[DFDL-WG] errors and clarifications needed in section 14.2.1 "enclosing group" should be "enclosing sequence" in a few places, "followed in the data" ambiguous.

[Mike Beckerle]

Definitions of Potentially Trailing things mention "enclosing group", but
choices don't qualify. A group in XSD is a sequence or a choice, so if we
mean enclosing sequence, we can't slide by with enclosing group.

We need to to a complete pass through the spec, searching for uses of the
word group. All such should mean "sequence or choice", or should be changed
to one of those otherwise.

My edits for section 14.2.1 are here in colored background:

Potentially trailing element – An array or optional element describes an
occurrence that is said
to be potentially trailing if the element is capable of having a zero
length representation and is
followed in its enclosing sequence definition by only additional
potentially trailing elements or
potentially trailing groups. Intuitively, the array or optional element
occurrence could be last.

Potentially trailing group – A group is said to be potentially trailing if
the group has no framing
and contains only potentially trailing element declarations/references, or
recursively similar
sequence or choice groups, and is followed in its enclosing
sequencedefinition by only additional
potentially trailing elements or potentially trailing groups.

Trailing or Actually Trailing – An element occurrence or group occurrence
in the data is said to
be actually trailing if it is potentially trailing and has zero-length
representation and is not followed
in the data by any other non-zero length element occurrence or group
occurrence limited by the end of the enclosing sequence group.


The phrase "followed in its enclosing group definition..." is meaningless
if the enclosing group is a choice, as choice alternatives don't have an
ordering relationship that corresponds to physical position in the data.

All of these definitions are flawed in the following sense. When we say
last, we mean "last represented" in almost all cases, because another
element following, which has an inputValueCalc doesn't count, nor a
sequence group with no framing, containing only elements with
inputValueCalc or similar sequences, nor an element with complex type
having only that stuff, etc.

So it seems we need the more general concept of "is represented" in the
spec, so that when we say "last" we can be clear.



Trailing or Actually Trailing says "... is not followed in the data by any
other ...". This is unclear because "is not followed in the data" doesn't
express any limit at all. What we mean here is limited by  only up to the
end of the sequence group whose children/separators are under discussion.



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