
112 Knowledge Discovery from Data Streams
order to focus on recent or old behaviors in the stream following application
specific constraints. A bias function f(r, t) associated with the r
th
data point
of the stream at the time of arrival of the t
th
point is proportional to the prob-
ability p(r, t) of the r
th
point belonging to the reservoir at the time of arrival
of the t
th
point. The use of a bias function guarantees that recent points ar-
riving over the stream have higher probabilities to be inserted in the reservoir.
However, it is still an open problem to determine if maintenance algorithms
can be implemented in one pass but the author in Aggarwal ...