Just read a great post from long-time code4libber Jonathan Rochkind, [OCFL and “source of truth” — two options][truth].
To give a nutshell summary, it's first useful to be aware of a common web-development pattern, where the 'data' returned by a browser-request comes from an index. That index is an intermediary between the actual source data/file/image, and the webpage a user loads.
Think of the ["Inscriptions of Israel and Palestine" project][IIP] or the ["U.S. Epigraphy" project][USEP]. In both cases, the source-truth of the scholarly data is in xml-files ([example][usep-example]). Knowedgeable trained folk encode data from headstones or other sources into these xml-files.
But when a user performs a search, or loads an inscription-page from the website, the server looks up info from our [solr][solr] indexer.