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The intersection of categories would be very nice. Has it been implemented yet? --Gustav 12:12, 5 February 2006 (UTC)Reply[reply]

Using pages as categories[edit]

Current [[Category:X]] mechanism has disadvantages:

  • In many categories it's not evident what items is it designed for. Special description needed, and it's often lost.
  • It's good when categorization is transitive. References used for including into categories are transitive. But they are not transitive to each other, the result is that the structure is deeply broken.
  • Note that almost all good categories have a main page or two.

Idea: why not to link one usual WP page (x) to another one (X) E. g. put in x line (m.b. not single of such)


In article X it's described in first paragaph what Xs are, so user can easily understand is x an X or is not without special page. There is no need for marking Main pages for all #ISA X-marked articles since it automatically is X. There is no need to think if the catname is in single or in plural. Two main articles of a category is an anyhow bad practic (why in en:Category:Energy we see not only en:Energy, but also en:Energy and society (which is really a redirect to Energy industry)?). In such cases we can create a single pages for categorization with chances to develop in real article, if the category is good, otherwise we associate articles to these two separate pages. If X is consequently an XX, we have in X line


- so subcategorization mechanism happens.

Then, for references other than "is-a" (most common is "is part of") we create a subpage like X/Parts, and just put in article X.p a line

 #ISA X/Parts | p

(where p is obviously a sorting key of X.p relatively to X). This subpage can also be categorized independently from X in common way (#ISA Parts of Xish things | X). But in such general cases of relations we even don't have to create this page really. Subpage categories are inherited by ISA reference; if they are not created for current categorizing page, user will be informed about closest co-named categorized subpages in upper ISA levels. #REDIRECT is well for categorizing pages. Possible way of simplifying is referring to subsections of page X, and making a possibility of categorizing subsections independently from whole page:

<!-- in x -->
 x is such an X which is small.
 ==Parts of all good xs==
 #DCAT /Parts <!--alias for subsection categorizing name which should be kept while editing-->
 #DISA Parts of xish things
 All good xs have and x.p1s.

 <!-- in x.p -->
 #ISA x/Parts

For user, near article caption appears letter I, while clicking on it he gets to page like[I 1]


  • Hydrogen in metals
  • Liquid hydrogen
  • Metallic hydrogen


  • Hydrogen atom


  • [+]Hydrogen compounds>>


  • [−]Hydrogen molecula>>
  • Dihydrogen cation


  • [+]Hydrogen isotops>>

Physical propertiesc

  • Electronic polarability#Electronic polarability[I 2]


  • Sabatier reaction


  • [+]Hydrogen economy>>
  • Photohydrogen
  • Timeline of hydrogen technologies

ISA: Chemical element|Gas fuel|Reducing agent|Gas|Nonmetal|Food additive

[show] DISA (8)

Most subpages (ref classes) above are inherited from Chemical element, there is no subpage Physical properties there, so here is link to create it for Hydrogene. This example is not ideally designed, Metallic/Liquid hydrogen and Hydrogen in metals are going into ISA-pages they should never do. There should be created subpage for relation "Agregate state"; "Hydrogen in metals" should go into either "Compounds" or sth like "Systems with metals", but users are people, and such cases will appear (things have different aspects which not always worth disambig but should be ISAed separately).

Such classification mechanism allows to categorize pages in not very more complicated way then current one (in wiki-editor should be a tool which automatically offers from currently referred subpages for categorizing page), and makes search by categories more powerful. Bot can scan pages sublaying given one only by subpages-keys given for first children in path, you also has such ability. I. e., clicking on [+] near Hydrogen compounds will show you Water and many another items, but [+] appearing near Water brings you only Hydrates, not Water museums.

  1. Painted from ru:Категория:Водород
  2. Imitates error - putting #DISA outside of section

Ignatus 18:05, 13 January 2023 (UTC)Reply[reply]