* </ul>
     * @throws DuplicateProjectException if any projects are duplicated by id
     */
    // MAVENAPI FIXME: the DAG used is NOT only used to represent the dependency relation,
    // but also for <parent>, <build><plugin>, <reports>. We need multiple DAG's
    // since a DAG can only handle 1 type of relationship properly.
    // Use case:  This is detected as a cycle:

 * This is an inner class, as it must be able to call readRawModel()
 *
 * @since 4.0.0
 */
class DefaultModelTransformerContextBuilder implements ModelTransformerContextBuilder {
    private final Graph dag = new Graph();
    private final DefaultModelBuilder defaultModelBuilder;
    private final DefaultModelTransformerContext context;

    private final Map<String, Set<ModelSource>> mappedSources = new ConcurrentHashMap<>(64);

 * before the {@link Service} reaches the {@linkplain State#RUNNING RUNNING} state. The set of legal
 * transitions form a <a href="http://en.wikipedia.org/wiki/Directed_acyclic_graph">DAG</a>,
 * therefore every method of the listener will be called at most once. N.B. The {@link State#FAILED}
 * and {@link State#TERMINATED} states are terminal states, once a service enters either of these