In this work, we study the task of estimating the numbers of distinct and k-occurring items in a time window under the constraint of differential privacy (DP). We consider several variants depending on whether the queries are on general time windows (between times t₁ and t₂), or are restricted to being cumulative (between times 1 and t₂), and depending on whether the DP neighboring relation is event-level or the more stringent item-level. We obtain nearly tight upper and lower bounds on the errors of DP algorithms for these problems. En route, we obtain an event-level DP algorithm for estimating, at each time step, the number of distinct items seen over the last W updates with error polylogarithmic in W; this answers an open question of Bolot et al. (ICDT 2013).
@InProceedings{ghazi_et_al:LIPIcs.ITCS.2023.55, author = {Ghazi, Badih and Kumar, Ravi and Nelson, Jelani and Manurangsi, Pasin}, title = {{Private Counting of Distinct and k-Occurring Items in Time Windows}}, booktitle = {14th Innovations in Theoretical Computer Science Conference (ITCS 2023)}, pages = {55:1--55:24}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-263-1}, ISSN = {1868-8969}, year = {2023}, volume = {251}, editor = {Tauman Kalai, Yael}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2023.55}, URN = {urn:nbn:de:0030-drops-175580}, doi = {10.4230/LIPIcs.ITCS.2023.55}, annote = {Keywords: Differential Privacy, Algorithms, Distinct Elements, Time Windows} }
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