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===Creating subcategories=== ===Creating subcategories===
Create subcategory pages by putting the name of the parent category on the category page that is the subcategory. For example, on a (sub)category page called ''category:Roses'' you put <nowiki>]</nowiki>, Roses becomes a subcategory of Flowers. Child categories (subcategories) are created by putting <nowiki>]</nowiki> '''on the lower-level category pages'''. 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 <nowiki>]</nowiki> '''on the lower-level category pages'''. For example, on a (sub)category page called ''category:Roses'' you put <nowiki>]</nowiki>, Roses becomes a subcategory of Flowers.


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 ''sub''category. 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 ''sub''category.

Revision as of 11:24, 19 November 2004

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This page will serve as a central operating point for the different categorization projects. For a quick introduction to categories, see Misplaced Pages:Category.

When to use categories

Categories should be on major topics that are likely to be useful to someone reading the article.

Article: Michael Jackson
Useful category: Category:Pop singers
Not useful: Category:Musicians whose first name starts with M

Questions to ask to know if a category is the appropriate tool:

  • Is it possible to write a few paragraphs or more on the subject of a 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 a category is probably inappropriate.

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, e.g. Microsoft Office is in Category:Microsoft software, so should not also be in Category:Software. Note: An exception would be an article that defines a category, and so is itself a parent article of subtopics as well as one in a series of like topics - for instance, placing Ohio in both Category:Political divisions of the United States and Category:Ohio. Another example would be cities for which there are categories: New York City belongs in both Category:Cities in New York and in Category:New York City.

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 Category:Stub that are intended to aid the function of Misplaced Pages editing.

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

Categories applied to articles on people

A separate wikipedia page Misplaced Pages:Categorisation of people was created where some finer points of when and how to apply categories to articles regarding people are in the process of being clarified.

Categories form a graph, not a tree

The software feature does not force a strict hierarchy or tree of categories, but allows multiple categorization schemes to co-exist simultaneously. Because each article can appear in more than one category, and each category can appear in more than one parent category, the categories do not form a tree structure, but a more general directed graph. It is even possible to construct loops in the category graph, but this is seldom a good idea.

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.

Guidelines for assignment

If this section stabilizes, it should probably be moved into the User's Guide. -- Beland 08:06, 13 Jun 2004 (UTC)
Maybe with a major rewrite. It is all but useless right now, giving no basic information on How to create categories/subcategories - Marshman 21:57, 5 Jul 2004 (UTC)

How to create categories

Creating a category is as simple as adding a soft link to the appropriate article in the Category: namespace; for instance, to add Felis silvestris catus to the "fluffy creatures" category, you would edit the article and enter ] at the bottom, but before interlanguage links. Although the link will not appear in the article text, a page called Category:Fluffy creatures is automatically created and it will list alphabetically all articles that contain the ] 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.

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 ] on the lower-level category pages. For example, on a (sub)category page called category:Roses you put ], Roses becomes a subcategory of Flowers.

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. The topic may be associated with a geographic area, a historical period, an academic subfield, a certain type of thing (like a food or an ornament), and/or a special interest topic (like Roman Empire or LBGT). 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:Time periods' 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, Queen Elizabeth should not be listed directly under People, but Queens of England might be a good place for her. We know that all Queens of England qualify as Famous Britons and as Royalty, and all of those folks qualify as People. But sometimes there's a good reason to assign an article to two categories, one of which is a direct or indirect subcategory of another. For a well-argued case study, see John Lennon. ('1990' is actually more correct in 'Category:Years', a subcategory of 'Category:Time periods')

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

When a given category gets too crowded, consider making several subcategories. Group similar articles together in a meaningful way that will hopefully be easy for readers to navigate later. Remember that several sub-categorization 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:

  • 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.

Misplaced Pages namespace

Categories relating to the Misplaced Pages namespace should be added only to the talk page of articles. For example, tags suggesting the article is unfinished, or is listed on VfD 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 Misplaced Pages-namespace category.

