[dfdl-wg] Annotation complexity
Myers, James D
jim.myers at pnl.gov
Fri Nov 19 15:12:52 CST 2004
I think I get the issue, but not necessarily the proposed solution. I
can have an element with a complex type that contains other elements
with complex types and I might want params such as littleendian to
follow that hierarchy, independent of the type derivation hierarchy. Are
you saying that inheritance should never flow down the 'contains'
hierarchy?
Jim
PS. After two days of this in December, I may need help in getting
myself to the airport ... ;-)
-----Original Message-----
From: owner-dfdl-wg at ggf.org [mailto:owner-dfdl-wg at ggf.org] On Behalf Of
Suman Kalia
Sent: Friday, November 19, 2004 3:47 PM
To: dfdl-wg at gridforum.org
Subject: Fw: [dfdl-wg] Annotation complexity
You are beginning to see the complexities of overrides in this
very simple example. Consider complex type hierarchy which is four/five
levels deep and then determine which override is applicable and where in
the tree. I briefly mentioned in the call on Wednesday, that we should
carefully determine which annotations are applicable for which
constructs of XML schema and try to avoid the override mechanism.
Annotations that exist on the element belong only to the
element; there is no inheritance or override issue here. Annotations
that exist on structural constructs (group/complex types etc) truly
belong to the structure only ( such as data element separators,
delimiter which cannot be associated with elements because elements
could be reused via element Ref in other structures where they could
have different delimiter in that structure etc). Once we have
separated the types and elements; then annotations defined on derived
types can follow the well established rules of inheritance ie inherit
annotation from parent unless explicitly overridden etc..
Then comes the issue of defaults - where to locate and apply.
Possible options are a) top level type ( which for example could be
type corresponding to 01 level COBOL structure) b) A separate
structure available at tooling and runtime which contains the defaults.
We used the latter in our implementation.
Suman Kalia
IBM Toronto Lab
WebSphere Business Integration Application Connectivity Tools
Tel : 905-413-3923 T/L 969-3923
Fax : 905-413-4850
Internet ID : kalia at ca.ibm.com
----- Forwarded by Suman Kalia/Toronto/IBM on 11/19/2004 03:04
PM -----
"Myers, James D" <jim.myers at pnl.gov>
Sent by: owner-dfdl-wg at ggf.org
11/19/2004 02:25 PM
To
dfdl-wg at gridforum.org
cc
Subject
RE: [dfdl-wg] Annotation complexity
I guess I'm not sure how restricting annotations to elements
solves
things. I think I can recreate the problems in Martin's examples
without
putting annotations on types:
The issue of it being hard to understand that triple overrides
the
dfdlfromstrings param would seem to be the same whether the
triple type
has an annotation or if some subelements within it get
annotations
(either first second and third, or consider a triple type that
specifies
an annotated element containing those three). In all these
cases, it is
clear that you have to walk down the logical hierarchy which is
broken
into parts in the dfdl/xsd file and keep a stack of contexts if
we allow
any default/scoped annotations.
If annotations are allowed on both types and elements, what I
find even
more difficult are situations where the triple type has one
default, and
the element in "data" with that type has an annotation
specifying the
opposite param value. Do we consider the element to be above the
type in
the scope hierarchy?
For more fun, what if triple is derived some other type where
the
annotation is defined. Would an annotation on the "data" element
be
inherited by the sub-element of type triple, or would the
inheritance
from the triple base type win (i.e. neither the element of the
type
triple or the triple type itself are directly annotated). (Or
consider
an annotation on the "first" element defined in the base type
for triple
rather than on the base type directly - does the element
annotation
inherited from the type hierarchy trump the one from the element
hierarchy?)
An attempt at a picture where only elements have annotations:
Element A : param=littleendian
SubElement B: type ST
Type T:
SubElement C: param:
bigendian
Type ST: subtype of T
What is the param value of element C at A/B/C?
