cdm/src/main/java/thredds/inventory/CollectionManagerAbstract.java
static public CollectionManager open(String collectionName, String collectionSpec, String olderThan, Formatter errlog) throws IOException {
    if (collectionSpec.startsWith(CATALOG))
      return new CollectionManagerCatalog(collectionName, collectionSpec, olderThan, errlog);
    else
      return MFileCollectionManager.open(collectionName, collectionSpec, olderThan, errlog);
  }
static public CollectionManager open(String collectionName, String collectionSpec, String olderThan, Formatter errlog) throws IOException {
    if (collectionSpec.startsWith(CATALOG))
      return new CollectionManagerCatalog(collectionName, collectionSpec, olderThan, errlog);
    else
      return MFileCollectionManager.open(collectionName, collectionSpec, olderThan, errlog);
  }
called from Aggregation, Fmrc, FeatureDatasetFactoryManager