General naming conventions

  • For a pre-existing category, the article of the same or similar name and (rarely, or) on the same topic should be added to that category. When creating an article one should, only if appropriate (especially horizontally), create a category of the same or similar name on the same topic .
  • Articles should be placed in the most specific categories possible. Categories should be more or equally as broad as the articles they contain; articles should be more or equally specific as the categories they are in.
  • Avoid abbreviations. Example: "World War II equipment", not "WW2 equipment".
  • Don't hard-code the category structure into names. Example: "Monarchs", not "People - Monarchs".
  • Choose category names that are able to stand alone, independent of the way a category is connected to other categories. Example: "Misplaced Pages policy precedents and examples", not "Precedents and examples" (a sub-category of "Misplaced Pages policies and guidelines").
  • Topical category names should be singular. Examples: "Biology", "Law".
  • Standard naming conventions apply; in particular, do not capitalise regular nouns.

Special conventions for lists

  • Category names for lists of items should be plural. Examples: "sports", "writers".
  • In instances where "List of Quuxen" is a simple alphabetical enumeration with no other information on it (unlike List of Twilight Zone episodes, for instance), it could be replaced with "Category:Quuxen".
  • Comprehensive lists, e.g. "List of all municipalities of Quuxen", annotated lists, and selective lists, e.g. "List of Quuxens that were Bazzed", should not be replaced with categories.
  • Names such Category:Lists of Quuexens should be used only for pages with lists, such "List of Quuexens that were sdfdd"
  • See: Category:Lists, Category:Lists that should be categories.

Note that there are a growing number of instances where both the singular category (listing topics relating to) and plural category (listing instances of) exist, for example, Category:Opera and Category:Operas. Be careful to choose the right one when categorizing articles.

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: ] appears as Category:Automotive technologies. Note, however, that when redirecting, the colon must be omitted, as in this example: #REDIRECT ]. Although it is possible to redirect categories in this way, it is not generally recommended because the category containing the redirect will appear as a subcategory of the target category.

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:U.S._Interstate_Highway_system uses this property to sort secondary interstates by their primary. That is, the category link in the article for Interstate 190 is ]. This causes "Interstate 190" to be listed right after "Interstate 90" and right before "Interstate 290" under the heading "9" in the category page.

This feature is very useful:

It can even improve categories lists where every article begins with the same word (example: Category:Mazda).

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-alphabetic character as the first after the pipe. For example, using ] (note the space) would force that article to be displayed before all others. This practice is controversial, however, and thus is discouraged for the time being.

Category extraction

An advantage of categorization is that it allows extraction of large portions of Misplaced Pages. For instance, if years and dates were as below (leftmost items are regular articles, the rest are categories), extracting, say, a timeline for the 21st century would be trivial. 

2004 -> Years in the 21st century -> Years -
                                            \
                                             --> Time periods
                                            /
30 March -----> Days in March ----> Days ---
Please expand this explanation. I see no way from this to "extract a timeline for the 21st century" just a way to create a list of, say, years in the 21st century or days in March. So where is the whoopie in that? - Marshman 17:32, 5 Jun 2004 (UTC)
Where this becomes slightly more interesting is when you have articles on historical events (e.g. Pearl Harbor, John F. Kennedy's Birth, the Great Northeast Blackout, etc.) put in the appropriate time-related category. But the ability to do completely automated extraction depends on how structured the category relationships are. You'd ideally like to be able to specify that the article is about an "event that occurred during" the category or "is a part of" or "is a member of" (say, for geographical or political relationships). So far we can only specify generic parent-child and "is related to" assignments; any other semantics must be inferred. -- Beland 09:32, 13 Jun 2004 (UTC)

Interlanguage links to categories

Interlanguage links work just as they do for regular articles; ] 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.

Current projects

See: Misplaced Pages:Categorization projects (current)

Known category-related bugs

Please report new category-related bugs on bugzilla and list them below.

(Bugs higher than 633 have not been checked)

See also

Browsing categories

Category: