Wordpress: Taxonomy default schema

taxonomy.php

<?php
//hook into the init action and call create_book_taxonomies when it fires
add_action( 'init', 'create_book_taxonomies', 0 );

//create two taxonomies, genres and writers for the post type "book"
function create_book_taxonomies() 
{
	// Add new taxonomy, make it hierarchical (like categories)
	$labels = array(
		'name'                => _x( 'Genres', 'taxonomy general name' ),
		'singular_name'       => _x( 'Genre', 'taxonomy singular name' ),
		'search_items'        => __( 'Search Genres' ),
		'all_items'           => __( 'All Genres' ),
		'parent_item'         => __( 'Parent Genre' ),
		'parent_item_colon'   => __( 'Parent Genre:' ),
		'edit_item'           => __( 'Edit Genre' ), 
		'update_item'         => __( 'Update Genre' ),
		'add_new_item'        => __( 'Add New Genre' ),
		'new_item_name'       => __( 'New Genre Name' ),
		'menu_name'           => __( 'Genre' )
	);

	$args = array(
		'hierarchical'        => true,
		'labels'              => $labels,
		'show_ui'             => true,
		'show_admin_column'   => true,
		'query_var'           => true,
		'rewrite'             => array( 'slug' => 'genre' )
	);
	
	register_taxonomy( 'genre', array( 'book' ), $args );
	
	// Add new taxonomy, NOT hierarchical (like tags)
	$labels = array(
		'name'                         => _x( 'Writers', 'taxonomy general name' ),
		'singular_name'                => _x( 'Writer', 'taxonomy singular name' ),
		'search_items'                 => __( 'Search Writers' ),
		'popular_items'                => __( 'Popular Writers' ),
		'all_items'                    => __( 'All Writers' ),
		'parent_item'                  => null,
		'parent_item_colon'            => null,
		'edit_item'                    => __( 'Edit Writer' ), 
		'update_item'                  => __( 'Update Writer' ),
		'add_new_item'                 => __( 'Add New Writer' ),
		'new_item_name'                => __( 'New Writer Name' ),
		'separate_items_with_commas'   => __( 'Separate writers with commas' ),
		'add_or_remove_items'          => __( 'Add or remove writers' ),
		'choose_from_most_used'        => __( 'Choose from the most used writers' ),
		'not_found'                    => __( 'No writers found.' ),
		'menu_name'                    => __( 'Writers' )
	); 
	
	$args = array(
		'hierarchical'            => false,
		'labels'                  => $labels,
		'show_ui'                 => true,
		'show_admin_column'       => true,
		'update_count_callback'   => '_update_post_term_count',
		'query_var'               => true,
		'rewrite'                 => array( 'slug' => 'writer' )
	);
	
	register_taxonomy( 'writer', 'book', $args );
}