Define how to display one congregation

Store a full history of the congregation's data in the database using several tables like this: congregation table: associates congregation ids with ids of congregation data records; congregation_data table: stores one congregation data record per row, where each record has name, address, phone, etc. columns, plus columns for download source & download date, used for versioning the data. (Note this is not the database schema we have implemented at present.) Display the most recent record's data in black, and where that record is blank, supply the missing data from the most recent record from a DIFFERENT source, displaying it in gray, or if the info is NOT missing in the most recent data from the SAME source (meaning that data has just been deleted), display it with a strikethrough (and maybe in gray.) So, the data needs to be downloaded from the sources on a regular schedule (maybe once per day via a cron job). Decide whether to perform the versioning calculations on-the-fly (while displaying--easy & best if site has low traffic) or immediately after downloading (harder & best if site has high traffic). Later, add widgets allowing a person to get congregation data for a past date. Since congregations can change groups (denominations or presbyteries), version group data as well, and display it this way: list groups at top or bottom of congregation info, gray if not most recent, strikethrough if deleted. In the congregation_data & group tables, add a source hash column (decide how to create the source's hash or UUID--what data makes one source unique? Probably its URL) to prevent downloading data from other Reformed Churches Locator installations in a circular fashion.