A short background on categories

Categories are a built-in content relation in OpenCms and allow files in the VFS to be assigned one or more topics/keywords/whatever. They can often be used as a replacement feature for siblings which are mostly misunderstood by users without a technical background. For example consider the typical example of a news site. You have a folder structure for your articles which could be the following way:

/articles/2008/12-24-merry-christmas.html
/articles/2009/09-01-new-site.html
/articles/2009/10-02-a-great-article.html

You now want to categorize the articles into topics so you would create another folder structure:

/topic/must-read
/topic/technical

The sibling-way would be to create a sibling (put simply: an automatically updating copy) of the articles in the desired topic folder. While this is a working solution it’s counterintuitive to most users. OpenCms 7 introduced the long awaited Content Relation Engine (CRE) including a default relation called categories. Similar to the sibling solution a category is effectively a folder but instead of creating it anywhere in the filesystem it’s created in the root site (“/”) under /system/categories/. Users can now assign categories to VFS files using the context-menu entry Relations -> Assign Categories. This is a much easier approach although it has one caveat: Categories are globally defined in the /system/ folder and can therefore only be created by users with access to the root site and can not be specified on a per site or even per folder basis. This can cause problems in multisite environments.

Decentralization to the rescue

With OpenCms 7.5 this limitation is finally gone. You can now define categories on a per-site and even per-folder basis. Simply create a folder named _categories in the folder where you want the categories to be available. Then create new folders inside this folder to define categories. The categories are available in the parent folder of the _categories-folder and all subfolders. They also cascade down. Example:

/de/_categories/
/de/_categories/hot-topic
/de/_categories/support
/de/news/_categories/
/de/news/_categories/marketing
/de/news/_categories/development

Inside the /de/ folder the categories hot-topic and support are available. Inside /de/news/ the categories hot-topic, support, marketing and development are available.

This feature should easily help you to get your content structured more nicely. Speaking from experience it is crucial to create an evolveable content structure upfront so your editors as well as visitors and search engines get the most out of your site.

See also:

• Presentation from Michael Moossen about the CRE at OpenCms Days 2008
• A guide to good URI design