Pick content
Match content with user intent.
Long term objective: Maximize user experience. Short term, meterable, objective: Maximize click-through rates (CTR) subject to constraints (Eg: don’t show porn).
Pick content-layout
Maximize ad revenue
Match advertisements with content
\tbc
Data
Inventory often expires: Eg: news articles; cause: user fatigue.
Data is huge.
User responses
Responses are multivariate: click rates, ratings etc.. Negative responses very noisy.
Online experimentation
Comparing models tough without experiments.
Usually allowed on a fraction of visits. A generalization of multi-armed bandits: See Game theory ref.