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/*******************************************************************
 * © 2023 SAP SE or an SAP affiliate company. All rights reserved. *
 *******************************************************************/
package com.sap.cds.ql.cqn.transformation;

import com.google.common.annotations.Beta;

/**
 * Transformation that determines descendants of instances that belong to a
 * recursive hierarchy.
 * 
 * The hierarchy is defined by the {@link #hierarchyReference() hierarchy
 * reference} and the {@link #hierarchyQualifier() hierarchy qualifier}.
 * 
 * The transformation takes an input set consisting of instances that belong to
 * the hierarchy. It firstly determines a subset A of the input set by
 * applying {@link #transformations() transformations} - typically
 * {@link CqnFilterTransformation filter} or {@link CqnSearchTransformation
 * search} - to the input set. Then it determines the set of descendants of
 * A that were already contained in the input set. Its output set is the
 * descendants set, {@link #keepStart() optionally} including A.
 */
@Beta
public interface CqnDescendantsTransformation extends CqnHierarchySubsetTransformation {

	@Override
	default Kind kind() {
		return Kind.DESCENDANTS;
	}
}