conf as usual slipped into the fading days of 2009. For me, it started with Andrei Broder's tutorial on Sunday. (Alas, I missed Nikhil's and Tim's tutorials on Saturday). At the basic level, there is a "mapping":(user queries, context, content of web pages) \rightarrow (suitable ads or creatives),
that is a challenge in Internet Ads, and Andrei's tutorial was a flourishing, flowing view of this mapping, mainly as a Information Retrieval (IR) task. Some specific topics beyond the tf-idf like measures and precision-recall curves included (a) looking at ads -- creatives/URLs/bid phrases -- as documents for IR, (b) using taxonomy to capture context for content match, (c) graphical ad selection by looking at this mapping as a recommendation function, (d) bandit variations with taxonomy for new ads, and (e) classification, in particular for rare queries, across multiple languages. These ideas are published in a slew of papers in WWW, KDD, SIGIR confs. Andrei's audience showed an yearning for novelty, and he indulged them with describing challenges in mobile ads, ads over IPTV, VDP newspapers etc. He mentioned the Webscope program
to share data with academia, including some data on mapped (query, ad) pairs.
On Monday, I gave a talk on my AdX model for Ad exchanges
. It is difficult to communicate how the many decisions you make every week ultimately determines the overall system that audience get to see, and users get to play. I chose to talk about 3 technical results, one each on auction, online optimization and crypto, so people get a little bit of new things in their area of expertise, and a little peek into new things in other areas. I had a bunch of questions over the following two days.
- Why not sell bulk impressions? AdX trades on individual impressions. More sophisticated instruments -- like bulk impressions, futures, derivatives, whatever -- may get traded on top of this primitive.
- Why do we need AdX, and why will traders come to AdX? Publishers come for liquidity and better prices. Peyton Young, ever sharp, asked one question over dinner: what is the information that goes from AdX to ad networks. Advertisers come to AdX to potentially influence ad experience across multiple websites easily.
- Aren't there complex pathways from advertisers to AdX via multiple interacting ad networks? Yes. In some exchanges like RightMedia, these relationships are endogenized and leads to sophisticated graph problems to determine suitable bids for each impression. In the AdX model, these are exogenized so we can focus on the game theory between AdX and ad networks, or between AdXs.
- How to deal with currency changes? This is not a question of $s vs Euros, but as marketplaces get sophisticated, parties have many different payment schemes (pay per impressions, clicks, conversions, or pay flat fee or for bulk etc), these have to compiled down to per-impression bid in AdX, and this involves taking some statistical risk; it is a nice open problem how to manage this risk. Finally,
- Why do you work on AdX and why not work on exchanges in general instead of ad exchanges? It sounds silly, but I want to change the display ads business, and I think AdX will change the display ads business to make it more transparent, robust. In Applied Algorithms research, you have to believe in a goal beyond the theorems.
On Tuesday, Peyton Young gave a very interesting talk on adaptive learning rules in complex systems of agents. As an aside, he like many Economists is a swingman, being able to talk macro, micro, math, policy and everything else with insight. His talk was a series of "experiments" in which agents have a state comprising a benchmark of what they did and an aspiration function, and based on choosing to experiment, can change their benchmark. In one version, agents experiment based on mood in an interactive trial and error way. In yet another version, agents have logit response to neighbors' actions (a la some of Larry Blume's work). He showed the connection between these rules and well-known games from weakly acyclic games to interdependent games and spatial potential games. In each case, under some mild conditions, the Nash equilibrium is in some amount of experimentation. I really liked the spirit of this talk, and would have liked to see more, perhaps connection to the bandit literature.