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RDF Storage And Inference Layer ("Sail") API.
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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.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 *******************************************************************************/
package org.eclipse.rdf4j.sail;

import java.io.File;
import java.util.List;
import java.util.function.Supplier;

import org.eclipse.rdf4j.collection.factory.api.CollectionFactory;
import org.eclipse.rdf4j.collection.factory.impl.DefaultCollectionFactory;
import org.eclipse.rdf4j.common.transaction.IsolationLevel;
import org.eclipse.rdf4j.model.ValueFactory;

/**
 * Sail (Storage And Inference Layer) is an interface for RDF storage. RDF Sails can store RDF statements and evaluate
 * queries over them. Statements can be stored in named contexts or in the null context. Contexts can be used to group
 * sets of statements that logically belong together, for example because they come from the same source. Both URIs and
 * blank nodes can be used as context identifiers.
 *
 * @author Arjohn Kampman
 */
public interface Sail {

	/**
	 * Sets the data directory for the Sail. The Sail can use this directory for storage of data, parameters, etc. This
	 * directory must be set before the Sail is {@link #initialize() initialized}.
	 *
	 * @throws IllegalStateException If this method is called when the Sail has already been initialized.
	 */
	void setDataDir(File dataDir);

	/**
	 * Gets the Sail's data directory.
	 *
	 * @see #setDataDir(File)
	 */
	File getDataDir();

	/**
	 * Initializes the Sail. Care should be taken that required initialization parameters have been set before this
	 * method is called. Please consult the specific Sail implementation for information about the relevant parameters.
	 *
	 * @throws SailException If the Sail could not be initialized.
	 * @since 2.5
	 */
	void init() throws SailException;

	/**
	 * Shuts down the Sail, giving it the opportunity to synchronize any stale data. Care should be taken that all
	 * initialized Sails are being shut down before an application exits to avoid potential loss of data. Once shut
	 * down, a Sail can no longer be used until it is re-initialized.
	 *
	 * @throws SailException If the Sail object encountered an error or unexpected situation internally.
	 */
	void shutDown() throws SailException;

	/**
	 * Checks whether this Sail object is writable, i.e. if the data contained in this Sail object can be changed.
	 */
	boolean isWritable() throws SailException;

	/**
	 * Opens a connection on the Sail which can be used to query and update data. Depending on how the implementation
	 * handles concurrent access, a call to this method might block when there is another open connection on this Sail.
	 *
	 * @throws SailException         If no transaction could be started, for example because the Sail is not writable.
	 * @throws IllegalStateException If the Sail has not been initialized or has been shut down.
	 */
	SailConnection getConnection() throws SailException;

	/**
	 * Gets a ValueFactory object that can be used to create IRI-, blank node-, literal- and statement objects.
	 *
	 * @return a ValueFactory object for this Sail object.
	 */
	ValueFactory getValueFactory();

	/**
	 * Retrieve the {@link IsolationLevel}s supported by this SAIL, ordered by increasing complexity.
	 *
	 * @return a non-empty List of supported Isolation Levels, in order of increasing complexity. Every SAIL supports at
	 *         least one {@link IsolationLevel}.
	 */
	List getSupportedIsolationLevels();

	/**
	 * Retrieves the default {@link IsolationLevel} level on which transactions in this Sail operate.
	 *
	 * @return the {@link IsolationLevel} that will be used with {@link SailConnection#begin()}, for SAIL connections
	 *         returned by {@link #getConnection()}.
	 */
	IsolationLevel getDefaultIsolationLevel();

	/**
	 * Gets a CollectionFactory that may be optimized for this store and may or may not use disk or other resources.
	 *
	 * @return a CollectionFactory
	 */
	default Supplier getCollectionFactory() {
		return DefaultCollectionFactory::new;
	}
}