1. 9 Algorithms: Indexing
Now where did I put that?

2. Algorithms
Algorithm : Step by step instructions used to solve a problem

3. Algorithms
Algorithm 1 :
Add the numbers

4. Algorithms Algorithm 1 : Algorithm 2: Add the numbers
Add each digit, carry if a column is over 10

5. Algorithms Algorithm 1 : Algorithm 2: Add the numbers
Add each digit, carry if a column is over 10

6. Algorithms Algorithm 3: Start with the rightmost column
Add the numbers in the column
If the total is less than ten, write it below that column
If the total is ten or more, write the 1's digits below that column and write a 1 above the next column to the left
Move to the next column to the left
If there are any numbers in it, go to step 2
If there are no numbers in the column, you are done

7. Algorithms Need to be mechanically executable
No intuition or guesswork
Ability to use an algorithm does not require or imply knowledge

8. Algorithms Need to be mechanically executable
Need to be precise & detailed
What is precise?
Do I have to explain how to add two single digits numbers?
Do I have to explain columns?
Do I have to explain left and right?

9. Finding Information How do I find a webpage? Catalog based navigation:
Hard to scale

10. Finding Information
Keyword search

11. Finding Information 2 part problem Identifying matches
Identifying best matches

12. Indexing the Web
Web "spiders": Programs that explore the web

13. Web Page Contents Three simple web pages:
What algorithm could answer query "cat"

14. How Do We Find Things?
How do I find ebay in 9 Algorithms book?

15. Indexing
A book index:

16. Web Page Contents
Three simple web pages:
A basic index:

17. What can we do?
What algorithm could answer query "cat"

18. What can we do? What algorithm could answer query "cat"
Why is ordering important?

19. What can we do?
What algorithm could answer query cat dog

20. What can we do? Can we answer the query "cat sat" ?
"cat sat" vs cat sat

21. Word Indexes
Web pages with numbered words:

22. Word Indexes
Web pages with numbered words:
Page-Word index

23. Word Indexes
How can we now answer these queries? "cat sat" "the mat" "a cat"

24. Word Indexes
How can we now answer these queries? "cat sat" "the mat" "a cat" no match

25. Ranking
Which page is the best source for malaria?

26. Ranking Absolute word location can guide ranking
Which page is the best source for malaria?

27. Ranking
Which page is the best source for causes of malaria?

28. Ranking Relative word location can guide ranking
Which page is the best source for causes of malaria?

29. Metadata
Metadata : data about the data

30. Structured Information
Simplified HTML (web) page

31. Structured Information
Simplified HTML (web) page
What pages have "cat" in the title?

32. Not just for the web
Operating systems, databases, etc…

33. Search as Metaphor
Search displacing/complementing "desktop" as interface metaphor

34. Changes
Significantly large changes in quantity produce a change quality