/*
 * @(#)PolicyCombiningAlgorithm.java
 *
 * Copyright 2003-2004 Sun Microsystems, Inc. All Rights Reserved.
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 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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package com.sun.xacml.combine;

import com.sun.xacml.EvaluationCtx;

import com.sun.xacml.ctx.Result;

import java.net.URI;

import java.util.List;


/**
 * The base type for all Policy combining algorithms. Unlike in Rule 
 * Combining Algorithms, each policy must be matched before they're evaluated
 * to make sure they apply. Also, in combining policies, obligations must be
 * handled correctly. Specifically, no obligation may be included in the
 * <code>Result</code> that doesn't match the effect being returned. So, if
 * INDETERMINATE or NOT_APPLICABLE is the returned effect, no obligations
 * may be included in the result. If the effect of the combining algorithm
 * is PERMIT or DENY, then obligations with a matching fulfillOn effect
 * are also included in the result.
 *
 * @since 1.0
 * @author Seth Proctor
 * @author Marco Barreno
 */
public abstract class PolicyCombiningAlgorithm extends CombiningAlgorithm
{

    /**
     * Constructor that takes the algorithm's identifier.
     *
     * @param identifier the algorithm's identifier
     */
    public PolicyCombiningAlgorithm(URI identifier) {
        super(identifier);
    }

    /**
     * Combines the policies based on the context to produce some unified
     * result. This is the one function of a combining algorithm.
     * <p>
     * Note that unlike in the RuleCombiningAlgorithms, here you must
     * explicitly match the sub-policies to make sure that you should
     * consider them, and you must handle Obligations.
     *
     * @param context the representation of the request
     * @param policies the policies to combine
     *
     * @return a single unified result based on the combining logic
     */
    public abstract Result combine(EvaluationCtx context, List policies);

}