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The Federation SAIL allows multiple datasets to be virtually combined into a single dataset. The Federation SAIL combines multiple RDF stores that may exist on a remote server or are embedded in the same JVM. The Federation uses query optimizations to distribute sections of the query to different members based on the data contained in each of the members. These results are then joined together within the federation to provide the same result as if all the data was co-located within a single repository.

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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *******************************************************************************/
package org.eclipse.rdf4j.sail.federation;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author James Leigh
 */
public class PrefixHashSet {

	private int length = Integer.MAX_VALUE; // NOPMD

	private final Map> index = new HashMap<>();

	public PrefixHashSet(Iterable values) {
		for (String value : values) {
			if (value.length() < length) {
				length = value.length();
			}
		}
		for (String value : values) {
			String key = value.substring(0, length);
			List entry = index.get(key);
			if (entry == null) {
				index.put(key, entry = new ArrayList<>()); // NOPMD
			}
			entry.add(value.substring(length));
		}
	}

	public boolean match(String value) {
		boolean result = false;
		if (value.length() >= length) {
			String key = value.substring(0, length);
			List entry = index.get(key);
			if (entry != null) {
				result = matchValueToEntry(value, entry);
			}
		}
		return result;
	}

	private boolean matchValueToEntry(String value, List entry) {
		boolean result = false;
		String tail = value.substring(length);
		for (String prefix : entry) {
			if (tail.startsWith(prefix)) {
				result = true;
				break;
			}
		}
		return result;
	}

	@Override
	public String toString() {
		return index.toString();
	}
}