/**
 *
 *  Copyright 2005 The Apache Software Foundation or its licensors, as applicable.
 *
 *  Licensed 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.tuscany.core.context;

/**
 * An entity that provides an execution context for a runtime artifact or artifacts. A <code>Context</code> may
 * be a composite, managing child contexts or it may be an atomic, i.e. leaf, context.
 *
 * @version $Rev$ $Date$
 */
public interface Context extends EventPublisher, Lifecycle {
    /**
     * Returns the instance associated with the requested name, which may be in a atomic or composite form. Atomic (i.e.
     * leaf) contexts will return an instance associated with the service name part of the compound name, which may be
     * null.
     * <p/>
     * Composite contexts will return an instance (likely a proxy) of a contained entry point context. In this case, the
     * port name on the qualified name will correspond to the composite context name and the part name will be used to
     * retrieve the contained entry point context. The latter may be null. If the contained context is not an entry
     * point context, an exception will be thrown.
     *
     * @param qName a qualified name of the requested instance
     * @return the implementation instance or a proxy to it
     * @throws TargetException
     *          if an error occurs retrieving the instance or the requested component is not an entry
     *          point.
     * @see CompositeContext
     * @see org.apache.tuscany.model.assembly.EntryPoint
     */
    public Object getInstance(QualifiedName qName) throws TargetException;

}