Abstract
We define a new operator, decomposition projection, and show that extended projection is a precise generalization of decomposition projection with respect to unnesting, and that null-extended projection is a precise generalization of decomposition projection with respect to unnesting and PNF possibility function POSS.
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Roth, M.A., Korth, H.F., Silberschatz, A.: Null values in nested relational databases. Acta Inf.26, 615–642 (1989)
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Roth, M.A., Korth, H.F. & Silberschatz, A. Addendum to Null values in nested relational databases. Acta Informatica 28, 607–610 (1991). https://doi.org/10.1007/BF01463949
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DOI: https://doi.org/10.1007/BF01463949