Markup spec/DTD

Introduction

This is a draft of Wikipedia DTD, an interchangeable XML representation of the content of wikipedia articles. It contains elements for the content of an article (Wikitext DTD). This is also a contribution to get a formal wikitext standard that is still lacking. When there is such a standard multiple suites of software (some based on mediawiki, some not) could support it, and each Wikipedia could choose between them, while supporting the same portable open content.

Important notes

Wikipedia DTD is an interchange format. It is not to be meant to write articles in it nor to replace a database!

Up to now I (Jakob Voss) am the only author of the Wikipedia DTD but this is meant to be collaborative work in progress—feel free to contribute. Though you should at least know XML basics. Please add comments on Talk:Wikipedia DTD. I am also working on simple WikipediaDTD-to-HTML and WikipediaDTD-to-Wikitax scripts that will be made public soon. The most important thing to use Wikipedia DTD in real life is a Wikitax-2-XML parser. The possibility to mix wiki syntax with invalid HTML is quite complicated.

On Compatibility: Up to now there are wikipedia-articles containing data that will not fit into wikiarticle.dtd because they contain broken or ugly HTML. Some elements that are still allowed in wikitex should have to be removed (for instance, HTML-coded headings and horizontal lines or the font-element). This is a topic to discuss.

Still missing parts: table, dl, pre, div, ruby, font, var. And many attributes

Advantages

You could also use an XML representation to

produce valid XHTML
produce printable output (for instance PDF with FO), see also de:Automatisierte PDF-Erstellung
export Wikitax to other formats (for instance w:DocBook)
export other formats to Wikitax (for instance OpenOffice files)
perform automatic analysis on structure and layout of articles
exploit better XML-based tools to define and extend wikitax
integrate specialized DTDs for "who" (m:person_DTD), "when and where" (m:spacetime_DTD) easily, as long as the tag spaces are distinct

Wikipedia articles

Root element

Up to now the Wikipedia DTD is only meant to single articles so the root element is article. There is a metadata section containing the title and other stuff and the article content itself that may be text or a redirect.

<!ELEMENT article (meta, (wikitax | text | redirect))>

Linking model

Links (to other articles) are one of the most important things in Wikipedia. In most cases they simply consist of an article name, but there may also be namespaces. In Wikipedia there are 9 namespaces: default (none), talk, user, user-talk, wikipedia, wikipedia-talk, image, image-talk and special. The names of namespaces may differ in different languages but the namespaces remain the same. For instance there is no namespace Diskussion, it is only the german name for the talk namespace. Local names are not part of the Wikipedia DTD.

I prefer separating the talk-property of a namespace.

<!ENTITY % possible-namespaces "(special | user | wikipedia | image)">

<!ENTITY % local-link-model " 
	talk (talk) #IMPLIED
	namespace %possible-namespaces; #IMPLIED
	article CDATA #REQUIRED
">

The attributes of the local-link-model parameter entity form a full local link destination.

Metadata elements

The metadata section contains information about title, status, version history and interwiki links. Only the title is obligatory. There may be added elements for copyright information, category-links and other this-is-much-more-dublin-core-than-article-content-stuff.

<!ELEMENT meta (title, status?, interwiki*, history?)>

Title

The title of an article does not change - so it is not part of the article history. Since a title may contain namespaces it is the easiest to specify the full title as a link to the article itself. The interwiki-attribute may specify the wiki the article comes from (normally a language).

<!ELEMENT title EMPTY>
<!ATTLIST title	
	interwiki NMTOKEN #IMPLIED
	%local-link-model;
>

Interwiki links

There are several reasons why interwiki links belong into the metadata section. Interwikilinks are relations of an article (maybe there will be other relation types in the future) in spite of normal links in the article content that may mean several things. Concurrently there may be links to other wikipedias inside the article content. Do not mix this. Interwiki links use the same #Linking model as other links but they must specify a known language.

<!ELEMENT interwiki EMPTY>
<!ATTLIST interwiki	
	language NMTOKEN #REQUIRED
	%local-link-model;
>

Article Status

The status element contains status information like whether the article is protected, whether a table of contents should be shown etc. Since the status may change due edits it´s also part of the article history.

