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Blue check.gif This page is considered a guideline on DCCWiki. It illustrates standards of conduct, which many editors agree with in principle. However, it is not policy. Feel free to update the page as needed, but please use the discussion page to propose any major changes.

This article provides guidelines on creating and organizing categories.

For a quick introduction to categories, see DCCWiki:Category. This page for everything that you ever wanted to about categorization.

When to use categories

Every page in the article namespace should belong to at least one category. Categories should be on major topics that are likely to be useful to someone reading the article.

Article: Digitrax DT400R Tips
Useful category: Category:Throttles
Not useful: Category:Things that make me ill

Questions to ask to know whether it is appropriate to add an article to a category:

  • If the category does not already exist, is it possible to write a few paragraphs or more on the subject of the category, explaining it?
  • If you go to the article from the category, will it be obvious why it's there? Is the category subject prominently discussed in the article?

If the answer to either of these questions is no, then the category is probably inappropriate. Note that it is always appropriate to add articles to categories that fit into well established taxonomies. For example, every article about a throttles is categorized in Category:Throttles category, which is in turn categorized in Category:DCC.

An article will often be in several categories. Restraint should be used, however — categories become less effective the more there are on a given article.

An article should not be in both a category and its subcategory, for example LocoNet is in Category:Throttle network, so should not also be in Category:DCC.

Categories appear without annotations, so be careful of NPOV when creating or filling categories. Unless it is self-evident and uncontroversial that something belongs in a category, it should not be put into a category.

Exceptions to the above rules are categories such as Stub categories which are intended to aid the function of DCCWiki editing.

For alternative methods of grouping articles, and the circumstances in which they should be used, see DCCWiki:Categories, lists, and series boxes.

For articles without any stable category, {{catneeded}} tag can be used to bring attention (although Special:Uncategorizedpages exists).

Categories vs. Lists vs. Info boxes

See, DCCWiki:Categories, lists, and series boxes.

Categories applied to articles on people

A separate DCCWiki page DCCWiki:Categorization of people was created to help you in designing, applying and checking categories that are used for articles on people.

Categories do not form a tree

Each DCCWiki article can appear in more than one category, and each category can appear in more than one parent category. Multiple categorization schemes co-exist simultaneously. In other words, categories do not form a strict hierarchy or tree structure, but a more general directed acyclic graph (or close to it, see below).

Nevertheless, parts of the category graph will be tree-like, and it may be convenient to think of parts of the category graph as being like multiple overlapping trees.

Cycles should usually be avoided

Although the DCCWiki software does not prevent cycles (loops), these should usually be avoided.

Guidelines for assignment of categories

As the DCCWiki website grows, more categories are needed. Please follow naming standards creating new categories, or assigning articles (pages) to categories.

How to create/assign categories

Creating a category is as simple as adding a soft link to the appropriate article in the Category: namespace; for instance, to add Digitrax PM42 to the "power management" category, you would edit the article and enter [[Category:Power management]] at the bottom. Although the link will not appear in the article text, a page called Category:Power management will automatically list alphabetically all articles that contain the [[Category:Power management]] link. The appeal of categories is that unlike lists, they update themselves automatically, and that one can use them to quickly find related articles. However, categories are not a substitute for lists, and you will find that many articles belong to both lists and categories. You may see some inconsistencies when first creating the category: it may alternate between appearing empty and appearing with your first additions. It will probably correct itself in a few minutes.

Note that, although "uncreated" categories will correctly list articles that have been assigned to them, the category page itself does not exist until it is manually created. The easiest way to create the category page is to follow the edit link from an article and add a parent category and a category description as explained below.

Creating subcategories

Create subcategory pages by putting the name of the parent category on a category page that you would like to be the subcategory. Child categories (subcategories) are created by putting [[category:parent_category_name]] on the lower-level category pages. For example, on a subcategory page called category:Throttles you put [[category:DCC]] in at the bottom of the page. Throttles becomes a subcategory of DCC.

When adding an article to a category, or creating categories, one should be careful to use the correct categories and subcategories. Horizontal categorization, directly below, refers to placing an article in the correct category while vertical categorization refers to placing an article in the correct subcategory.

When assigning an article into categories, try to be thorough in a "horizontal" sense. You might need to poke around the category hierarchy a bit to find the right place. Try searching for articles similar to the article you are categorizing to get ideas or to find the most appropriate place. (For instance, '1990' is more correctly in 'Category:Years' rather than 'Category:Places'.)

In the "vertical" dimension, you should probably be more frugal. A good general rule is that articles should be placed in the most specific categories they reasonably fit in. For example, Digitrax should be should not be listed under DCC, but under DCC Manufaturers.

Whatever categories you add, make sure they do not implicitly violate the neutral point of view policy. If the nature of something is in dispute (like whether or not it's fictional or scientific or whatever), you may want to avoid labelling it or mark the categorization as disputed. Most categorizations are pretty straightforward, though.

Making groups of subcategories

Categories can only list 200 entries at a time. When there are more than 200 entries, only the first 200 will be displayed. To make it easy to navigate, add a TOC (table of contents). TOCs are added by typing:

{{CategoryTOC}} - which adds a complete TOC (Top, 0 - 9, A-Z)
{{CatAZ}} - which adds a TOC without numbers. This is for categories with members that only start with letters.

