uk.ac.ic.doc.rodex.qproc
Class MiniConQueryRewriter

java.lang.Object
  uk.ac.ic.doc.rodex.qproc.QueryRewriter
      uk.ac.ic.doc.rodex.qproc.MiniConQueryRewriter

Direct Known Subclasses:

MiniConQueryRewriterAdaptive, MiniConQueryRewriterNonConjunctive

public class MiniConQueryRewriter
extends QueryRewriter

Nested Class Summary

protected class

MiniConQueryRewriter.MiniConDescription A private inner class to represent an MCD

Field Summary

protected java.util.List	mcds
protected QueryAnalyser	queryAnalyser
protected QueryAnalyser[]	viewAnalysers

Fields inherited from class uk.ac.ic.doc.rodex.qproc.QueryRewriter

_qa, query, views

Constructor Summary

MiniConQueryRewriter(ASG query, java.util.List views)
Creates a new instance of MiniConQueryRewriter given only a list of cached views

MiniConQueryRewriter(ASG query, QueryAnalyser[] viewMetadata)
Creates a new instance of MiniConQueryRewriter given a list of metadata objects of cached views

Method Summary

QueryAnalyser	analyse() Implements method in QueryWriter parent class Analyse query and view rules into head vars and sub-goals in order to prepare for the actual rewrite to take place
protected java.util.Map	checkComparisonPredicates(QueryAnalyser qa, MiniConQueryRewriter.MiniConDescription mcd) keep a mapping b/w pairs of query-view whose predicates have been checked
protected java.util.Map	checkConstants(QueryAnalyser qa, MiniConQueryRewriter.MiniConDescription mcd) Check if the current MCD support any constants in the query
protected boolean	contains(java.util.List goalSet1, java.util.List goalSet2) Check if a set of query sub-goals contains another set of sub-goals
protected java.util.List	createConjunctiveQueries(java.util.List mcds, java.util.List qSubGoals) Create the conjunctive queries from MCDs
protected java.lang.String	createQueryFromSubGoals(java.util.List subGoals)
protected QuerySubGoal	getLeastRestrictiveMapping(QuerySubGoal querySubGoal, java.util.List viewSubGoals) Check for sub-goal mapping between a query's sub-goal and a view.
protected java.util.List	getMinimumCoverage(java.util.List sharedVars, QueryAnalyser view) Check that a query contains certain variables in its head and if not it must contains all related sub-goals
QueryAnalyser	getQueryAnalyser() Return query analyser
protected java.util.List	getSharedVariables(QuerySubGoal qsg) Get all shared variables between a query and one of its sub-goal
protected void	refineConjunctiveQueries(java.util.List conjQueries, QueryRewriterResult result) Refine the conjunctive queries by, for example, removing duplicate views or sub-goals.
QueryRewriterResult	rewrite() Implements method in QueryWriter abstract parent class Rewrite query using views based on the MiniCon algorithm following a two-phase process:
protected java.util.List	subtractList(java.util.List srcList, java.util.List fromList)

Methods inherited from class uk.ac.ic.doc.rodex.qproc.QueryRewriter

getQueryRewriterInstance, getQueryRewriterInstance, getQueryRewriterInstance, getQueryRewriterInstance

Methods inherited from class java.lang.Object

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

Field Detail

queryAnalyser

protected QueryAnalyser queryAnalyser

viewAnalysers

protected QueryAnalyser[] viewAnalysers

mcds

protected java.util.List mcds

Constructor Detail

MiniConQueryRewriter

public MiniConQueryRewriter(ASG query,
                            java.util.List views)

Creates a new instance of MiniConQueryRewriter given only a list of cached views

MiniConQueryRewriter

public MiniConQueryRewriter(ASG query,
                            QueryAnalyser[] viewMetadata)

Creates a new instance of MiniConQueryRewriter given a list of metadata objects of cached views

Method Detail

analyse

public QueryAnalyser analyse()
                      throws QueryRewriterException,
                             QueryIntegrityException

Implements method in QueryWriter parent class
Analyse query and view rules into head vars and sub-goals in order to prepare
for the actual rewrite to take place

Specified by:

analyse in class QueryRewriter

Returns:

QueryAnalysre object that contains query's metadata

Throws:

QueryRewriterException

QueryIntegrityException

getQueryAnalyser

public QueryAnalyser getQueryAnalyser()

Return query analyser

Specified by:

getQueryAnalyser in class QueryRewriter

rewrite

public QueryRewriterResult rewrite()
                            throws QueryRewriterException

Implements method in QueryWriter abstract parent class
Rewrite query using views based on the MiniCon algorithm following a two-phase process:

Phase 1: For each view we check to see if there is a mapping between any of the query
subgoals and the view's. If a mapping exists and there are shared variables
in the query subgoal which are also in the query's head but not in the view's head,
a further check is carried out to find the mininum set of query sub-goals containing
the shared variables that the view need to cover.

If there are any comparison predicates in the query (e.g. >, <, = etc.) and they
are mutually consistent with those found in a view mentioned above then an MCD can be created
for that view.

Phase 2: Identify disjoint sets of MCDs found in phase 1 with each set covering all query's subgoals.
Combine MCDs in each set to produce a conjunctive rewriting of the query.
The final query re-writing is the union of all conjunctive rewritten queries.

Specified by:

rewrite in class QueryRewriter

Throws:

QueryRewriterException

getLeastRestrictiveMapping

protected QuerySubGoal getLeastRestrictiveMapping(QuerySubGoal querySubGoal,
                                                  java.util.List viewSubGoals)

Check for sub-goal mapping between a query's sub-goal and a view.

Parameters:

querySubGoal - an QuerySubGoal object in the query

viewSubGoals - a List of QuerySubGoal objects in a view

Returns:

a QuerySubGoal object for least restrictive mapping
between query_sub_goal and view_sub_goal.
Return null if no mapping exists

getSharedVariables

protected java.util.List getSharedVariables(QuerySubGoal qsg)

Get all shared variables between a query and one of its sub-goal

Returns:

List a list of sub-goals

getMinimumCoverage

protected java.util.List getMinimumCoverage(java.util.List sharedVars,
                                            QueryAnalyser view)

Check that a query contains certain variables in its head and if not it
must contains all related sub-goals

Parameters:

sharedVars - a List of shared variables to check

view - a QueryAnalyser object containing having the data structure
of the view that needs to be checked

Returns:

List a minimum list of view's sub-goals (if any) that cover

the shared variables; null if view fails to cover.

checkConstants

protected java.util.Map checkConstants(QueryAnalyser qa,
                                       MiniConQueryRewriter.MiniConDescription mcd)

Check if the current MCD support any constants in the query

Parameters:

qa - the QueryAnalyser object of the query

mcd - the MiniConQueryRewriter.MiniConDescription object found

Returns:

HashMap object for storing matches found

checkComparisonPredicates

protected java.util.Map checkComparisonPredicates(QueryAnalyser qa,
                                                  MiniConQueryRewriter.MiniConDescription mcd)

keep a mapping b/w pairs of query-view whose predicates have been checked

createConjunctiveQueries

protected java.util.List createConjunctiveQueries(java.util.List mcds,
                                                  java.util.List qSubGoals)

Create the conjunctive queries from MCDs

Parameters:

mcds - a List of MiniConQueryRewriter.MiniConDescription objects

Returns:

List list of condidate queries

refineConjunctiveQueries

protected void refineConjunctiveQueries(java.util.List conjQueries,
                                        QueryRewriterResult result)

Refine the conjunctive queries by, for example, removing duplicate views or
sub-goals. These refinements are exclusive to IQL queries

Parameters:

conjQueries - a List of conjunctive queries resulted from rewriting operation

result - the QueryRewriterResult object to update with refinements

createQueryFromSubGoals

protected java.lang.String createQueryFromSubGoals(java.util.List subGoals)
                                            throws QueryRewriterException

Throws:

QueryRewriterException

contains

protected boolean contains(java.util.List goalSet1,
                           java.util.List goalSet2)

Check if a set of query sub-goals contains another set of sub-goals

Parameters:

goalSet1 - a List of goals of the first set

goalSet2 - a List of goals of the second set

Returns:

boolean true if goalSet1 contains
goalSet2, false otherwise

subtractList

protected java.util.List subtractList(java.util.List srcList,
                                      java.util.List fromList)