<!ELEMENT status EMPTY>
<!ATTLIST status
	protected (protected) #IMPLIED
	counter CDATA #IMPLIED
	notoc (notoc) #IMPLIED
>

Note: In the actual database the counter (number of times a page has been viewed) is only saved for the current version. This should be changed in the future to get more usage information (for instance to see how often a page has been viewed since the last edit or to detect edit-wars automatically).

Version history

The version history simply contains a number of edits.

<!ELEMENT history (edit)+>

Each edit contains the edit information (user, timestamp...) and the current status, interwiki-links and content of an article after the edit. The article content is optional—if it is not provided there is just no change or it is just not included because we are not interested.

<!ELEMENT edit (status?, interwiki*, (text | redirect)?)>
<!ATTLIST edit
	user CDATA #REQUIRED
	comment CDATA #IMPLIED
	timestamp CDATA #IMPLIED
	minor (minor) #IMPLIED
>

An example of a timestamp is

2002-02-25T15:43:11Z

This is YYYY-MM-DDThh:mm:ssZ, where YYYY is year, MM is month, DD is date, hh is (24-hour) hour, mm is minute, ss is second, and T is a separator, and Z (here) is Zulu, a letter in the international code of signals. There are 24 major time-zones in the world, represented by the letters A(lpha) to Z(ulu). The letters I(ndia) and O(scar) are omitted to avoid confusion with the numbers 1 and 0. Zulu hour corresponds to Greenwich Mean Time, GMT, also called Universal Time Corrected, UTC, which is the standard time used in navigation and on the Internet.

Redirects

Either an article contains a redirect or text. Redirects are links to articles in the same wiki.

<!ELEMENT redirect EMPTY>
<!ATTLIST redirect	
	%local-link-model;
>

Wikitax

Since there is no Wikitax2XML-parser yet the article content could also be transfered in Wikitax. Since Wikitax depends on the Wikimedia software and might change a version information should be provided.

<!ELEMENT wikitax (#PCDATA)>
<!ATTLIST wikitax 
  version CDATA #REQUIRED
>

Wikitext

An XML representation of article content is the core of Wikipedia DTD. You can also use this part alone.

<!ENTITY % wikitext-block "ul | ol | center | blockquote | pbr | hr | h1 | h2 | h3 | h4 | h5 | h6">
<!ENTITY % wikitext-inline-format "b | i | sub | sup | big | small | tt | u | br | nowiki">
<!ENTITY % wikitext-inline-special "math | wikivar | link | reference | url">

<!ENTITY % wikitext-inline "%wikitext-inline-format; | %wikitext-inline-special;">

There are missing some not yet defined elements in the parameter entities.

<!ELEMENT text (#PCDATA | %wikitext-block; | %wikitext-inline;)*>

Block elements

Headings, horizontal line

In contrast to HTML there are no attributes.

<!ELEMENT h1 (#PCDATA | %wikitext-inline;)*>
<!ELEMENT h2 (#PCDATA | %wikitext-inline;)*>
<!ELEMENT h3 (#PCDATA | %wikitext-inline;)*>
<!ELEMENT h4 (#PCDATA | %wikitext-inline;)*>
<!ELEMENT h5 (#PCDATA | %wikitext-inline;)*>
<!ELEMENT h6 (#PCDATA | %wikitext-inline;)*>

<!ELEMENT hr EMPTY>

Indented lines

<!ELEMENT indent (#PCDATA | %wikitext-inline;)*>
<!ATTLIST indent
  depth CDATA '1'
>

Lists

To avoid #PCDATA and sublist mixing we define oli=li+ol and uli=li+ul

<!ELEMENT ol (li | ol | uli)+>
<!ELEMENT ul (li | oli | uli)+>
<!ELEMENT oli (li | ol | uli)+>
<!ELEMENT uli (li | oli | uli)+>

<!ELEMENT li (#PCDATA | %wikitext-inline;)*>

TODO:

attributes: "type", "start", "value", "compact",
definition lists

Tables

TODO

elements: table, tr, td, th
attributes: "summary", "width", "border", "frame", "rules", cellspacing", "cellpadding", "valign", "char", charoff", "colgroup", "col", "span", "abbr", "axis", headers", "scope", "rowspan", "colspan"

center, blockquote

<!ELEMENT center (#PCDATA | %wikitext-inline;)*>

<!ELEMENT blockquote (#PCDATA | %wikitext-inline;)*>
<!ATTLIST blockquote
	cite CDATA #IMPLIED
>

pre, div

TODO (what is allowed inside? - div as block and inline?)

