Categories are similar in concept to tags, but are designed with the administrator in mind, not the end user. Hierarchies of categories can be created, and categories can be grouped together in Vocabularies. Where tags represent an ad hoc method for users to group content together, categories exist to allow administrators to organize content in a more official, hierarchical structure. As has been said in Chapter 3, think of tags like the index to a book and categories like the table of contents. Both serve the same purpose: to help the user find the information he or she seeks.
Adding vocabularies and categories is similar to adding tags. Once you've selected the community or organization you want to work on, select Categories from the content section of the control panel, and you will be presented with the categories administration screen.
Illustration 88: Categories administrationClicking on a vocabulary on the left will display any categories that have been created under that vocabulary. You can create new vocabularies simply by clicking Add Vocabulary and providing a name for it. You can create categories in a similar fashion by choosing a vocabulary on the left, and then selecting Add Category. Like tags, you can also provide properties for categories.
Once you have created some vocabularies and categories, you can take advantage of the full capabilities of categories by creating a nested hierarchy of categories. To nest categories, select what you want to be the parent category, then drag any category that you want to become a child category onto it. You will see a plus sign appear next to the name of the category you are dragging if you can add it to the selected parent category; if you see a red x that means that you cannot add that category as a subcategory of parent category that you have selected.
Illustration 89: Adding a subcategory
Once you have created a hierarchy of categories, your content creators will have them available to apply to content that they create. Under the Categorization section of the content creation screen, click the button labeled Select under the Categories heading. A dialog will appear with your vocabularies and categories. Select any relevant categories by checking the box next to them, and they will be applied to the content.