Why Use Categories

Categories allow creators of content to assign a subject to content. This functionality is often refered to as a taxonomy.

For readers of a site, categories have value: readers can drill down to just the section they want to read or subscribe to just one category using their aggregator when the Syndication is enabled on a site. At Urban Vancouver, a section of the site is called Neighbourhoods. Internally, the individual neighbourhoods are categories to which events, blog posts, forum posts and other content can be assigned. People living in the West End of Vancouver may only be interested in content that affects them, so they can bookmark the West End neighbourhood page or subscribe to the RSS feed for the neighbourhood.

Similarly, content producers for other sites can also use the category-level RSS feeds to syndicate content on another site. If a West End community site just wants West End information from Urban Vancouver, they can just syndicate that category's feed.

Some Terminology

Taxonomy refers to the system in Drupal which administrators can determine to organize a site. A taxonomy contains vocabularies, which are groups of categories organized either flatly or hierarchically, and terms are the categories site users will use to tag or label content.

Category Hierarchies

Categories come in three forms: 1) hierarchy-disabled, 2) single hierarchy, and 3) multiple hierarchy. The following image is from the screenshot of the Administer (top menu) » Content management » Categories » add vocabulary tab:

1. Hierarchy-disabled means the category can simply be assigned or unassigned. Some sites will require every piece of content to belong to a category. Urban Vancouver is one such site: every piece of content automatically belongs to the "Vancouver neighbourhood" and then content creators can choose a subcategory--which is an actual neighbouhood of the city--if they choose.
2. Single Parent Hierarchy means the terms added to the category (essentially subcategories) can only have one parent. In the following example, Dairy is the parent of both Milk and Cream, and Soda is the parent of Coke and Pepsi, while Coke is the parent of Cherry Coke and Diet Coke.
• Dairy
• Milk
• Cream
• Soda
• Coke
• Cherry Coke
• Diet Coke
• Pepsi
3. Multiple Parent Hierarchy means that terms added to the category (also essentially subcategories) can have more than on parent, or put another way, can be a subcategory of more than one category. In the following example, Milk appears twice because it has two parents, so when an item is categorized as Milk, it will appear under both Dairy » Milk and Drink » Milk hierarchies.
• Dairy
• Milk
• Cream
• Drink
• Soda
• Milk

Categories in Specific Node Types

As mentioned earlier, specific node types can have categories available just to those node types. For instance, Forums require that a category be set up that recognizes the forum node type. These categories are used to create the structure, or categories, for your forums.