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Example
- notify me of Hamlet edition sold for less that $20. (title = Hamlet ) & (price < $20)
A simple solution treats each missing attributes as a « distinguished » value
- (title = Hamlet ) & (price < $20) & (authors = ?) & (category = ?)
A single event generates 2d points queries
- d is the number of event attributes values.
- (Hamlet,7,Sheak.,book) ? (?,7,Sheak,book), (?,?,?,book), (?,?,??), (Hamlet,?,Sheak,book), (Hamlet,?,?,book), … (Hamlet,7,?,?), …