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text=->%note% This page is still under development.²²(:comment docs based on excerpts form maillist :)²²Categories are already implemented in PmWiki 2, and in most wikis they don't require any special code or markup, they're just a useful convention in Wiki pages. The idea is that every page that is in a given category should have a link to a shared category page.²²There is also a special markup as a shortcut to category-entries: [=[[!category]]=] will create a link to [=Category/category=]²²Since PmWiki has WikiGroups, I'll assume that category links go to the Category group. However, bear in mind that you can use any group or page naming scheme for this -- it's just a convention and doesn't require special programming support. %todo%TODO: special wiki-var for categories²²The key aspects of building a category are:²# On every page that belongs to a category "XYZ", create a link on that page to [@[[Category/XYZ]]@] or [@[[Category.XYZ]]@].²# Then, to see a list of all of the pages that belong to category XYZ, simply do a search to list all pages that have links to the [@Category.XYZ@] page.²->%note%note: all pages that contain the text "Category.XYZ" are displayed. A future version will allow [@(:pagelist linkto=Category.XYZ:)@] or [@(:pagelist backlink=Category.XYZ:)@] (I'm still working on the syntax), which will strictly search for links and not text. %todo%TODO: check implementation and change this docs²²²PmWiki 2 makes this second step incredibly simple, since you can get easily generate a list of all pages with links to [@Category.XYZ@] by doing²² [@(:pagelist Category.XYZ:)@]²²So, that's really all there is to categories. But wait, there's more!²²As John Rankin pointed out in his excellent post, the above convention, combined with the fact that all of the category pages are in a single group, means that we can do much more. If we create a page called [@Category.GroupFooter@], and put the following markup in that page ²² [@(:pagelist Category.{$Name}:)@]²²then every page in the Category group, even empty/non-existent ones, will display a list of pages that are in the category named by the pageFor example, the [@Category.XYZ@] page display will automatically include [@Category.GroupFooter@], and [@{$Name}@] in the [@GroupFooter@] will be replaced by the name of the current page (XYZ) to give us the [@(:pagelist Category.XYZ:)@] directive described above! So, we don't even need to write a bunch of [@(:pagelist Category.<Name>:)@] directives to create the page listings -- just creating a generic one in [@Category.GroupHeader@] or [@Category.GroupFooter@] will do it for all categories we might create.²²->%note%It finds any instances of "Category.XYZ" in the text, and it also finds any page that has an outgoing link to [@Category.XYZ@] (regardless of whether that link was specified as [@[[Category.XYZ]], [[Category/XYZ]], [[Category.X(Y)Z]]@], or even [@[[x y z]]@]).²²->%note%Also, pages such as RecentChanges show up in the category by default and probably should be filtered with [@list=normal@]:²-->%note%[@(:pagelist Category.{$Name} list=normal:)@]²²->%note%(it's not possible to add the non-existent pages as a link in a page, cause this link will automatically turned into an action=edit-link so you can add the link only in the URL-field of the browser)²²So, what do we get? Every page belonging to [@Category.XYZ@] has a link to [@Category.XYZ@], and following that link automatically displays a list of all pages in the [@XYZ@] category.²²But that's not all...!²²The [@Category.*@] pages can themselves be placed into categories! So, to follow John's excellent example, let's suppose we have the following film pages in the categories listed to the right:²² [@Film.SeanOfTheDead [[!Horror]] [[!Comedy]] [[!2003]]@]² [@Film.InMyFathersDen [[!Drama]] [[!2004]]@]² [@Film.TheCorporation [[!Documentary]] [[!2003]]@]²²Now then, we can create [@Category.Horror@], [@Category.Comedy@], [@Category.Drama@], and [@Category.Documentary@], and in each one of those pages we put [@[[!/Genre]]@]. In [@Category.2003@] and [@Category.2004@], we put [@[[!Year]]@].²²So, what happens when we display [@Category.Genre@] ? We see links to "Comedy", "Drama", "Documentary", and "Horror", because they're in the Genre category. When we click on one of those links, we see all of the films listed in one of those categories. Similarly, if we click on [@Category.Year@], we see links to "2003" and "2004", each of which in turn displays the list of films for that year.²²Finally, in [@Category.Genre@] and [@Category.Year@] we can put [@[[!Category]]@], which makes them "top-level" categories reachable from the [@Category.Category@] page. Voila, we now have an instant "hierarchy":²² Category.Category² Category.Genre² Category.Comedy² [@Film.SeanOfTheDead@ Category.Drama² [@Film.InMyFathersDen@ Category.Documentary² [@Film.TheCorporation@ Category.Horror² [@Film.SeanOfTheDead@ Category.Year² Category.2003² [@Film.SeanOfTheDead@ [@Film.TheCorporation@ Category.2004² [@Film.InMyFathersDen@]²²²Note however that this isn't a "strict" hierarchy--i.e., any page or category can appear simultaneously in multiple categories. For example, [@Category.Documentary@] could be a member of both the Genre and top-level category listings.²²Each category page can have content text before the generated list, e.g., to give a generic description of things in the category. (Or it can be empty, which works fine.)²²And all of this works "out of the box" without any modifications to PmWiki 2.0! John goes a step further and proposes that we create a special markup for "Category", so that one can write things like [@[[!Comedy]]@] and [@[[!Genre]]@] instead of the longer [=[[Category/Comedy]]=] and [=[[Category/Genre]]=], but at the moment I'm leaving this as a (one-line!) local customization until it's widely adopted or we have a good standard markup for it. %red% ²%todo%TODO: This is implemented as a test since v2develop25(?)²²->When we choose a good markup, this is all that's needed: (uses [=[[!Comedy]]=] for illustration)²² [=² SDV($CategoryGroup,'Category');² Markup('[[!','<links','/\[\[!([^\|\]]+?)\]\]/' "<span class='category'>[[$CategoryGroup/$1]]</span>");² =]²²Hope this helps. The advantage of a separate category markup is that authors can assign pages to categories independently and explicitly. It lets authors distinguish between a category reference and a reference to a page that happens to be a category page.²²The hard part about using categories is choosing a good vocabulary. Site content managers may wish to follow the Guidelines for the establishment and development of monolingual thesauri (ISO 2788-1986) and the Guidelines for the establishment and development of multilingual thesauri (ISO 5964-1985). Questions to think about include:²* whether a scheme already exists and can be reused²* number of levels in a multilevel scheme (not too shallow, not too deep -- eg 3)²* number of categories per page (not too many, not too few -- eg 3)²* consistent use of singular ([@[[Mercury]] is a [[!planet]]@]) or plural ([@[[Mercury]] is in the [[!planets]] category@])²* disambiguation and use of phrases ([@[[!musical instruments]]@] and [@[[!medical instruments]]@]) or Cookbook/SubpageMarkup ([@[[!Instruments*Musical]]@] and [@[[!Instruments*Medical]]@])²²->%note% (quotes of postings in pmwiki-user-maillist)²²%todo%TODO: add the text of John Rankins post too ?²----²samples (created in groups [@SampleCategory@] and [@SampleFilm@]):²* [[SampleCategory/SampleCategory]] - list of all amples categories used in the sample pages²* [[SampleCategory/GroupFooter]] - see text above²* [[SampleFilm/SeanOfTheDead]] ²* [[SampleFilm/InMyFathersDen]]²* [[SampleFilm/TheCorporation]]²²*%todo%TODO: get back the Sample-Pages from v2-site²*%todo%TODO: document new directive [[!category]] and change samples²----
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