Week of 29th Lecture 1

1
Week of 29th Lecture 1

• Sample JavaScript Assignment
• Search Engines (Chapter 5)
• Programming Languages (Chapter 10)
• Exchange Sort Algorithm Example

2
Information Search

• The obvious directory for numbers, registrar
  for grade related queries
• Online libraries e-journals, e-books etc

3
Information Organization

• Categorize/Classify
• Arrange into different levels
• Hierarchy
• Media Print/Broadcast/Digital
• Digital media eg Slashdot/Digg/NYT
• NYT articles Edit/Sports/Inal/Business/NY
  Region/US

4
Hierarchy/tree concepts

• Branch
• Leaf
• Overlap
• Partition

5
Search Engine

• Collection of computer programs that help find
  information on the WEB (WWW)
• Two parts
• -- Crawler/Spider
• -- Query Processor

6
Crawler works

• Scans webpage
• Indexes keywords (those in title/body)
• Identifies links to other pages
• These linked pages to do list
• Visits next page in to do list
• Google allows web authors to submit web pages to
  its list

7
(No Transcript)
8
Query Processor works

• User enters search string
• Searches index to find URL associated with those
  query words.
• Why Google special ? Indexes based on anchor text
  as keyword - even if page not crawled but is
  linked to a page crawled it shows up in search
  result

9

• Still some pages never crawled, some pages have
  only images or unrecognizable format etc.
• Millions of results still, how do you order them?

10
Another Google SpecialPage Rank

• Decides order for search result
• Based on number of hits
• No. of hits No. of websites that link to that
  page
• Rank of page that links to page in question also
  affects rank

11
To get better results..

• Logical operators
• - AND ? Both
• - OR ? Either
• - NOT
• - ? search for the exact string between
  quotes

12
Check Legitimacy of website

• Check registration/owner data
• who is database
• InterNIC.net

13
Algorithm

• Systematic way produce a specific result
• Mathematical operations add, sub etc.
• Steps to starting an eden account, driving
  instructions, recipe etc

14
Essential Properties

• Input specified eg. Search query
• Output specified eg. Search result
• Definiteness which operations
• Effectiveness mechanically doable
• Finiteness stop eventually

15
Language

• Natural Language imprecise, ambiguous
• Eg. Double meaning for same words
• Lie/lie , fell/fell etc.
• Same meaning two words
• Programming Language Formal language designed
  to express algorithm.
• (both programmer computer agree upon same
  meaning)

16
While designing algos

• Capability (of doer)
• Language
• Context assumptions about the input and
  settings
• Eg. Last name, driving instructions (give start
  point, end point, direction, distance to be
  covered, test to see if correct direction)

17
Program versus Algorithm

• Program is
• Specific language (C, JAVA, C)
• Specific circumstance
• Eg. Algorithm for addition,
• Program in JAVA to add entered numbers(input)

18
Algorithm example on board