def create_agg_log(db, sessionID):
    """
    Instantiate the Aggregate Data Collection.
    :param db: The database object.
    :param sessionID: Current user's session ID.
    :return: The Aggregate Data Collection object.
    """
    collection_name = 'agg_collection_' + sessionID
    agg_collection = db[collection_name]
    return agg_collection