Complex sentence: Since 1999 he has maintained an award-winning Web site, The DiCamillo Companion to British & Irish Country Houses, that seeks to document every English, Scottish, Welsh, and Irish country house, standing or demolished.
Split into simpler sentences: Since 1999 he has maintained a Web database, The DiCamillo Companion to British & Irish Country Houses. The database seeks to document every English, Scottish, Welsh, and Irish country house, standing or demolished.