[DFDL-WG] Feature needed: Possible Root element annotation

[Mike Beckerle]

I think IBM DFDL already has this label. I think we need to standardize it
as part of DFDL.

Seems DFDL schemas, to make compilation feasible, and avoid many
unnecessary warnings and spurious weirdness, must have a way of deciding
what top level elements are intended to be Root elements.

Some global element decls might have clearly upward-and-outward relative
path expressions inside them, and such elements are unsuitable for use as
root elements. We don't want to issue diagnostics for these unless the user
expresses intent to use one of them as a root. In that case they have made
a mistake and need a diagnostic.

I believe one could sidestep the issue by only creating elements for things
that could be roots, and use global types or global groups otherwise. But
we have users who really want to use lots of global elements and element
refs for their own reasons (they want the schema to have a certain regular
structure for non-DFDL reasons)

We definitely do see a need for many elements of a schema to be possible
roots. This is particularly important for message-oriented formats where
there is no natural root element that surrounds all the messages because
they are arriving on a non-bounded stream that is effectively open
"forever".


Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology |
www.tresys.com
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