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/*******************************************************************************
* Copyright (c) 2010-2016, Gabor Bergmann, IncQueryLabs Ltd.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0 which is available at
* http://www.eclipse.org/legal/epl-v20.html.
*
* SPDX-License-Identifier: EPL-2.0
*******************************************************************************/
package tools.refinery.viatra.runtime.matchers.psystem.aggregations;
import java.util.Collection;
import java.util.stream.Stream;
import tools.refinery.viatra.runtime.matchers.aggregators.ExtremumOperator;
/**
* A single column aggregator is used to incrementally compute the aggregate of a multiset of values according to an aggregator operator.
*
* <p> The operator provides two methods of computation: <ul>
* <li>Stateless aggregation of an explicit multiset, provided by {@link #aggregateStatelessly(Collection)}.</li>
* <li>Incremental aggregation, provided by {@link #createNeutral()}, {@link #update(Object, Object, boolean)}, {@link #isNeutral(Object)}, {@link #getAggregate(Object)}.
* </ul>
*
* <p> In case of incremental computation, the aggregable multiset is conceptual; it is not represented by an explicit Collection<Domain> object, but its update operations are tracked.
*
* <p> In case of incremental computation, internal results, potentially distinct from the final aggregate result, may be stored in a helper data structure called <b>accumulator</b>.
* The goal of this distinction is that the final result may not be sufficient for incremental updates (see e.g. {@link ExtremumOperator}).
*
* @author Gabor Bergmann
*
* @param <Domain> the type of elements to be aggregated.
* @param <Accumulator> the type used to store the interim results of the aggregate computation,
* that may be incrementally refreshed upon updates to the multiset, and that can easily yield the final result.
* @param <AggregateResult> the type of the final result of the aggregation to be output.
*
* @since 1.4
*/
public interface IMultisetAggregationOperator<Domain, Accumulator, AggregateResult> {
/**
* A textual description of the operator.
*/
String getShortDescription();
/**
* A name or identifier of the operator.
*/
String getName();
/**
* @return the neutral element, i.e. the interim result of aggregating an empty multiset.
*/
Accumulator createNeutral();
/**
* @return true if the interim result is equivalent to the neutral element, as if there are no values in the multiset.
* Must return true if the multiset is empty.
*/
boolean isNeutral(Accumulator result);
/**
* @return an updated intermediate result,
* changed to reflect that a given object was added to / removed from the multiset
* (as indicated by the parameter isInsertion)
*/
Accumulator update(Accumulator oldResult, Domain updateValue, boolean isInsertion);
/**
* @return the aggregate result obtained from the given intermediate result.
* May be null to indicate that the current multiset cannot be aggregated (e.g. 0 elements have no minimum).
*/
AggregateResult getAggregate(Accumulator result);
/**
* Calculates the aggregate results from a given stream of values; all values are considered as inserted
* @return the aggregate result, or null if no result can be calculated (e.g. because of an empty stream)
* @since 2.0
*/
AggregateResult aggregateStream(Stream<Domain> stream);
/**
* Clones the given accumulator (with all its internal contents).
*/
default Accumulator clone(Accumulator original) {
throw new UnsupportedOperationException();
}
/**
* Combines the given aggregate result and accumulator into a single aggregate result.
*/
default AggregateResult combine(AggregateResult left, Accumulator right) {
throw new UnsupportedOperationException();
}
default boolean contains(Domain value, Accumulator accumulator) {
throw new UnsupportedOperationException();
}
/**
* Pretty prints the contents of the given accumulator.
*/
default String prettyPrint(final Accumulator accumulator) {
return accumulator.toString();
}
}
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