Transcript Wrap-up, review

IT420: Database Management and
Organization
Wrap-up
28 April 2006
Adina Crăiniceanu
www.cs.usna.edu/~adina
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Final Exam
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Monday, 1330, Michelson 223
Comprehensive
Closed books / closed notes
One double-sided page with notes
 NO duplicates
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Topics Not Covered
 SQL Cursors
 ODBC
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SQL Cursor
 Problem:
 SQL SELECT returns multiple rows
 Application programs (PHP,C, C#,…) need to
process the rows, one at a time
 Solution:
 Establish a cursor, a pointer to first row in the
result set
 Assign values in that row to variables
 Move the pointer to next row
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Process Rows Example - PHP
<?php //query
$query = "select title from songs where title like
'%Home%'";
//process results
$results = mysql_query($query)
or die("could not retrieve rows");
while ($row = mysql_fetch_array($results)){
echo 'Title: '.$row[title].' <br>';
}
?>
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SQL Cursor Example – SQL Server
//declare cursor
DECLARE MyCursor CURSOR FOR
SELECT title FROM songs WHERE title like '%Home%
//process rows
OPEN MyCursor
FETCH NEXT FROM MyCursor INTO @title
WHILE @@FETCH_STATUS = 0
BEGIN
print @title
FETCH NEXT FROM MyCursor INTO @title
END
//close and free cursor
CLOSE MyCursor
DEALLOCATE MyCursor
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Standards for Accessing DBMS
 OBDC (Open Database Connectivity) is
the early standard for relational databases.
 OLE DB is Microsoft’s object-oriented
interface for relational and other
databases.
 ADO (Active Data Objects) is Microsoft’s
standard providing easier access to OLE
DB data for the non-object-oriented
programmer.
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The Web Server Data Environment
 A Web
server
needs to
publish
applications
that involve
different
data types.
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The Role of the ODBC Standard
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ODBC Architecture
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Example Code…Familiar??
<?php
$connect = odbc_connect("mydbs", “root", "");
$query = "SELECT name, surname FROM users";
$result = odbc_exec($connect, $query);
while(odbc_fetch_row($result)){
$name = odbc_result($result, 1);
$surname = odbc_result($result, 2);
print("$name $surname\n");
}
// close the connection
odbc_close($connect); ?>
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Final Exam Main Topics
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ER Model
Relational Model
ER to Relational
Normalization
SQL
SQL Views
SQL Triggers
SQL Stored Procedures
PHP/MySQL
Database Administration
Storage and Indexing
XML
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ER Model and Relational Model
 ER:
 Entities
 identifiers
 Relationships
 cardinality
 Relational model
 Tables
 Constraints
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ER to Relational
 Transform entities in tables
 Transform relationships using foreign keys
 Specify logic for enforcing minimum
cardinalities
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Class Exercise: Transform ER
model into Relational Model
CLUB
FAALicense
AIRCRAFT
FAA number
Address
Phone
Min Cardinality:1
ModelNumber
Color
OWNER
Name
Phone
Min Cardinality:1 Address
MEMBER
Name
Phone
Rating
TotalHours
FLIGHT
FlightID
RentalDate
ReturnDate
TimeFlown
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Relational Model
CLUB
FAALicense: CHAR(18) NOT NULL
AIRCRAFT
FAA number: CHAR(18) NOT NULL
Address: CHAR(18)
Phone: CHAR(18)
ModelNumber: CHAR(18) NOT NULL (FK)
FAALicense: CHAR(18) (FK)
Color: Text(20)
OWNER
Name: CHAR(18) NOT NULL
Phone: CHAR(18) NOT NULL
Address: CHAR(18) NOT NULL
OWNERSHIP
FAA number: CHAR(18) NOT NULL (FK)
Name: CHAR(18) NOT NULL (FK)
Phone: CHAR(18) NOT NULL (FK)
MEMBER
Name: CHAR(18) NOT NULL
Phone: CHAR(18) NOT NULL
Rating: Long Integer
TotalHours: Long Integer
FAALicense: CHAR(18) (FK)
FLIGHT
FlightID: CHAR(18) NOT NULL
RentalDate: CHAR(18)
ReturnDate: CHAR(18)
Name: CHAR(18) NOT NULL (FK)
Phone: CHAR(18) NOT NULL (FK)
TimeFlown: CHAR(18)
FAA number: CHAR(18) NOT NULL (FK)
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Relationship lines
Useful?
