Content deleted Content added
→Example: Character_group X moving pages 1* Tag: Reverted |
rm sig |
||
| (One intermediate revision by one other user not shown) | |||
Line 9:
The chase can be done by drawing a tableau (which is the same formalism used in [[tableau query]]). Suppose ''R'' has [[attribute (computing)|attributes]] ''A, B, ...'' and components of ''t'' are ''a, b, ...''. For ''t<sub>i</sub>'' use the same letter as ''t'' in the components that are in S<sub>''i''</sub> but subscript the letter with ''i'' if the component is not in S<sub>''i''</sub>. Then, ''t<sub>i</sub>'' will agree with ''t'' if it is in S<sub>''i''</sub> and will have a unique value otherwise.
The chase process is [[confluence (rewriting system)|confluent]]. There exist implementations of the chase algorithm,<ref>[[Michael Benedikt (computer scientist)|Michael Benedikt]], [[George Konstantinidis]], [[Giansalvatore Mecca]], [[Boris Motik]], [[Paolo Papotti]], [[Donatello Santoro]], [[Efthymia Tsamoura]]: ''Benchmarking the Chase''. In Proc. of PODS, 2017.</ref> some of them are also open-source.<ref>{{cite web |url=https://github.com/donatellosantoro/Llunatic |title=The Llunatic Mapping and Cleaning Chase Engine|date=6 April 2021}}</ref>
==Example==
Line 66:
|}
At this point, notice that the third row is (''a'', ''b'', ''c'', ''d'') which is the same as ''t''. Therefore, this is the final tableau for the chase test with given ''R'' and ''F''. Hence, whenever ''R'' is projected onto S<sub>1</sub>, S<sub>2</sub> and S<sub>3</sub> and rejoined, the result is in ''R''. Particularly, the resulting tuple is the same as the tuple of ''R'' that is projected onto {''B'', ''C'', ''D''}.
== References ==
| |||