uk.ac.bbk.dcs.automed.qproc.optimise.optimisers
Class RelationSKJEliminator

java.lang.Object
  uk.ac.bbk.dcs.automed.qproc.optimise.optimisers.RelationSKJEliminator

public class RelationSKJEliminator
extends java.lang.Object

This class removes self-join of relations over their key arising from the AutoMed relational model encoding For example, [{k1,n,m}|{p1,n}<-[{{k1,..,kn},a1}|{k1,..,kn,a1,a2}<-<>]; {p2,m}<-[{{k1,..,kn},a2}|{k1,..,kn,a1,a2}<-<>]; p1 = p2] becomes: [{{k1,...,kn},a1,a2}|{k1,..,kn,a1,a2}<-<>] Although table <> may contain several key attributes, we assume that {p1,n} and {p2,m} will be pair The steps for the simplification are: 1. Method isRelTableStrComp checks if a comp is a RelTableStrComp which is generated by AutoMed relational wrappers, like: [{{k1,..,kn},ai}|{k1,..,kn,a1,a2,...,an}<-S1:<>] 2. Methods unifyVarInRelTableStrComp and mappingVarsInRelTableStrGen rename vars in all RelTableStrComp in the comprehension, and map the vars in the main comp to the vars in the sub RelTableStrComp: [h|{p11,a11,a12,...,a1n} <- [{{k1,...,kp},ai}|{k1,...,kp,a1,...,am}<-<>]; {p21,a21,a22,...,a2n} <- [{{k1,...,kq},aj}|{k1,...,kq,a1,...,an}<-<>]; ... P] changes into: [h|{p11,a11,a12,...,a1n} <- [{{$un_R1_k1_1,...,$un_R1_kp_1},$un_R1_ai_1}| {$un_R1_k1_1,...,$un_R1_kp_1,$un_R1_a1_1,...,$un_R1_am_1}<-<>]; {p21,a21,a22,...,a2n} <- [{{$un_R2_k1_2,...,$un_R2_kq_2},$un_R2_aj_2}| {$un_R2_k1_2,...,$un_R2_kq_2,$un_R2_a1_2,...,$un_R2_an_2}<-<>]; ... P] 3. Method isTwoEquivalentKey checks self-Key-Join generators which are generated from the same RelTableStrComp and having the equator between their keys [h|{p11,a11}<-RelTableStrComp1;{p12,a12}<-RelTableStrComp1;...;{p1n,a1n}<-RelTableStrComp1; p11=p12;p12=p13;...;p1i=p1n;...;P] 3. This step removes self-Key-Join generators: all generators are inserted into an ArrayList, genList, and for each element in the list, if there is a self-Key-Join gen within it, remove the selfKeyJoin gen 4. Method replaceVarValWithMap replaces vars in h and P with their values from varMap, which is the hashMap between the main comp vars and the vars in sub RelTableStrComp: 5. This step creates a new comp which consists of the remaining generators in the genList and unnests nested generators by replacing the current generator with the generator in its sub RelTableStrComp

Author:

Hao Fan, Lucas Zamboulis

Field Summary

protected java.util.logging.Logger

logger

Constructor Summary

RelationSKJEliminator()

Method Summary

boolean

optimise(ASG g)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

logger

protected java.util.logging.Logger logger

Constructor Detail

RelationSKJEliminator

public RelationSKJEliminator()

Method Detail

optimise

public boolean optimise(ASG g)