When a given category gets crowded, also consider making several subcategories. Group similar articles together in a meaningful and useful way that will make it easy for readers to navigate later. Remember that several subcategorization schemes can coexist (for example, if Category:Software gets too big, you don't have to choose between subdividing it by function or subdividing it by platform, you can simultaneously subdivide it in both ways).

A set of related categories often forms a hierarchy or a nexus. This can take several different forms, all of which are welcome and encouraged:

Revise for DCC topics related topics.

  • Hybrid forms. For example, Category:Art is both part of the taxonomy of Category:Academia and a cross-reference point for lots of things that have little in common except that they have something to do with art.

Category membership and creation

When writing the description for a category, give it a parent category. In fact, you should try to give it at least two parent categories. For example, Category:British writers should be in both Category:Writers by nationality and Category:British people. A few categories do only merely subdivide their parent category, but unless the parent category has many potential articles under it, or many potential subdivisions, if you can't think of a second parent category, it might be a better idea to fold your smaller category into the parent.

DCCWiki namespace

Categories relating to the DCCWiki namespace should be added only to the talk page of articles. For example, tags suggesting the article is needs work, would be placed on the talk page as they are relevant to editors, not an aid to browsing in the way ordinary categories are. Please use {{wpcat}} on the Category description page to show that it is a DCCWiki-namespace category.

User namespace

Categories relating to the User namespace should be added only to DCCWiki-specific categories. Users should not add their user pages to article namespace categories such as Category:People or other subcategories, Category:Biologists etc, which are reserved for pages in the article namespace. However, it is appropriate to add a user page to DCCWiki-specific categories such as Category:DCCWikipedians or other similar subcategories such as Category:DCCWikipedian musicians.

If you copy an article to your user namespace (for example, as a temporary draft or in response to an edit war) you should decategorize it.

Image namespace

See categorizing images.

Category naming

Categories follow the same general naming conventions as articles, for example do not capitalise regular nouns. For specific conventions related to categories, see DCCWiki:Naming conventions (categories).

Categories requirements and usage

User browsing

Categories (along with other features, like cross-references) should help users find the information they are looking for as quickly as possible, even if they don't know that it exists or what it's called.

Links to categories

You can create a link to a category page without adding the page to that category by using a colon before the word Category. Example: [[:Category:Automotive technologies]] appears as Category:Automotive technologies.

Redirected categories

Although it is possible to attempt to redirect categories by adding a line such as #REDIRECT [[:Category:Automotive technologies]] to a category, it is not generally recommended because of limitations in the mediawiki software. Categories "redirected" in this way do not prevent the addition of articles to the redirected category. Articles added to the "redirected" category do not show up as in the target category. Until these issues are addressed (in future versions of the software), #REDIRECT should not be added to category pages.

Category sorting

Contrary to some expectations, text after a pipe ("|") in a category link is not used in place of the category text. Rather, this text is used as the sort key on the category page itself. However, again contrary to expectations, that sort text is not displayed.

For example, the Category:Three-digit Interstate Highways uses this property to sort secondary interstates by their primary. That is, the category link in the article for Interstate 190 (Illinois) is [[Category:Three-digit Interstate Highways|90-1 Illinois]]. This causes "Interstate 190 (Illinois)" to be listed right after "Interstate 189" and right before "Interstate 290 (Massachusetts)" under the heading "9" in the category page.

This feature is very useful for categories in which:

Using this method to sort category entries is sometimes informally referred to as the pipe trick. However, this use of the pipe character is very different from the original Wikimedia pipe trick which allows one to easily hide parenthetical disambiguation in links.

It is possible to force an article or subcategory to the top of the list by using a non-alphanumeric character as the first after the pipe. For example, using [[Category:Ford| Ford Motor Company]] (note the space) or [[Category:Ford|*Ford Motor Company]] would force that article to be displayed before all the others.

Year categories

In categories which are years, such as Category:2004, special sorting guidelines apply:

  • Entries should generally be sorted by topic, so the article 2004 in film, for example, would contain the category reference [[Category:2004|Film]] while 2004 Canadian budget would contain the reference [[Category:2004|Canadian budget]]; List of religious leaders in 2004 would contain [[Category:2004|Religious leaders]].
  • The article about the year itself, 2004, should be sorted first among all articles by using [[Category:2004|*]].
  • Articles for individual months, such as October 2004, should be sorted chronologically in the first section on the category page, in this case using [[Category:2004|*2004-10]].

Interlanguage links to categories

Interlanguage links work just as they do for regular articles; [[de:Kategorie:Mathematik]] in Category:Mathematics connects to the German counterpart. This can be a useful way to compare coverage, or to look for articles in need of interlanguage links. Note that the different languages may have adopted different standards and practices for categorization, so a given category might not exist in other languages.


  • Pearle can be used to automatically move articles from one category to another, get dumps of the category trees, and accomplish some other useful category-related tasks.

Current projects

See: DCCWiki:Categorization projects (current)

See also

Browsing categories