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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.xerces.xni.grammars;

/**
 *  This interface specifies how the parser and the application
 * interact with respect to Grammar objects that the application
 * possesses--either by having precompiled them or by having stored them
 * from a previous validation of an instance document.  It makes no
 * assumptions about the kind of Grammar involved, or about how the
 * application's storage mechanism works.
 *
 * The interaction works as follows:
 * 

 * When a validator considers a document, it is expected to request
 * grammars of the type it can handle from this object using the
 * retrieveInitialGrammarSet method. 
 * If it requires a grammar
 * not in this set, it will request it from this Object using the
 * retrieveGrammar method.  
 *  After successfully validating an
 * instance, the validator should make any new grammars it has compiled
 * available to this object using the cacheGrammars
 * method; for ease of implementation it may make other Grammars it holds references to as well (i.e., 
 * it may return some grammars that were retrieved from the GrammarPool in earlier operations). 
 
 
 *
 * @author Neil Graham, IBM
 * @version $Id: XMLGrammarPool.java 447245 2006-09-18 05:22:10Z mrglavas $
 */

public interface XMLGrammarPool {

    // we are trying to make this XMLGrammarPool work for all kinds of
    // grammars, so we have a parameter "grammarType" for each of the
    // methods. 

    /**
     *  retrieve the initial known set of grammars. this method is
     * called by a validator before the validation starts. the application 
     * can provide an initial set of grammars available to the current 
     * validation attempt. 
     * @param grammarType the type of the grammar, from the
     *  org.apache.xerces.xni.grammars.Grammar interface.
     * @return the set of grammars the validator may put in its "bucket"
     */
    public Grammar[] retrieveInitialGrammarSet(String grammarType);

    /** 
     * return the final set of grammars that the validator ended up
     * with.  
     * This method is called after the
     * validation finishes. The application may then choose to cache some
     * of the returned grammars. 
     * @param grammarType the type of the grammars being returned;
     * @param grammars an array containing the set of grammars being
     *  returned; order is not significant.
     */
    public void cacheGrammars(String grammarType, Grammar[] grammars);

    /** 
     *  This method requests that the application retrieve a grammar
     * corresponding to the given GrammarIdentifier from its cache.
     * If it cannot do so it must return null; the parser will then
     * call the EntityResolver.  An application must not call its
     * EntityResolver itself from this method; this may result in infinite
     * recursions.
     * @param desc The description of the Grammar being requested.
     * @return the Grammar corresponding to this description or null if
     *  no such Grammar is known.
     */
    public Grammar retrieveGrammar(XMLGrammarDescription desc);

    /**
     * Causes the XMLGrammarPool not to store any grammars when
     * the cacheGrammars(String, Grammar[[]) method is called.
     */
    public void lockPool();

    /**
     * Allows the XMLGrammarPool to store grammars when its cacheGrammars(String, Grammar[])
     * method is called.  This is the default state of the object.
     */
    public void unlockPool();

    /**
     * Removes all grammars from the pool.
     */
    public void clear();
} // XMLGrammarPool