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We give a language-independent characterization of the expressive power of the relational algebra on finite sets of source-target relation instance pairs. The associated decision problem is shown to be co-graph-isomorphism hard and in co NP. The main result is also applied in providing a new characterization of the generic relational queries.
Knowledge and Data Engineering, IEEE Transactions on (Volume:21 , Issue: 6 )
Date of Publication: June 2009