE
Department ID = “HIST”
SQL: Restrict Operators
• Each SELECT contains a single WHERE
• Numeric comparison
<, >, =, <>, …
• e.g., grade<80; price<20
• Boolean operations
– e.g., Name = “John” AND DeptID <> “HIST”
– <> means not equal to
Using Microsoft Access
Procedure
• Create a DB
– Click Blank Database
– Define file name (e.g., mydb.accdb)
– Click Create
• Create Tables
–
–
–
–
–
Click Create  Table
In the Ribbon, get Design View of the table
Define table name, save
Name your fields, specify field properties
Define Primary Key (a field of a table)
MS-Access
Create Records and Relationships
• Create Records
– Get a table’s Datasheet View
– Input data for each record
– Click Save icon when done
• Create/add Relationships
– Click Database Tool tab
– Click Relationships
– To create/add a relationship between two tables:
• put cursor on one field of a table, click and drag it onto a
field of another table
MS-Access
Create Queries
•
•
•
•
•
Click Create  Query Design
Select the tables involved
Define fields and criteria
Define query name, save
Double click the query to run
MS-Access 2010 Tutorials
• My tutorial:
– http://www.csc.lsu.edu/~wuyj/Teaching/7008/sp14/
SampleDB/Access2010/Access2010.html
• Other people’s tutorials:
– See syllabus page (under Useful Resources)
MS-Access 2007 Tutorials
• My tutorial:
– http://www.csc.lsu.edu/~wuyj/Teaching/7008/sp1
4/SampleDB/Access2007/Access2007.html
• Other people’s tutorials:
– See the syllabus page (under Useful Resources)
– http://holowczak.com/microsoft-access-2007-and-2010-tutorial/
– http://inpics.net/tutorials/access2007/basics.html
– http://www.officetutorials.com/Access%202007%20tut.DOC
MS-Access 2000-2003 Tutorials
• My tutorial:
http://www.csc.lsu.edu/~wuyj/Teaching/7008/sp1
4/SampleDB/Access2000/Access2000.html
• Other tutorials:
– http://www.cwnresearch.com/resources/databases/acces
s/tutorials/access2000/Access2000Tutorial.html
– https://www.courses.psu.edu/infsy/infsy540_gjy1/acces
s_tutorial_2000.html
Using Microsoft Access 2000-2003
• Create a database called rides.mdb
– FileNewBlank Database
• Specify the fields (columns)
– “Create a Table in Design View”
• Fill in the records (rows)
– Double-click on the icon for the table
MS-Access 2000-2003
Creating Fields
• Enter field name
– Must be unique, but only within the same table
• Select field type from a menu
– Use date/time for times
– Use text for phone numbers
• Designate primary key (right mouse button)
• Save the table
– That’s when you get to assign a table name
MS-Access 2000-2003
Entering Data
• Open the table
– Double-click on the icon
• Enter new data in the bottom row
– A new (blank) bottom row will appear
• Close the table
– No need to “save” – data is stored automatically
MS-Access 2000-2003
Building Queries
• Copy ride.mdb to your computer
• “Create Query in Design View”
– In “Queries”
• Choose two tables
• Pick each field you need using the menus
– Unclick “show” to not project
– Enter a criterion to “restrict”
• Save, exit, and reselect to run the query
Fun Facts about Queries
• “Joins” are automatic if field names are same
– Otherwise, drag a line between the fields
• Sort order is easy to specify
– Use the menu
• Queries form the basis for reports
– Reports give good control over layout
– Use the report wizard - the formats are complex
Other Things to Know
• Data input forms manage input better than
raw tables
– Invalid data can be identified when input
– Graphics can be incorporated
Key Ideas
• Relational Databases are a good choice when you
have:
– Lots of data
– And a problem that contains inherent relationships
• Design before you implement
– This is just another type of programming
– The mythical person-month applies!
• Join is the most important concept
– Project and restrict just remove undesired stuff
Discussion Point:
Mythical Person-Month
• Why is software development different
from manufacturing car?
• If it would take 1 person 3 months, why
does it take 4 people 6 months?
• Reminder: read the Mythical Person-Month
paper posted on the syllabus page
Trading People and Months is Hard
• Sequential constraints
– in the procedure of software development
• Communication
– between team members
• Training
– if new members join the team
Estimating Completion Time
• Rules of thumb
–
–
–
–
1/3 specification
1/6 coding
1/2 test planning, testing, and fixing!
This applies to your course project!
• Add time for coding to learn as you go, but don’t
take time away from the other parts!
– Reread the section on “gutless estimating” if you are
tempted
HW5: “type mismatch in query"
• Problem1:
Every time I run a query it says "Type
mismatch in query."
• Problem 2: My database cannot enforce referential
integrity.
• Solution: In order to remain data integrity, databases
declares the types of data. For instance, if the StudentID in
Table1 is a "string" type, and the StudentID in Table2 is a
"number" type, when you want to relate the two fields, the
DBMS reports a "type mismatch" error. So to correct such
a mistake, you need to go back to the structures of the both
tables, and check the types of the two fields to make sure
their types match.
Project
• Find a client
• Student Trip Travel Insurance
– https://sites01.lsu.edu/wp/riskmgt/student-triptravel-insurance
– Please fill out the online form before going to
meet with your client
• Project management issues
– Read paper on Man-mythical theory
• Copyright and information ethics issue