Transcript Lab Session-II CS121 Summer

Applications of Computers
 We talk about databases and their
implementation
 Implementation of databases involves trees
therefore we introduce trees
 E-commerce (BTC) allows web-based
access of inventory and orders
 Where are the inventory and orders stored?
In the corporate database
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Web-Based Forms+Server Side Scripts
Allow E-Commerce Interaction
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Databases
 Databases are implemented in many forms on all
possible platforms
 Think of flight reservation, credit card accounts,
registration for a semester, payrolls, IRS records,
SS records,……
 We interact almost daily with at least one database
in our day to day activities
A
database contains records that contain
information
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Database Concepts
 A database is usually a large collection of
information
 A DBMS (Database Management System)
is implemented to retrieve information from
a database in an effective and efficient way
 Database itself is implemented in files that
contain records. Each record contains data
fields having item-specific information
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Database Concepts: An example
Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999
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Use of Indices in Searching
 If you store information in the way shown, you
may want to select a specific person’s record
 In order to select the appropriate record, you have
to spell out the last name of a person
 The last name serves as a search
index as all the
records matching this last name can be retrieved
(http://www.switchboard.com)
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Use of Indices in Searching
 The database files searched this way are
called Indexed files
 Indexed files can be implemented with
Binary Search Tree (BST)
 The BST nodes contain the data values of
the indexed fields e.g. last names
 Additionally, a link is provided to the actual
file
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Trees
 A Binary Search Tree is a data structure
that is very useful in search applications
 A natural tree has a root from which
everything starts
 It has branches and leaves
 Think about your family tree
 Look at an organization chart for a company
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Trees
 Think about the way directories are
organized in your computer
 There is a root directory C:\
 Then there are sub-directories
 Sub-directories can also have further subdirectories
 This is the directory tree
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Binary Tree
 A binary tree is a tree in which each node
can have just two children
 Binary tree is easy to sketch
 Start with a root node (root is at the top as
opposed to natural trees)
 One child is shown on left and the other one
is shown on right
 The children can also have maximum two
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children each
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Binary Search Tree
 A binary search tree is a specialized type of
tree
 In BST, a node can have only two children
(right and left)
 The value of the left child is LESS than the
value of the parent node
 The value of the right child is MORE than
the value of the parent node
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A Plain Binary Tree
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A Binary Search Tree
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Class Exercise
 Make a BST from the list shown. Assume that
the numbers are to be entered into the BST
from left to right. The first number will be
taken as the root.
 [4,2,1,3,6,5,7]
 Assume that we are searching for two specific
numbers in this tree. The numbers are 6 and 9
 How many comparisons are needed to finish
the search?
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Use of Indices in Searching
 Let us consider the implementation of
indices into database files
 Indexing can be implemented with our
friendly BST
 The BST nodes contain the data values of
the indexed fields e.g. last names
 Additionally, a link is provided to the actual
file
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BST and Actual File
Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999
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Network Database Model
 The need for a convenient query language and
interaction developed for applications beyond
payrolls and inventory databases
 The programmers worked to link records in
separate files together
 This model is called “network database model”
because it uses a network of links between files
 Programmers must be aware of physical
organization of files and links
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Network Database Model
Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999
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Relational Database Model
 Relational database model was introduced
in late 70’s
 This model gives a more conceptual view of
the database
 It establishes a logical relationship between
records using one field as a logical link
 The information needed to employ
relational database is intuitive and does not
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include physical disk addresses
Relational Database Model
Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999
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Relational Database Model
Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999
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Comparing Both Models
 Network model is much faster than the
relational model because the links are
physical disk addresses
 Relational model is more flexible so it can
handle different types of queries
 RDBMS performs search after search to
retrieve information from different files
 The tradeoff is flexibility vs speed
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Airline Reservation System
 When we reserve a seat in a flight, the agent
interacts with the database
 The types of queries are limited to a few
options (class, fare, availability, restrictions)
 There are thousands of queries in progress
at any given time
 We want the database to be fast and
efficient
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Player Performance Statistics
 During televised games, comments are
made on certain players
 For example, Mark has a batting average of
0.407 against the Braves, etc.
