Ok, Thanks, I'll try to explain my rationale. Orienteering is a sport; an event is a course set on a map, in which people (or in rogaines, teams) may enter different classes (by age range, gender, etc). You can see this in the big model attached to bug 1595405 at <https://sourceforge.net/tracker/index.php?func=detail&aid=1595405&group_id=158881&atid=809608>.
Some events are special, having their own name and identity, and some are un-named, just a part of a series of events. That's what I'm trying to model here. A mathematician might say that a special event is just a single-event series, but that doesn't jibe with actual usage "Are you doing the Four Peaks event this year?", "Fred won A grade in the 2nd event of the Summer Park/Street series," etc.
Now the reason I'm using ORM is that rather than shoot for mathematical models as relational data modelling does, I can capture actual usage. The goal here is to capture the semantics exactly the way the users think, not the way it's convenient to model it, so that when an application UI is built, it *exactly maps* the conceptual model and doesn't need a lot of code written to handle the mapping. In the process, I hope to show that most of the work of building an application can be automated, with the real content moving into the semantic model. A tool can be given a few hints about the navigational model to use, then it can generate a complete working application that just needs visual styling to be complete.
I realize that's a big goal, but I don't believe in setting low goals :-).