custom post type with taxonomy

1//hook into the init action and call create_book_taxonomies when it fires
2add_action( 'init', 'create_topics_hierarchical_taxonomy', 0 );
3 
4//create a custom taxonomy name it topics for your posts
5 
6function create_topics_hierarchical_taxonomy() {
7 
8// Add new taxonomy, make it hierarchical like categories
9//first do the translations part for GUI
10 
11  $labels = array(
12    'name' => _x( 'Topics', 'taxonomy general name' ),
13    'singular_name' => _x( 'Topic', 'taxonomy singular name' ),
14    'search_items' =>  __( 'Search Topics' ),
15    'all_items' => __( 'All Topics' ),
16    'parent_item' => __( 'Parent Topic' ),
17    'parent_item_colon' => __( 'Parent Topic:' ),
18    'edit_item' => __( 'Edit Topic' ), 
19    'update_item' => __( 'Update Topic' ),
20    'add_new_item' => __( 'Add New Topic' ),
21    'new_item_name' => __( 'New Topic Name' ),
22    'menu_name' => __( 'Topics' ),
23  );    
24 
25// Now register the taxonomy
26 
27  register_taxonomy('topics',array('post'), array(
28    'hierarchical' => true,
29    'labels' => $labels,
30    'show_ui' => true,
31    'show_admin_column' => true,
32    'query_var' => true,
33    'rewrite' => array( 'slug' => 'topic' ),
34  ));
35 
36}