 This information is obtained on the fly from
a database of player performance
 We want this database to be flexible as
many different types of queries are allowed
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Example of a Central Database
 AFIS is FBI’s Automated Fingerprint
Identification System
 It provides a national database of digitized
fingerprints
 California requires thumb prints on driver
licenses
 International travelers may be provided with
smart cards and checked with hand
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identification
Creating Your Own Database
 Large databases cannot be implemented on
personal computers
 For PC’s, the relational database model is
more appropriate as the number of data
items is small and speed is not a primary
concern
 MS-Access is used to implement databases
on PC platform
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Defining the Database Structure
 Initial work involves deciding about the
contents of individual fields and overall
organization
 Each field can contain only one type of data
 Related data files are called tables
 A table is an object that stores data in
records (rows) and fields (columns). The
data is, for example, about a customer or an
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employee
A Table in MS-Access
 In table Design view, you can create an
entire table from scratch, or add, delete, or
customize an existing table's fields.
 In table Datasheet view, you can add, edit,
or view the data in a table. You can also
check the spelling and print your table's
data, filter or sort records, change the
datasheet's appearance, or change the table's
structure by adding or deleting columns. 30
Databases in MS-Access
 In order to facilitate entry of data, MS-
Access provides forms. Forms can be
designed through the Forms tab
 Queries and Reports can be created to
interact with the database and extract data
that meets certain search requirements or it
has been sorted. Reports generate nice
formatted display of the output data
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Forming Queries
 Queries are requests for specific
information that meet a certain criteria
 Queries are written in a query language
 Normally, queries act as the only user
interface in a database
 Store cashier, bank teller clerk, payroll data
entry operators….all use query language to
interact with the databases
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Forming Queries
 SQL (“sequel”) stands for structured query
language and it is a de-facto standard
 SQL queries are simple and you do not need
to know programming to form these queries
 For example, to show all items whose value
exceeds $200 in the inventory database:
 SELECT Item-Name FROM Inventory
WHERE Value>$200
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Natural Language Queries
 Work is in progress to have a natural
language query system
 For example, the above question could be
re-phrased as “Find the item names from
inventory whose value exceeds $200”
 One of the search engines on the web,
AltaVista, supports natural language queries
 QBE(Query-by-example) is also popular and MS-
Access uses it by having criteria field in query
design
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The Web Interface
 Web and database technologies are merging
providing exciting opportunities
 (Think about the e-commerce, it has
become possible for you to book a flight,
browse through items and buy things
online)
 “Web database front-ends” provide forms using
which users can make selections as per their
criteria and interact with the database
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Web Interface
 Web interface supports http (hyper text
transfer protocol) that runs over TCP/IP
 This protocol supports transfer of text,
graphics and applets, thus opening a lot of
possibilities
 Industry is interested in small gadgets
running http protocol that can exchange
information in a secure way
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E-Commerce
 Almost all major companies have their
homes on the web, mainly for advertising
 Companies were reluctant towards ecommerce but now it is picking up
 The most revolutionary e-commerce is
between business and customer
 Business-business e-commerce is already
developed
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E-Commerce Requirements
 E-commerce between customer and
business requires several functions
 For example, auction sites should have the
capability to track bids by various people
 Also, multi-vendor selling sites should
support tracking of multiple companies
 Transactions between customers and the ecommerce site should be safe and secure
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The Credit Card Concerns
 Almost all e-commerce sites offer credit
card support
 A customer who wants to buy something
pays with credit card
 The credit card information is transmitted
through the public network and it can be
tapped by someone in the middle
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Encryption and Data Security
 For successful e-commerce, we must ensure
that the sensitive data has been encrypted
and secured
 Encryption transforms the data using a
“key” into a value that is meaningless in its
normal form
 This encrypted value can only be decrypted
by authorized agency or person
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Securing the Connection
 For protecting the credit card info, it is
transmitted under SSL (secure sockets
layer)
 It means the card info is encrypted and it is
very difficult to break the code by an
intruder
 Surprisingly, the misuse of the card info by
employees is a more serious concern
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