MediaWiki/docs/Design

Computing: Software: MediaWiki: |Design.doc

Contents
This is a brief overview of the new design. Primary source files/objects:

index.php
Main script. It creates the necessary global objects and parses the URL to determine what to do, which it then generally passes off to somebody else (depending on the action to be taken). All of the functions to which it might delegate generally do their job by sending content to the $wgOut object. After returning, the script flushes that out by calling $wgOut->output. If there are any changes that need to be made to the database that can be deferred until after page display, those happen at the end. Note that the order in the includes is touchy; Language uses some global functions, etc. Likewise with the creation of the global variables. Don't move them around without some forethought.

User
Encapsulates the state of the user viewing/using the site. Can be queried for things like the user's settings, name, etc. Handles the details of getting and saving to the "user" table of the database, and dealing with sessions and cookies. More details in User.doc.

OutputPage
Encapsulates the entire HTML page that will be sent in response to any server request. It is used by calling its functions to add text, headers, etc., in any order, and then calling output to send it all. It could be easily changed to send incrementally if that becomes useful, but I prefer the flexibility. This should also do the output encoding. The system allocates a global one in $wgOut. This class also handles converting wikitext format to HTML.

Title
Represents the title of an article, and does all the work of translating among various forms such as plain text, URL, database key, etc. For convenience, and for historical reasons, it also represents a few features of articles that don't involve their text, such as access rights.

Article
Encapsulates access to the "cur" table of the database. The object represents a Wikipedia article, and maintains state such as text (in Wikitext format), flags, etc.

Skin
Encapsulates a "look and feel" for the wiki. All of the functions that render HTML, and make choices about how to render it, are here, and are called from various other places when needed (most notably, OutputPage::addWikiText). The StandardSkin object is a complete implementation, and is meant to be subclassed with other skins that may override some of its functions. The User object contains a reference to a skin (according to that user's preference), and so rather than having a global skin object we just rely on the global User and get the skin with $wgUser->getSkin.

Language
Represents the language used for incidental text, and also has some character encoding functions and other locale stuff. A global one is allocated in $wgLang.

LinkCache
Keeps information on existence of articles. See MediaWikiDoc:LinkCache.doc

Naming/coding conventions
These are meant to be descriptive, not dictatorial; I won't presume to tell you how to program, I'm just describing the methods I chose to use for myself. If you do choose to follow these guidelines, it will probably be easier for you to collaborate with others on the project, but if you want to contribute without bothering, by all means do so (and don't be surprised if I reformat your code). *I have the code indented with tabs to save file size and so that users can set their tab stops to any depth they like. I use 4-space tab stops, which work well. I also use K&R brace matching style. I know that's a religious issue for some, so if you want to use a style that puts opening braces on the next line, that's OK too, but please don't use a style where closing braces don't align with either the opening brace on its own line or the statement that opened the block--that's confusing as hell. *PHP doesn't have "private" member variables of functions, so I've used the comment "/* private */" in some places to indicate my intent. Don't access things marked that way from outside the class def--use the accessor functions (or make your own if you need them). Yes, even some globals are marked private, because PHP is broken and doesn't allow static class variables. *Member variables are generally "mXxx" to distinguish them. This should make it easier to spot errors of forgetting the required "$this->", which PHP will happily accept by creating a new local variable rather than complaining. *Globals are particularly evil in PHP; it sets a lot of them automatically from cookies, query strings, and such, leading to namespace conflicts; when a variable name is used in a function, it is silently declared as a new local masking the global, so you'll get weird error because you forgot the global declaration; lack of static class member variables means you have to use globals for them, etc. Evil, evil. :I think I've managed to pare down the number of globals we use to a scant few dozen or so, and I've prefixed them all with "wg" so you can spot errors better (odds are, if you see a "wg" variable being used in a function that doesn't declare it global, that's probably an error). :Other conventions: Top-level functions are wfFuncname, names of session variables are wsName, cookies wcName, and form field values wpName ("p" for "POST"). Revision, etc.) to mark file versions. They make merging code between different branches a pain for CVS, and are kind of sketchy for versions after that. (Yes, you can use the '-kk' flag so that merges ignore keywords, but that messes up binary files. See https://www.cvshome.org/docs/manual/cvs-1.11.18/cvs_5.html#SEC64).
 * Be kind to your release manager and don't use CVS keywords (Id,

Edit Log

 * 2005-12-07 post-import cleanup (belated)
 * 2005-06-12 Transcribed from files in MediaWiki 1.4.5