Synonyms
Logical window = Time-based window; Physical window = Tuple-based windows
Definition
Windows were introduced as part of SQL:1999 OLAP functions. For instance, given a sequence of bids, it is possible to use the following SQL:2003 statement to find the last 40 offers (the current offer and the previous 39) for item 0021:
SELECT itemID, avg(Offer)
OVER(ROWS 39 PRECEDING ORDER BY TIME)
FROM BIDS
WHERE ItemID = 0021
When BIDS is instead a data stream, the “ORDER BY TIME” clause becomes redundant, and clauses such as “FOLLOWING” are often not supported in continuous query languages. However, these languages still provide a “PARTITION BY” clause (or the more traditional “GROUP BY” clause), whereby a user can specify that the average of the last 40 offers must be computed for all items, not just item 0021. In addition to entailing powerful and flexible analytical queries on ordered sequences and time series, as in databases, windows on data streams play the key role of synopsesand...
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Li J, et al. Semantics and evaluation techniques for window aggregates in data streams. In: Proceedings of the ACM SIGMOD International Conference on Management of Data; 2005. p. 311–22.
Maier D, Tucker PA, Garofalakis M. Filtering, punctuation, windows and synopses. In: Chaudhry N, Shaw K, Abdelguerfi M, editors. Stream data management, vol. 30. Dordrecht: Kluwer; 2005. p. 35–56.
Bai Y, et al. A data stream language and system designed for power and extensibility. In: Proceedings of the 15th ACM International Conference on Information and Knowledge Management; 2006. p. 337–46.
Ghanem T, et al. Incremental evaluation of sliding-window queries over data streams. IEEE Trans Knowl Data Eng. 2007;19(1):57–72.
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Zaniolo, C. (2018). Windows. In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_469
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DOI: https://doi.org/10.1007/978-1-4614-8265-9_469
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