Problem specificity: flexibility of publication & subscription
No pre-defined schema for events
- (category, book), (title, Hamlet ) , (price, $20), (author, Sheakespeare)
- (category, antiques), (price, $80), (period, XIX)
Multiples values for the same attribute
- (category, {book,antiques}), (title, Hamlet), (author, Sheakespeare), (price, $100) (period, XIX)
Subscriptions apply on a subset of attributes
- notify me of Hamlet sold for less that $20. (title = Hamlet ) & (price < $20)
- notify me of antique Hamlet editions (category = book) & (category = antiques) & (title = Hamlet )