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/*******************************************************************************
 * Copyright (c) 2006, 2013 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation
 *
 ******************************************************************************/
package org.eclipse.persistence.jpa.jpql.parser;

/**
 * A role describes the purpose of the JPQL identifier.
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 */
public enum IdentifierRole {

	/**
	 * Indicates the identifier aggregates two expressions together. The identifiers are AND,
	 * OR, and the arithmetic operators.
	 */
	AGGREGATE,

	/**
	 * Indicates the identifier is used to create a clause. They are the root of a portion of the
	 * query. An example is SELECT.
	 */
	CLAUSE,

	/**
	 * Indicates the identifier is used to complement an expression, it is not required for creating
	 * an expression. Examples are AS or OUTER.
	 */
	COMPLEMENT,

	/**
	 * Indicates the identifier is a kind of function, it does not return a value but it is used to
	 * perform some operation over an expression. The expression can have an expression before and
	 * after but it's not used to aggregate those two expression. An example is x MEMBER y.
	 */
	COMPOUND_FUNCTION,

	/**
	 * Indicates the identifier is used to create a function, it has some parameters and returns a
	 * value. An example is ABS(x), usually the identifier has some values encapsulated with
	 * parenthesis.
	 * 
	 * Note: TRUE, FALSE, NULL, CURRENT_DATE, CURRENT_TIME,
	 * CURRENT_TIMESTAMP are considered functions.
	 */
	FUNCTION,

	/**
	 * Indicates the identifier is not part of the language but it has been reserved for future use.
	 * The identifiers are BIT_LENGTH, CHAR_LENGTH, CHARACTER_LENGTH,
	 * POSITION, and UNKNOWN.
	 */
	UNUSED
}