/*******************************************************************************
 * 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 <b>AND</b>,
	 * <b>OR</b>, 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 <b>SELECT</b>.
	 */
	CLAUSE,

	/**
	 * Indicates the identifier is used to complement an expression, it is not required for creating
	 * an expression. Examples are <b>AS</b> or <b>OUTER</b>.
	 */
	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 <b>x MEMBER y</b>.
	 */
	COMPOUND_FUNCTION,

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

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