I guess I see a need to keep some hierarchically scoped defaults
(a file
that has some ascii info and then a base64 encoded section of
littleendian stuff), but xsd makes it hard to define a single
hierarchy.
Perhaps some rule of precedence - resolve annotations from type
to
subtype first, then push those onto the stack of element scopes
- would
make things unambiguous, if not user friendly.
Jim
> -----Original Message-----
> From: owner-dfdl-wg at ggf.org [mailto:owner-dfdl-wg at ggf.org] On
> Behalf Of Martin Westhead
> Sent: Friday, November 19, 2004 1:38 PM
> To: Martin Westhead
> Cc: dfdl-wg at gridforum.org
> Subject: Re: [dfdl-wg] Annotation complexity
>
>
> Sorry the elements in the triple were all supposed to be of a
simple
> type e.g.:
>
> <xs:complexType name="triple">
> <xs:annotation>
> <xs:appinfo>
> <dfdlFromBinary/>
> </xs:appinfo>
> </xs:annotation>
> <xs:sequence>
> <xs:element name="first" type="xs:int"/>
> <xs:element name="second" type="xs:int"/>
> <xs:element name="third" type="xs:int"/>
> </xs:sequence>
> </xs:complexType>
>
>
> <xs:complexType name="data">
> <xs:annotation>
> <xs:appinfo>
> <dfdlFromStrings/>
> </xs:appinfo>
> </xs:annotation>
> <xs:sequence>
> <xs:element name="triple"/>
> </xs:sequence>
> </xs:complexType>
>
> Martin Westhead wrote:
> > Hi,
> >
> > I think I understand Suman's issue with annotations on the
Schema
> > tree.
> > (Please Suman tell me if I am right here). The problem is,
that
> > lexically there are many trees in an XSD. Whilst in
> practice these can
> > clearly be considered as a single tree (including, I think,
> even the
> > simple type hierarchies) by placing all the type
> definitions inline,
> > this is not the way they appear to the user. So for example
> if I have a
> > file with conflicting annotations looking like:
> >
> > <xs:complexType name="triple">
> > <xs:annotation>
> > <xs:appinfo>
> > <dfdlFromBinary/>
> > </xs:appinfo>
> > </xs:annotation>
> > <xs:sequence>
> > <xs:element name="first" type="xs:int"/>
> > <xs:element name="second"/>
> > <xs:element name="third"/>
> > </xs:sequence>
> > </xs:complexType>
> >
> >
> > <xs:complexType name="data">
> > <xs:annotation>
> > <xs:appinfo>
> > <dfdlFromStrings/>
> > </xs:appinfo>
> > </xs:annotation>
> > <xs:sequence>
> > <xs:element name="triple"/>
> > </xs:sequence>
> > </xs:complexType>
> >
> > So what I imagined is that we would assume that the "triple"
type is
> > considered _inside_ the scope of the "data" type and so the
> > "dfdlFromBinary" tag wins.
> >
> > On the other hand the user sees two trees of equal depth
with
> > conflicting annotations. The examples can obviously get much
more
> > intricate.
> >
> > The issue is really that the scope of the annotations is
> not lexically
> > defined. At some level this is just like having globally
included
> > variables in a programming language. On the other hand we
> have arbitrary
> > levels of these.
> >
> > Suman is this the problem?
> >
> > If this is the problem, and we agree that it is too
confusing to the
> > user (my opinion is still out on this). Then I see that the
> conclusion
> > is to adopt an approach similar to IBM's that annotations
> can appear
> > only on <element> and <attribute> tags. Even the top level
> of the file
> > is confusing since there may be many files involved. I
> guess we can also
> > have runtime defaults and default settings set in the
> standard. I don't
> > like this conclusion incidentally, can someone convince me
> it is the
> > wrong one?
> >
> > Martin
> >
> >
> >
> >
> >
> >
> >
> >
>
>
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