Wraf: Versioning

Versioning will be implemented as views.

We want to get statements that are 1) correct and 2) current. A statement (or all statements in a model) can be withdrawn.

A statement can be withdrawn because it has allways been false. See truth.

The second type of versioning says that some statement is true during a specific time period. So let us specify that we want to know the properties of a thing, as it was in 1999. $thing->arc( valid_during => $date_range )->list. All this is dependent on that we decide on how to describe dates, and more. The valid_during talks about the arc and not the object. The valid_during can be dynamicly infered from other properties; for example from the model.

Not implemented