Database Theory Column Victor Vianu Query Languages for Bags Expressive Power and Complexity 1
نویسندگان
چکیده
One of the characteristics of advanced database systems is that they must handle data which no longer ts the traditional relational style. The present column summarizes recent results on one such extension, where databases handle bags (multisets) rather than just sets. The results illustrate an important research direction in Database Theory. Abstract Most database theory focused on investigating databases containing sets of tuples. In practice databases often implement relations using bags, i.e. sets with duplicates. In this paper we study how database query languages are aaected by the use of duplicates. We consider query languages that are simple extensions of the (nested) relational algebra, and investigate their resulting expressive power and complexity.
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