Conjunctive Queries
Conjunctive Queries
Conjunctive Queries
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H<br />
Y<br />
Z<br />
U<br />
P<br />
V<br />
W<br />
Y<br />
Z<br />
rule 1<br />
U<br />
rule 2<br />
Y<br />
Z<br />
U<br />
rule 1<br />
0<br />
7<br />
9<br />
8<br />
6<br />
5<br />
0<br />
9<br />
6<br />
GYO-irreducible<br />
2 3 4<br />
H*= (ø,ø)<br />
GYO reduct<br />
rule 2<br />
1<br />
AternativeProcedure<br />
Definition: Anearedge(short: ear) ofahypergraph (V,E)isa<br />
hyperedge e Esuchthatoneofthefollowingconditionsholds:<br />
Hypergraph ofBCQs<br />
(1)Thereisawitnesse’ E,suchthate’ e andeach<br />
vertexfrome iseitheronlyine orine’,or<br />
(2)ehasnointersectionwithanyotherhyperedge.<br />
(C,D,E)is<br />
anear<br />
Ears<br />
Ears<br />
63<br />
64
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