Announcements

• WiCS Dinner Tonight at Gates 403

Plan for Today

• Recall: requests go to a server, which returns a response
• Today: how do servers figure out what information to return?
  • Google
  • Facebook
  • Displaying Ads

Information Storage: Databases

• One strength of computers is their ability to store and process information
• Information is stored in databases
• Like a giant Excel sheet, but with lots of rows
• Usually can't "see" all the data - choose certain columns at a time, or filter out rows with certain features
  • Example: I want to send an email to all users in North America who last logged in between 5 and 7 days ago and who have an outstanding friend request
• Basic Idea: companies store a lot of information, then responses involve searching the saved information based on the request
• Come back Thursday!

Power of Data

• Talk with a neighbor: what sorts of data do you think your favorite websites store?

Power of Data

• A good rule of thumb: every click, view, and even mouse hover is recorded and stored
• Tracking this kind of data can be very powerful
• Are people getting frustrated because a video takes too long to load?
• Which articles are the most popular?
• Which genres of movies/TV are most popular? (Netflix is phenomenal at this)

Google: Getting Information

• Indexes the internet
• "Spiders" "crawl" the internet (Google calls them "Googlebots")
• Start on a page, index that page, follow all outbound links
• Store all the information in a database
  • Contains info about the words pages contain

Google: Evaluating Relevance

• Request includes search terms
• Need to derive meaning from order of terms (Natural Language Processing)
• Search all the indexed websites
• Look for terms and their synonyms; terms in the title are better
• PageRank: a measure of how "important" a website is
  • Sort of like how academic papers work: being cited by lots of papers is better, and being cited by other important papers is better

Google Search: Recap

Facebook: Storing Friends

• Social Network: people are connected to each other through friendships
• Called a graph in CS
  • nodes = people
  • edges = friendships
• Other uses of graphs: the Internet, road networks, disease outbreaks, company hierarchies

Facebook as a Network

• Friendship Paradox: your friends have more friends on average than you do
• Triadic Closure: how People You May Know works
• Degrees of Separation and (Kevin) Bacon number

Storing Other Information

• Stores likes, comments, posts, live videos, messages, etc.
• Big idea: give IDs to users and each type of interaction
• Tables in a database for each of these, linked by IDs
• News Feed algorithm: get the content from each of your friends, attempt to rank using relevance, popularity, and recentness

Internet Advertisements

• Some target certain types of individuals: Facebook
• Some target certain search terms: Google
• Some track your internet search history through ad-tracking using third-party cookies that are shared across websites
• In general, ad campaigns have a budget and a bid per view or bid per click; ordering on a page and which ads are visible are based on bids

Recap

• Companies decide how to store information
• How companies prioritize information and interpret requests has a huge impact on society

Exam