Author:
Sepehr Assadi.

Abstract:
We study the classic set cover problem in the streaming model: the sets that comprise the instance are revealed one by one in a stream and the goal is to solve the problem by making one
or few passes over the stream while maintaining a sublinear space o(mn) in the input size; here m denotes the number of the sets and n is the universe size. Notice
that in this model, we are mainly concerned with the space requirement of the algorithms and hence do not restrict their computation time.

Our main result is a resolution of the space-approximation tradeoff for the streaming set cover problem: we show that any α-approximation algorithm for the set cover
problem requires Ω(mn^{1/α}) space, even if it is allowed polylog(n) passes over the stream, and even if the sets are arriving in a random order in the stream.
This space-approximation tradeoff matches the best known bounds achieved by the recent algorithm of Har-Peled et al. (PODS 2016) that requires only O(α) passes over the stream
in an adversarial order, hence settling the space complexity of approximating the set cover problem in data streams in a quite robust manner. Additionally, our approach yields
tight lower bounds for the space complexity of (1−ε)-approximating the streaming maximum coverage problem studied in several recent works.

Conference version:
[PDF]
Presentation slides:
[PDF]