Paragraph breaks

Wikitax provides a way to separate paragraphs: just add an empty line. In Wikitext DTD this is represented by the tag ‎<pbr /> (paragraph break). The possibility to create paragraphs with ‎<p> should be abolished because it leads to broken XML and we should reduce the number of allowed HTML-tags.

<!ELEMENT pbr EMPTY>

Inline elements

Wikitext special elements

TODO: nowiki, media

nowiki parts

<!ELEMENT nowiki (#PCDATA)>

Links

See #Linking_model for details.

<!ELEMENT link (#PCDATA | %wikitext-inline-format;)*>
<!ATTLIST link
	interwiki NMTOKEN #IMPLIED
	%local-link-model;
>

Math

The image attribute may provide an image representation

<!ELEMENT math (#PCDATA)>
<!ATTLIST math 
  image ENTITY #IMPLIED
>

URL

<!ELEMENT url (#PCDATA | %wikitext-inline-format;)*>
<!ATTLIST url
  href CDATA #REQUIRED
>

Reference

<!ELEMENT reference EMPTY>
<!ATTLIST reference
   system (email | RFC | ISBN) #REQUIRED
   value CDATA #IMPLIED
>

Images and other media files

<!ELEMENT media EMPTY>
<!ATTLIST media
   name CDATA #REQUIRED
   data ENTITY #IMPLIED
>

bold/italic

strong and em will never be used in the right way so use b and i instead. There are no attributes allowed.

<!ELEMENT b (#PCDATA | i | big | small | sub | sup | tt | u | br | %wikitext-inline-special;)*>
<!ELEMENT i (#PCDATA | b | big | small | sub | sup | tt | u | br | %wikitext-inline-special;)*>

Several HTML tags

Several HTML-tags are also allowed in Wikitext DTD, but most of them are simplified in some way (for instance no or less attributes). These tags are not HTML - they are like the same HTML-tags, not equal!

<!ELEMENT tt (#PCDATA | b | i | big | small | sub | sup | u | br | %wikitext-inline-special;)*>
<!ELEMENT u (#PCDATA | b | i | big | small | sub | sup | tt | br | %wikitext-inline-special;)*>
<!ELEMENT sub (#PCDATA | %wikitext-inline;)*>
<!ELEMENT sup (#PCDATA | %wikitext-inline;)*>
<!ELEMENT big (#PCDATA | %wikitext-inline;)*>
<!ELEMENT small (#PCDATA | %wikitext-inline;)*>
<!ELEMENT br EMPTY>

TODO: ruby-tags

Variables

Some dynamic variables can be used in Wikitax as {{VARNAME}}.

<!ELEMENT wikivar EMPTY>
<!ATTLIST wikivar
  name (CURRENTMONTH | CURRENTMONTHNAME | CURRENTDAY | CURRENTDAYNAME |
        CURRENTYEAR | CURRENTTIME | NUMBEROFARTICLES)
  #REQUIRED
>

Open questions

div (yes), font (no), var (why).

Why use a <div/> container? Use something like <para/> instead. Div's are usually used for content formatting, not structuring (at least I believe they should not be used for this). One container for paragraphs is absolutely sufficient.

What to do with/where to allow universal HTML attributes (id, class, name, style)?

You should never allow id, class or style - all are used to refer to a CSS stylesheet. The Wikipedia DTD must not care about content formatting! The XML should be treated as a data container only. If you want special formattings, use an XSL stylesheet.

remove id and name, allow class and style at some elements
Should we create a custom DTD? Would Docbook or Simplified Docbook work? If so, would it be better to use a standard format rather than make up our own?

If Docbook would work, it would definitely be a wiser choice than inventing the wheel twice. There are many utilities and stylesheets to work with Docbook content. If Docbook alone is not enough, try to use it as a base and only define the extensions of the DTD.

Or, create a DTD with an ontology optimized for mediawiki, but with a mapping to (simplified) docbook. Have it both ways.