  We consider online competitive algorithms for the problem of collecting
weighted items from a dynamic set S, when items are added to or deleted from S
over time. The objective is to maximize the total weight of collected items. We
study the general version, as well as variants with various restrictions,
including the following: the uniform case, when all items have the same weight,
the decremental sets, when all items are present at the beginning and only
deletion operations are allowed, and dynamic queues, where the dynamic set is
ordered and only its prefixes can be deleted (with no restriction on
insertions). The dynamic queue case is a generalization of bounded-delay packet
scheduling (also referred to as buffer management). We present several upper
and lower bounds on the competitive ratio for these variants.