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Table blueprints
CLUB
OWNER
FAALicense: CHAR(18) NOT NULL
Name: CHAR(18) NOT NULL
Phone: CHAR(18) NOT NULL
Address: CHAR(18)
Phone: CHAR(18)
Address: CHAR(18) NOT NULL
MEMBER
OWNERSHIP
Name: CHAR(18) NOT NULL
Phone: CHAR(18) NOT NULL
FAA number: CHAR(18) NOT NULL (FK)
Name: CHAR(18) NOT NULL (FK)
Phone: CHAR(18) NOT NULL (FK)
Rating: Long Integer
TotalHours: Long Integer
FAALicense: CHAR(18) (FK)
AIRCRAFT
FLIGHT
FAA number: CHAR(18) NOT NULL
FlightID: CHAR(18) NOT NULL
ModelNumber: CHAR(18) NOT NULL (FK)
FAALicense: CHAR(18) (FK)
Color: Text(20)
RentalDate: CHAR(18)
ReturnDate: CHAR(18)
Name: CHAR(18) NOT NULL (FK)
Phone: CHAR(18) NOT NULL (FK)
TimeFlown: CHAR(18)
FAA number: CHAR(18) NOT NULL (FK)
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Normalization
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Data Redundancy
Number LastName FirstName
Email
Rating
Wage
190
Smith
John
[email protected]
4
25
673
Doe
Jane
[email protected]
7
35
312
Doe
Bob
[email protected]
8
40
152
Johnson
Matt
[email protected]
7
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Application constraint:
All employees with same rating have the same wage (Rating Wage)
Problems due to data redundancy?
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Modification Anomalies
 Deletion Anomaly: What if we delete all
employees with rating 8?
 Lose wage info
 Insertion Anomaly: What if we need wage for
rating 12 with no employee having that rating?
 Cannot insert wage without employee
 Update Anomaly: What if we change the wage
for rating 7 to be 37?
 Could change for only some rows, not all
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Update Anomalies
 The EMPLOYEE table before and after an incorrect
update operation on Wage for Rating = 7
Number LastName FirstName
Email
Rating
Wage
190
Smith
John
[email protected]
4
25
673
Doe
Jane
[email protected]
7
35
312
Doe
Bob
[email protected]
8
40
152
Johnson
Matt
[email protected]
7
35
FirstName
Email
Rating
Wage
Number LastName
190
Smith
John
[email protected]
4
25
673
Doe
Jane
[email protected]
7
37
312
Doe
Bob
[email protected]
8
40
152
Johnson
Matt
[email protected]
7
35
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Table decomposition
Number LastName
FirstName
Email
Rating
Wage
190
Smith
John
[email protected]
4
25
673
Doe
Jane
[email protected]
7
35
312
Doe
Bob
[email protected]
8
40
152
Johnson
Matt
[email protected]
7
35
Number LastName FirstName
Email
Rating
Rating
Wage
4
25
190
Smith
John
[email protected]
4
673
Doe
Jane
[email protected]
7
7
35
312
Doe
Bob
[email protected]
8
8
40
152
Johnson
Matt
[email protected]
7
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Functional Dependency (FD)
 A functional dependency: the value of
one (a set of) attribute(s) determines the
value of a second (set of) attribute(s):
Alpha  MIDNName
Alpha  (MIDNName, MIDNClass)
(NbHours, HourlyPrice)Charge
 The attribute(s) on the left side of the
functional dependency is called the
determinant
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Functional Dependencies in the
SKU_DATA Table
Assuming data is representative, determine the FD
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Functional Dependencies in the
SKU_DATA Table
SKU  (SKU_Description, Department, Buyer)
SKU_Description  (SKU, Department, Buyer)
Buyer  Department
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Key
 A set of columns is a key for a relation if :
1. a) No two distinct rows can have same values in all
key columns
or equivalently
b) determines all of the other columns in a relation
2. This is not true for any subset of the key
 Part 2 false? A superkey
 Candidate key = key
 Primary key
 Alternate key
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Normal Forms
 1NF – A table that qualifies as a relation is in 1NF
 2NF – A relation is in 2NF if all of its nonkey attributes
are dependent on all of the primary key
 3NF – A relation is in 3NF if it is in 2NF and every
determinant is a superkey
 Boyce-Codd Normal Form (BCNF) – A relation is in
BCNF if every determinant is a (candidate) key
“I swear to construct my tables so that all nonkey
columns are dependent on the key, the whole key
and nothing but the key, so help me Codd.”
