Post on 20-Dec-2015
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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 sub-
directories 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 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 include physical disk addresses
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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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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 identification
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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 employee
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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.
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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 e-commerce 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 e-commerce 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