A defacto standard for interchange ("feeds" announcing changes to activities), not for a database (remembering a large set of activities indefinitely). The app

A defacto standard for interchange ("feeds" announcing changes to activities), not for a database (remembering a large set of activities indefinitely). The appropriate schemas are vastly different: a message like iCalendar should be simple and self-contained (leaving cleverness to the applications exchanging it), while a database like the article discusses should be normalized (nontrivial structures and queries aren't a problem).