Applications of Computers Lectures 1 and 2

1. Applications of Computers Lectures 1 and 2 • Let us revise “indexing into the arrays” • Later, we will look at databases and their applications • Databases have wide-spread applications in all walks of life • We will introduce network model and relational model of database

2. Indexing into arrays • Let us assume an array declared as: • int ages_of_kids[4]; • ages_of_kids[0] = 7; • ages_of_kids[1] = 6; • ages_of_kids[2] = 4; • ages_of_kids[3] = 2;

3. Array Contents Values stored in the array 7 6 4 2 0 1 2 3 Index into the locations of the array

4. Array Indexing • Tell me at location 0, what is the index and what is the value?? • In C++, • int index; • index=0; • cout<<age_of_kids[index]; • What is the result? • Write a loop to print all values in the array

5. 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,……the list is endless • Everyday, we interact with at least one database in our day to day activities • Database contains records that contain information

6. 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

7. Database Concepts: An example Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999

8. Use of Indices in file management • 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 • This last name serves as a search index as all records matching this last name can be retrieved (http://www.switchboard.com)

9. Use of Indices in File Management • The database files searched this way are called “Indexed files” • Indexed files are implemented usually 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

10. Trees • A binary tree is a data structure that is very useful in search applications • Trees are everywhere • A natural tree has a root from which everything starts • Think about your family tree • Look at an organization chart for a company

11. 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

12. 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

14. 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 ROOT • The value of RIGHT child is MORE than the value of ROOT

15. A Plain Binary Tree

16. A Binary Search Tree

17. How to Have a Balanced BST • The selection of value for root node is very important • For example, look at the list of numbers presented here and make a BST from it • [1,2,3,4,5,6,7] What is the depth? • Now look at the list of numbers presented here and make a BST from it • [4,2,1,3,6,5,7] What is the depth?

18. Use of Indices in File Management • Indexed files are implemented usually with our friendly 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 • A BST should be balanced in order to cut down the search overhead

19. BST and Actual File Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999

20. 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

21. Network Database Model Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999

22. 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

23. Relational Database Model Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999

24. Relational Database Model Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999

25. 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

26. 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

27. 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

28. 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

29. 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 will be used as an example to illustrate the database management on PC’s

30. 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

31. 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.

32. Databases in MS-Access • In MS-Access, you can create a new database with simple graphical interface • As soon as you name your database, you are presented with a window having six tabs • We define four basic tabs here • Data will be kept in tables. You have to create a new table and define its fields (columns). You should use the design view to create the table

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. Alternate Payment Methods • DIGICASH is an alternate payment method that does not use credit cards for online buying • Customer opens an account and an electronic wallet is created at customer’s machine • Customer is able to create digital coins that are certified by the bank

45. Digicash is now eCash • http://www.ecashtechnologies.com/ • The new p2p technology is developed by the eCash technologies • Refer to the link below: • http://www.ecashtechnologies.com/Press/Press/Release030800.asp

46. Alternate Payment Methods • The bank attaches a digital signature to each digital coin • Thus, the customer can send digital cash to the vendor and buy anonymously • VIRTUAL PIN allows credit card charges without transmitting card number • The bank holds customer’s credit card information and issue a virtual PIN to customer

47. Alternate Payment Methods • Customer specifies virtual PIN to a merchant when charging something to credit card • Merchant sends this PIN to bank for verification • Bank requests customer authorization via email and on confirmation, charges the amount of sale to customer’s credit card