[DFDL-WG] referencing local element declarations from path expressions between two schema documents

[Mike Beckerle]

I am looking for clarification about how path steps are to be interpreted
with respect to the issue of qualified/unqualified element names, and
default or no-default namespaces.

If there is a precedent we can follow set by other tools which embed paths
into XSD (e.g., schematron?) or even just the selector/paths things in XSD
key/uniqueness constraints then I'd like to understand it.

These are some of the conundrums:

Two Schema Files: A, and B

Schema file A has target namespace AA, and binds the AA namespace to prefix
aa, and the BB namespace to prefix bb
Schema file B has target namespace BB, and the same prefix bindings.

Schema B has an element named b1 which has two local element declarations
inside it named c1 and c2.

Schema A has an element named a1 which contains an element reference to
bb:b1.

a1 has a DFDL annotation (e.g., dfdl:assert) which has a path expression in
it.  this path contains bb:b1/c1

When is the path correct?

1a) when schema B has elementFormDefault='unqualified' (that's the
default), and schema A does NOT have a default namespace. Why? the default
namespace - if it existed for schema A - would implicitly qualify the c1
step of the path, but since c1 is a local element in schema B with element
form unqualified, it does not require (and cannot have) a namespace
specified in path steps for c1.

1b) when schema B has elementFormDefault='qualified', and schema A has
xmlns='BB'. Why? Because in this case the path bb:b1/c1 is equivalent to
bb:b1/bb:c1, and since c1 will have a namespace-qualified name in schema B,
that path will properly describe the path to the c1 element.

1c) Variation: when schema B has no target namespace (which I believe makes
elementFormDefault irrelevant), and schema A has no default namespace.
Because then c1 can't be qualfied as it lives in no namespace, and schema A
has no implied qualifiers.

When is the path incorrect?

2a) when schema A has xmlns="BB". Why? Because the default namespace means
the bb:b1/c1 is equivalent to {BB}b1/{BB}c1, but there is no {BB}/c1 since
c1 is just a local element declaration, and B has elementFormDefault
unqualified.

2b) when schema B has elementFormDefault='qualified', and schema A has no
default namespace. In that case the step c1 needs a namespace qualifier
either by default, or explicitly via a prefix, but it doesn't have one.

So I am interested in opinions on whether the above analysis is correct or
not, and especially in precedent for how this stuff works in other tools.

I have made a big assumption above which is that if xmlns="BB", then any
path step inside something carrying that default binding is interpreted as
qualified by that namespace. I picked this because it seemed reasonable,
and it seems one can always modify one's schema to properly address
something in another schema without having to change that other schema.
I.e., it seems to have good composition properties.

Thanks for any thoughts.


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