Windows

Logical window = Time-based window; Physical window = Tuple-based windows

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...

Authors and Affiliations

1. University of California-Los Angeles, Los Angeles, CA, USA

   Carlo Zaniolo

Corresponding author

Correspondence to Carlo Zaniolo .

Editors and Affiliations

1. Georgia Institute of Technology College of Computing, Atlanta, GA, USA

   Ling Liu

2. University of Waterloo School of Computer Science, Waterloo, ON, Canada

   M. Tamer Özsu

1. Department of Computer Science, Brown University, Providence, RI, USA

   Ugur Cetintemel

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