Chase (algorithm): Difference between revisions

Revision as of 02:27, 2 August 2019

Revision as of 16:50, 6 March 2020

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The goal for this test is to use the given ''F'' to prove that ''t'' = (''a'', ''b'', ''c'', ''d'') is really in ''R''. To do so, the tableau can be chased by applying the FD’s in ''F'' to equate symbols in the tableau. Final tableau with a row that is the same as ''t'' implies that any tuple ''t'' in the join of the projections is actually a tuple of ''R''.

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To perform the chase test, first decompose all FD’s in ''F'' so each FD has a single attribute on the right hand side of the "arrow". ''F'' remains unchanged because all of its FD'sFDs already hashave a single attribute on the right hand side. ''F'' = {''A''→''B'', ''B''→''C'', ''CD''→''A''}.

When equating two symbols, if one of them is unsubscripted, make the other be the same so that the final tableau can have a row that is exactly the same as ''t'' = (''a'', ''b'', ''c'', ''d''). Also, if both have their own subscript, change either to be the other. However, to avoid confusion, all of the occurrences should be changed.

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