index 59f9d576578c35be53ec14532988e4a168067e6a..702d34e3f8044e8e5625dc5adc19b4cf92fb1c57 100644 (file)
Clause reduction (planner/optimizer)
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-Applying the functional dependencies is fairly simple - given a list of
+Applying the functional dependencies is fairly simple: given a list of
equality clauses, we compute selectivities of each clause and then use the
degree to combine them using this formula
P(a=?,b=?) = P(a=?) * (d + (1-d) * P(b=?))
-Where 'd' is the degree of functional dependence (a=>b).
+Where 'd' is the degree of functional dependency (a => b).
With more than two equality clauses, this process happens recursively. For
-example for (a,b,c) we first use (a,b=>c) to break the computation into
+example for (a,b,c) we first use (a,b => c) to break the computation into
- P(a=?,b=?,c=?) = P(a=?,b=?) * (d + (1-d)*P(b=?))
+ P(a=?,b=?,c=?) = P(a=?,b=?) * (e + (1-e) * P(c=?))
-and then apply (a=>b) the same way on P(a=?,b=?).
+where 'e' is the degree of functional dependency (a,b => c); then we can
+apply (a=>b) the same way on P(a=?,b=?).
Consistency of clauses