It seems to me to be important (very desirable) that a large structure with a simple mapping to a representation should be neatly expressible without annotating every leaf element. This really speaks to your last point about defaults. I think tooling defaults are OK, but I also want/need something that I can put in the DFDL file. Suman Kalia wrote:
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@ca.ibm.com ----- Forwarded by Suman Kalia/Toronto/IBM on 11/19/2004 03:04 PM ----- *"Myers, James D" <jim.myers@pnl.gov>* Sent by: owner-dfdl-wg@ggf.org
11/19/2004 02:25 PM
To dfdl-wg@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@ggf.org [mailto:owner-dfdl-wg@ggf.org] On Behalf Of Martin Westhead Sent: Friday, November 19, 2004 1:38 PM To: Martin Westhead Cc: dfdl-wg@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>
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
Martin Westhead wrote: 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