For general documentation about the category system, see Help:Category.
On this web site, categories are organized into a set-containment hierarchy: X is a subcategory of Y if every instance of X is an instance of Y. An article may be placed in more than one category, but should only be placed in the lowest applicable categories in the hierarchy.
A QED page should be placed in a category, C, if C is the most specific category for which one of the following criteria is true of the page's subject, as reflected in the title:
- If C is a set, class or type, then the subject is or was an element or instance of C;
- If C is a geographic area, the subject is a geographical entity that is or was located in C;
- If C is an academic discipline or subject area, the subject is a focus of interest therein;
- If C defines a time period, then either the subject is a time period that falls within or overlaps it, or there are events described on the page that fall within it.
The root categories of these four hierarchies are as follows:
QED categories include:
- the CIDOC/CRM classes;
- categories corresponding to the Dublin Core Metadata Element Set as well as to the canonical values of the type element;
- the RDF classes, rooted at rdfs:Resource.
In addition, there is some support for VRA Core 4.0.
For a list of categories currently defined at QED, see:
- Special:Categories — categories with at least one article or media file
- Alphabetical list of all defined categories
Browsing the Category Hierarchy
You can navigate the category hierarchy by visiting any category page or, for more control, by visiting Special:CategoryTree. To expand a category, click on the [+] sign before the name of the category. For further details, see the CategoryTree documentation. Despite the name, the CategoryTree browser does not presuppose a tree-structure.
An interactive graphical representation of the major top-level categories may be found here. It provides a jumping off point for browsing the category hierarchy.
To view all the pages within a category and within its direct and indirect subcategories, see Special:CategoryQuery.
To find pages, images, and files that are each in all of a set of categories, see Special:CategoryQuery. Category Query forms can readily be accessed by clicking on the Index button in the navigation box.
For documentation about a category query language, see Dynamic Page List.
In general, a new category should declare its superclass or superclasses when it is created. If the new category is Small and it is a subcategory of Big, then the category page for Small should include the line: [[Category:Big]].
For further guidance, see also Wordnet.