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Eliminating Modification Anomalies from
Functional Dependencies in Relations
 Put all relations into Boyce-Codd Normal Form
(BCNF):
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Putting a Relation into BCNF:
SKU_DATA
SKU_DATA
(SKU, SKU_Description, Department, Buyer)
SKU  (SKU_Description, Department, Buyer)
SKU_Description  (SKU, Department, Buyer)
Buyer  Department
SKU_DATA
(SKU, SKU_Description, Buyer)
BUYER
(Buyer, Department)
Where BUYER.Buyer must exist in SKU_DATA.Buyer
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Putting a Relation into BCNF:
New Relations
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Database Administration
 Concurrency Control
 Security
 Recovery
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Concurrency Control
 Concurrency control: ensure that one
user’s work does not inappropriately
influence another user’s work
 No single concurrency control technique is
ideal for all circumstances
 Trade-offs need to be made between level of
protection and throughput
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Atomic Transactions
 A transaction, or logical unit of work (LUW), is
a series of actions taken against the database
that occurs as an atomic unit
 Either all actions in a transaction occur - COMMIT
 Or none of them do - ABORT
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Concurrent Transaction
 Concurrent transactions: transactions
that appear to users as they are being
processed at the same time
 In reality, CPU can execute only one
instruction at a time
 Transactions are interleaved
 Concurrency problems
 Lost updates
 Inconsistent reads
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Lost Update Problem
 T1: R(item)
W(item)
 T2:
R(item)
Commit
W(item) Commit
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Inconsistent-Read Problem
 Dirty reads – read uncommitted data
 T1: R(A), W(A),
R(B), W(B), Abort
 T2:
R(A), W(A), Commit
 Unrepeatable reads
 T1: R(A),
R(A), W(A), Commit
 T2:
R(A), W(A), Commit
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Serializable Transactions
 Serializable transactions:
 Run concurrently
 Results like when they run separately
 Strict two-phase locking – locking technique to
achieve serializability
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Deadlock
 Deadlock: two transactions are each waiting on a
resource that the other transaction holds
 Preventing deadlock
 Allow users to issue all lock requests at one time
 Require all application programs to lock resources in the same
order
 Breaking deadlock
 Almost every DBMS has algorithms for detecting deadlock
 When deadlock occurs, DBMS aborts one of the transactions
and rollbacks partially completed work
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Optimistic versus Pessimistic
Locking
 Optimistic locking assumes that no transaction
conflict will occur:
 DBMS processes a transaction; checks whether
conflict occurred:
 If not, the transaction is finished
 If yes, the transaction is repeated until there is no conflict
 Pessimistic locking assumes that conflict will
occur:
 Locks are issued before a transaction is processed,
and then the locks are released
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Declaring Lock Characteristics
 Most application programs do not explicitly declare locks
due to its complication
 Mark transaction boundaries and declare locking
behavior they want the DBMS to use
 Transaction boundary markers: BEGIN, COMMIT, and
ROLLBACK TRANSACTION
 Advantage
 If the locking behavior needs to be changed, only the lock
declaration need be changed, not the application program
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ACID Transactions
 Transaction properties:
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Atomic - all or nothing
Consistent
Isolated
Durable – changes made by commited transactions
are permanent
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Consistency
 Consistency means either statement level or
transaction level consistency
 Statement level consistency: each statement
independently processes rows consistently
 Transaction level consistency: all rows impacted by
either of the SQL statements are protected from
changes during the entire transaction
 With transaction level consistency, a transaction may not see
its own changes
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Isolation : Inconsistent-Read
Problem
 Dirty reads – read uncommitted data
 T1: R(A), W(A),
 T2:
R(A), W(A), Commit
R(B), W(B), Abort
 Unrepeatable reads
 T1: R(A),
R(A), W(A), Commit
 T2:
R(A), W(A), Commit
 Phantom reads
 Re-read data and find new rows
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Transaction Isolation Level
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Indexing
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Hash Index
Constant search time
Equality queries only
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B+ Tree Index
~logdN search time
d – fan-out (~150)
N – number of data entries
Supports range queries
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Use of Indexes To Retrieve Data
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Class Exercise
What index would you construct?
1. SELECT *
FROM Mids
WHERE Company=02
2. SELECT CourseID, Count(*)
FROM StudentsEnroll
WHERE Company = 02
GROUP BY CourseID
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SOFs
 www.sof.cs.usna.edu
 Choose as password a random number
between 1 and 100
 If cannot login, try another number
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