Class ExecOpMultiRequest

java.lang.Object

se.liu.ida.hefquin.engine.queryplan.executable.impl.ops.BaseForExecOps

se.liu.ida.hefquin.engine.queryplan.executable.impl.ops.NullaryExecutableOpBase

se.liu.ida.hefquin.engine.queryplan.executable.impl.ops.ExecOpMultiRequest

All Implemented Interfaces:

StatsProvider, ExecutableOperator, NullaryExecutableOp

public class ExecOpMultiRequest
extends NullaryExecutableOpBase

Issues the same request (same query pattern) at multiple federation members and processes their respective responses, all in parallel. Every solution mapping obtained via each such response is extended with a binding for the given service variable and, then, passed on to the output. Specifically, the service variable is assigned to the service URI of the corresponding federation member.

In cases in which the query pattern of this request mentions the service variable, the implementation checks that the solution mappings obtained via a response bind this variable to the service URI of the federation member from which the response was received. As an additional optimization, to avoid even receiving the solution mappings that will be filtered out by this check, the implementation tries to add the following member-specific FILTER condition into the requests (which is possible only for federation members that support requests with FILTER conditions; e.g., SPARQL endpoints):

(! BOUND(?s)) || (?s = _uri_)

where ?s is the service variable and _uri_ is the service URI of the federation member.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected class	ExecOpMultiRequest.MyResponseProcessor1	This response processor can be used for cases in which the service variable of this operator is not in the request of this operator and, thus, does not show up in the solution mappings obtained via this request.
protected class	ExecOpMultiRequest.MyResponseProcessor2	This response processor can be used for cases in which the service variable of this operator is also in the request of this operator, which means that the solution mappings obtained via this request may already have a binding for this variable and, thus, need to be checked for compatibility.

Field Summary

Fields

Modifier and Type	Field	Description
protected final Set<FederationMember>	fms
protected int	numberOfRequestsIssued
protected final SPARQLRequest	req
protected final org.apache.jena.sparql.core.Var	serviceVar
protected org.apache.jena.sparql.expr.ExprVar	serviceVarForExpressions
protected final boolean	serviceVarIsInPattern
protected org.apache.jena.sparql.expr.Expr	subExpr1

Fields inherited from class se.liu.ida.hefquin.engine.queryplan.executable.impl.ops.NullaryExecutableOpBase

timeAtExecEnd, timeAtExecStart

Fields inherited from class se.liu.ida.hefquin.engine.queryplan.executable.impl.ops.BaseForExecOps

collectExceptions, mayReduce, qpInfo

Constructor Summary

Constructors

Constructor	Description
ExecOpMultiRequest(SPARQLRequest req, org.apache.jena.sparql.core.Var serviceVar, Set<FederationMember> fms, boolean collectExceptions, QueryPlanningInfo qpInfo)

Method Summary

Modifier and Type	Method	Description
protected void	_execute(IntermediateResultElementSink sink, QueryProcContextExt ctx)	Implementations of this function need to execute the algorithm of this operator and send the result elements (if any) to the given sink.
protected ExecutableOperatorStatsImpl	createStats()
protected SPARQLRequest	makeRequestMemberSpecific(FederationMember fm)	Returns a request with a graph pattern that is created by extending the graph pattern of req with a FILTER of the form (!
protected void	recordException(String msg, Exception cause)
void	resetStats()

Methods inherited from class se.liu.ida.hefquin.engine.queryplan.executable.impl.ops.NullaryExecutableOpBase

execute, getStats

Methods inherited from class se.liu.ida.hefquin.engine.queryplan.executable.impl.ops.BaseForExecOps

getExceptionsCaughtDuringExecution, getQueryPlanningInfo, mayReduce, recordExceptionCaughtDuringExecution

Methods inherited from class java.lang.Object

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

Methods inherited from interface se.liu.ida.hefquin.engine.queryplan.executable.ExecutableOperator

getExceptionsCaughtDuringExecution, getQueryPlanningInfo, mayReduce

Field Details

req

protected final SPARQLRequest req

serviceVar

protected final org.apache.jena.sparql.core.Var serviceVar

fms

protected final Set<FederationMember> fms

serviceVarIsInPattern

protected final boolean serviceVarIsInPattern

serviceVarForExpressions

protected org.apache.jena.sparql.expr.ExprVar serviceVarForExpressions

subExpr1

protected org.apache.jena.sparql.expr.Expr subExpr1

numberOfRequestsIssued

protected int numberOfRequestsIssued

Constructor Details

ExecOpMultiRequest

public ExecOpMultiRequest(SPARQLRequest req,
 org.apache.jena.sparql.core.Var serviceVar,
 Set<FederationMember> fms,
 boolean collectExceptions,
 QueryPlanningInfo qpInfo)

Method Details

_execute

protected void _execute(IntermediateResultElementSink sink,
 QueryProcContextExt ctx)
                 throws ExecOpExecutionException

Description copied from class: NullaryExecutableOpBase

Implementations of this function need to execute the algorithm of this operator and send the result elements (if any) to the given sink. If an exception occurs during this process, then this exception needs to either be collected or be thrown, depending on whether BaseForExecOps.collectExceptions is set to true.

Specified by:

_execute in class NullaryExecutableOpBase

Throws:

ExecOpExecutionException

makeRequestMemberSpecific

protected SPARQLRequest makeRequestMemberSpecific(FederationMember fm)

Returns a request with a graph pattern that is created by extending the graph pattern of req with a FILTER of the form (! BOUND(?s)) || (?s = _uri_) where ?s is the service variable (see serviceVar) and _uri_ is the service URI of the given federation member. If the given federation member does not support the extended graph pattern, null is returned.

resetStats

public void resetStats()

Specified by:

resetStats in interface StatsProvider

Overrides:

resetStats in class NullaryExecutableOpBase

createStats

protected ExecutableOperatorStatsImpl createStats()

Overrides:

createStats in class NullaryExecutableOpBase

recordException

protected void recordException(String msg,
 Exception cause)