I encourage anybody who's spent any time developing for MediaWiki to
go and read
https://www.mediawiki.org/wiki/MediaWiki_architecture_document/text
-- it's thorough! There are some FIXMEs in there where Guillaume
requests more details about performance, caching, and skins, so if you
can add some more info on the talk page this week, that would be
great.
And it would be wonderful if someone with some Inkscape ability could
put together a diagram or two that would help readers understand the
architecture of MediaWiki. (Trevor?) Guillaume mentioned to me that
he's looked at all the existing diagrams and none are quite right.
Sumana Harihareswara
Volunteer Development Coordinator
Wikimedia Foundation