To get a list of all categories on the Tclers' Wiki, click on the title "Category Category" at the top of this page.
The top level for the category functionality of this Wiki.
One way to use this Wiki is to click on the title link of any page to get a list of all pages linking back to the current page. The category functionality is built on this mechanism. Links to category pages are intended to be placed on all Wiki pages. Users may then navigate to some category page, click on the "title link" for that page, and get a list of all pages "belonging" to that category.
To create a new category, create a new page representing the category, and place a link to the parent category on the page. There is a suggestion to name all category pages starting with the word, "Category", but this is not required, and many category pages do not do this. One reason is that many pages serve a dual purpose, both as category pages and as the primary content page for some topic.
Category links traditionally are placed at the bottom of a page, ordered from most-specific to least-specific, and using the <<categories>> wiki macro:
<<categories>> Sub Topic | Category
Which will be rendered similar to:
!!!!!! | [Category Sub Topic] | [Category Category] | !!!!!!
If necessary, the <<categories>> macro will prepend the word, "Category" to a page link to resolve it.
A category link on a page should answer the question, "What is this page about?", not the question, "What pages are about the same thing this page is about?". Answers to the latter should either be placed under a "See Also" heading on the page that the similar pages share as a common category, or simply be linked to the same category.
The page, How do Wiki Categories work contains a description of available categories. When adding a new category, please also add a description there.
PYK 2013-09-03:
I am dubious of the value of special category pages because existing pages on each topic already exist, and creating separate pages that serve exclusively to earmark a thing as being a category is messy. For example, the page artificial intelligence exists, and is, by its existence and subject matter, already a category. The page Category AI, though, also exists, for no purpose other than as a node in a hierarchy of separate categories. The actual topic pages would work just as well for the purpose of categorizing things, and become category pages precisely when they are used as an argument to the <<categories>> feature. The advantages are that the category hierarchy can grow more naturally as real topics are added, that an almost redundant set of special "category" pages need not be maintained, and it would be more straight-forward to add additional analytical functionality to the system based on the hierarchy that it could infer from the links and category links an a document.
The meta discussion at Tcl 2008 Conference Talks illustrates the mental gymnastics that a separate explicit set of category pages burdens Wiki users with.
I propose that to achieve the best results for this wiki, editors use the <<categories>> function of the wiki with first-class topic pages instead of category pages, and that we carefully curate pages to provide more substantial, organized, and readable content, even if it means duplicating some of the functionality that categories ostensibly provide. For example, I've started editing the Tcl 2008 Conference Talks to contain a set of links to individual conference presentations, even though such a list could arguably be derived by using the "what links here" functionality of the wiki.
Given enough consensus, the time might even come when editors begin to actively dismantle pages named "Category ...".
EMJ 4 Sep 2013 - a few comments:
PL 2014-03-01: While pages that summarize a topic and provide references to subpages are obviously useful, they are also difficult to maintain as all additions, corrections, and removals have to be manually checked. Hence, we still need the category system, which gives us automatic and accurate references for the much lower maintenance cost of setting category labels on the individual pages correctly. Both systems can be in place and complement each other: they do not disturb or detract from each other in any way. I am in firm opposition to any plan to dismantle the category system.
PYK: The category system is in place, regardless of whether special category pages exist or not, and the current category system already relies on setting category labels on individual pages correctly, and so already incurs this cost. I'm not sure what PL's argument is here. I think he may be missing the point. On another note, to be really functional, the category system needs to provide a way to search for pages based on combinations of categories.
If someone creates a new category and wants to add several pages to it that is a bit more effort. However, since the category system is self-maintaining the total effort is less than creating a list somewhere which has to be manually maintained - if someone who ought to update it actually knows it exists or where it is! That is the point here, along with your reference to "actively dismantling" the Category pages, and I don't think PL has missed it. Anyway, manually maintained lists remind me (dare I mention it to jog some peoples memories?) of Index Pages.
On another note, given the current sqlite-powered enhanced search , combined queries and all sorts of other complex searches are now quite easy.
Obviously, I also am in firm opposition to any suggestion that the category system might be dismantled.
PYK 2014-03-01: I believe EMJ has somehow also missed the point here. The argument is not to replace the category system with manually-maintained lists, but to use, e.g., object orientation as a category instead of using category Object Orientation. Also, I would love to see an example of finding pages based on some combination of categories, as I've not-yet figured out how to do that.
PL: It seems that it comes very easily to you to dismiss criticism or opposition with the verdict that the people who don't agree with you are "missing the point". I admit that there are many cases where I personally don't see the point of what you're doing, like for instance your odd habit of rewriting perfectly good text by breaking lines at some arbitrary length, making it a major chore to maintain the text without removing those linebreaks again. However, when you talk about it being "messy" to have pages like Category AI side-by-side with pages like artificial intelligence, then I'm afraid that the missing of the point is on your side entirely (and your response to what I wrote also hints that you haven't really thought this issue through). It may be necessary to repeat this: this wiki is not your personal domain, and you are not welcome to rebuild it to suit your preferences. If you want to suggest a change in how pages are organized (as opposed to correcting texts, fixing links, improving the layout of pages, etc) it's absolutely essential that you bring this suggestion up for general discussion before you go ahead and make this change.
EMJ: What he said! And even if I had misinterpreted your viewpoint on categories, I still object to the new version. See firstly my second comment from September 2013. In addition, if you don't label it a category how will anyone know it is a category, unless they happen to see it referred to at the bottom of some other page?.
PYK 2014-03-1: That's precisely how you would know, and that's the only time you really care. Using regular pages as category pages would not affect the current operation of the wiki category system at all. The only difference is that there would be less confusion about where to put information on, e.g., Artifical Intelligence, because there would only be one page on that subject instead of two. Regarding EMJ's 2013-09 response, yes, categories are better used as a set of disjoint tags rather than as a hierarchy, which I see as one more reason that explicit category pages need not exist. However, I do see the point about explicit category pages that have no content being useful as the unencumbered ideal handle for the subject. Maybe that alone is enough to keep them around.