each X should be have a url based id

[nickevansuk]

There's an over-sensitivity here, as only the Event requires a url based id, and only if the booking specification is also being implemented

[drchristhorpe]

Does this mean that sub-models such as Place, Organisation, Person don't have the requirement for URL based ID?

In our documentation we state - "Information about Events, Places, Organizations and other types of resources should already have been published online to make that information accessible to users. Using existing URLs as identifiers avoids the need to define a new identifier scheme for resources described in opportunity data."